title: Copper conductor

text: Twisted pair cabling is the most popular network cable and is often used in data networks for short and medium length connections (up to 100 meters or 328 feet). This is due to its relatively lower costs compared to optical fiber and coaxial cable.


title: Copper conductor

text: Unshielded twisted pair (UTP) cables are the primary cable type for telephone usage. In the late 20th century, UTPs emerged as the most common cable in computer networking cables, especially as patch cables or temporary network connections. They are increasingly used in video applications, primarily in security cameras.


title: Copper conductor

text: UTP plenum cables that run above ceilings and inside walls use a solid copper core for each conductor, which enables the cable to hold its shape when bent. Patch cables, which connect computers to wall plates, use stranded copper wire because they are expected to be flexed during their lifetimes.


title: Copper conductor

text: UTPs are the best balanced line wires available. However they are the easiest to tap into. When interference and security are concerns, shielded cable or fiber optic cable is often considered.


title: Copper conductor

text: UTP cables include: Category 3 cable, now the minimum requirement by the FCC (USA) for every telephone connection; Category 5e cable, 100-MHz enhanced pairs for running Gigabit Ethernet (1000Base-T); and Category 6 cable, where each pair runs 250 MHz for improved 1000Base-T performance.


title: Copper conductor

text: In copper twisted pair wire networks, copper cable certification is achieved through a thorough series of tests in accordance with Telecommunications Industry Association (TIA) or International Organization for Standardization (ISO) standards.


title: Copper conductor

text: Coaxial cables were extensively used in mainframe computer systems and were the first type of major cable used for Local Area Networks (LAN). Common applications for coaxial cable today include computer network (Internet) and instrumentation data connections, video and CATV distribution, RF and microwave transmission, and feedlines connecting radio transmitters and receivers with their antennas.


title: Copper conductor

text: While coaxial cables can go longer distances and have better protection from EMI than twisted pairs, coaxial cables are harder to work with and more difficult to run from offices to the wiring closet. For these reasons, it is now generally being replaced with less expensive UTP cables or by fiber optic cables for more capacity.


title: Copper conductor

text: Today, many CATV companies still use coaxial cables into homes. These cables, however, are increasingly connected to a fiber optic data communications system outside of the home. Most building management systems use proprietary copper cabling, as do paging/audio speaker systems. Security monitoring and entry systems still often depend on copper, although fiber cables are also used.


title: Copper conductor

text: Most telephone lines can share voice and data simultaneously. Pre-digital quad telephone wiring in homes is unable to handle communications needs for multiple phone lines, Internet service, video communications, data transmission, fax machines, and security services. Crosstalk, static interference, inaudible signals, and interrupted service are common problems with outdated wiring. Computers connected to old-fashioned communications wiring often experience poor Internet performance.


title: Copper conductor

text: “Structured wiring” is the general term for 21st century On-premises wiring for high-capacity telephone, video, data-transmission, security, control, and entertainment systems. Installations usually include a central distribution panel where all connections are made, as well as outlets with dedicated connections for phone, data, TV and audio jacks.


title: Copper conductor

text: Structured wiring enables computers to communicate with each other error-free and at high speeds while resisting interference among various electrical sources, such as household appliances and external communications signals. Networked computers are able to share high-speed Internet connections simultaneously. Structured wiring can also connect computers with printers, scanners, telephones, fax machines, and even home security systems and home entertainment equipment.


title: Copper conductor

text: A star wiring pattern, where the wiring to each jack extends to a central distribution device, facilitates flexibility of services, problem identification, and better signal quality. This pattern has advantages to daisy chain loops. Installation tools, tips, and techniques for networked wiring systems using twisted pairs, coaxial cables, and connectors for each are available.


title: Copper conductor

text: Structured wiring competes with wireless systems in homes. While wireless systems certainly have convenience advantages, they also have drawbacks over copper-wired systems: the higher bandwidth of systems using Category 5e wiring typically support more than ten times the speeds of wireless systems for faster data applications and more channels for video applications. Alternatively, wireless systems are a security risk as they can transmit sensitive information to unintended users over similar receiver devices. Wireless systems are more susceptible to interference from other devices and systems, which can compromise performance. Certain geographic areas and some buildings may be unsuitable for wireless installations, just as some buildings may present difficulties installing wires.


title: Copper conductor

text: Power distribution is the final stage in the delivery of electricity for an end use. A power distribution system carries electricity from the transmission system to consumers.


title: Copper conductor

text: Power cables are used for the transmission and distribution of electric power, either outdoors or inside buildings. Details on the various types of power cables are available.


title: Copper conductor

text: Copper is the preferred conductor material for underground transmission lines operating at high and extra-high voltages to 400 kV. The predominance of copper underground systems stems from its higher volumetric electrical and thermal conductivities compared to other conductors. These beneficial properties for copper conductors conserve space, minimize power loss, and maintain lower cable temperatures.


title: Copper conductor

text: Copper continues to dominate low-voltage lines in mines and underwater applications, as well as in electric railroads, hoists, and other outdoor services.


title: Copper conductor

text: Aluminium, either alone or reinforced with steel, is the preferred conductor for overhead transmission lines due to its lighter weight and lower cost.


title: Copper conductor

text: Appliance conductors for domestic applications and instruments are manufactured from bunch-stranded soft wire, which may be tinned for soldering or phase identification. Depending upon loads, insulation can be PVC, neoprene, ethylene propylene, polypropylene filler, or cotton.


title: Copper conductor

text: Automotive conductors require insulation that is resistant to elevated temperatures, petroleum products, humidity, fire, and chemicals. PVC, neoprene, and polyethylene are the most common insulators. Potentials range from 12 V for electrical systems to between 300 V - 15,000 V for instruments, lighting, and ignition systems.


title: Copper conductor

text: Magnet wire or winding wire is used in windings of electric motors, transformers, inductors, generators, headphones, loudspeaker coils, hard drive head positioners, electromagnets, and other devices.


title: Copper conductor

text: Most often, magnetic wire is composed of fully annealed, electrolytically refined copper to allow closer winding when making electromagnetic coils. The wire is coated with a range of polymeric insulations, including varnish, rather than the thicker plastic or other types of insulation commonly used on electrical wire. High-purity oxygen-free copper grades are used for high-temperature applications in reducing atmospheres or in motors or generators cooled by hydrogen gas.


title: Copper conductor

text: A copper splice closure is defined as an enclosure, and the associated hardware, that is intended to restore the mechanical and environmental integrity of one or more


title: Copper conductor

text: copper cables entering the enclosure and providing some internal function for splicing, termination, or interconnection.


title: Copper conductor

text: As stated in Telcordia industry requirements document GR-3151, there are two principal configurations for closures: butt closures and in-line closures. Butt closures permit cables to enter the closure from one end only. This design may also be referred to as a dome closure. These closures can be used in a variety of applications, including branch splicing. In-line closures provide for the entry of cables at both ends of the closure. They can be used in a variety of applications, including branch splicing and cable access. In-line closures can also be used in a butt configuration by restricting cable access to one end of the closure.


title: Copper conductor

text: A copper splice closure is defined by the functional design characteristics and, for the most part, is independent of specific deployment environments or applications. At this time, Telcordia has identified two types of copper closures:


title: Copper conductor

text: ESCs provide all of the features and functions expected of a typical splice closure in an enclosure that prevents the intrusion of liquid and vapor into the closure interior. This is accomplished through the use of an environmental sealing system such as rubber gaskets or hot-melt adhesives. Some ESCs use pressurized air to help keep moisture out of the closure.


title: Copper conductor

text: FBCs provide all of the features and functions expected of a typical splice closure that prevents the intrusion of wind-driven rain, dust, and insects. Such a closure, however, permits the free exchange of air with the outside environment. Therefore, it is possible that condensation will form inside the closure. It is thus necessary to provide adequate drainage to prevent the accumulation of water inside the closure.


title: Copper conductor

text: Copper will continue to be the predominant material in most electrical wire applications, especially where space considerations are important. The automotive industry for decades has considered the use of smaller-diameter wires in certain applications. Many manufacturers are beginning to use copper alloys such as copper-magnesium (CuMg), which allow for smaller diameter wires with less weight and improved conductivity performance. Special alloys like copper-magnesium are beginning to see increased usage in automotive, aerospace, and defense applications.


title: Copper conductor

text: Due to the need to increase the transmission of high-speed voice and data signals, the surface quality of copper wire is expected to continue to improve. Demands for better drawability and movement towards “zero” defects in copper conductors are expected to continue.


title: Copper conductor

text: A minimum mechanical strength requirement for magnet wire may evolve in order to improve formability and prevent excessive stretching of wire during high speed coiling operations.


title: Copper conductor

text: It does not seem likely that standards for copper wire purity will increase beyond the current minimum value of 101% IACS. Although 6-nines copper (99.9999% pure) has been produced in small quantities, it is extremely expensive and probably unnecessary for most commercial applications such as magnet, telecommunications, and building wire. The electrical conductivity of 6-nines copper and 4-nines copper (99.99% pure) is nearly the same at ambient temperature, although the higher-purity copper has a higher conductivity at cryogenic temperatures. Therefore, for non-cryogenic temperatures, 4-nines copper will probably remain the dominant material for most commercial wire applications.


title: Copper conductor

text: During the 2000s commodities boom, copper prices increased worldwide, increasing the incentive for criminals to steal copper from power supply and communications cables.


title: Brushed DC electric motor

text: A brushed DC electric motor is an internally commutated electric motor designed to be run from a direct current power source and utilizing an electric brush for contact.


title: Brushed DC electric motor

text: Brushed motors were the first commercially important application of electric power to driving mechanical energy, and DC distribution systems were used for more than 100 years to operate motors in commercial and industrial buildings. Brushed DC motors can be varied in speed by changing the operating voltage or the strength of the magnetic field. Depending on the connections of the field to the power supply, the speed and torque characteristics of a brushed motor can be altered to provide steady speed or speed inversely proportional to the mechanical load. Brushed motors continue to be used for electrical propulsion, cranes, paper machines and steel rolling mills. Since the brushes wear down and require replacement, brushless DC motors using power electronic devices have displaced brushed motors from many applications.


title: Brushed DC electric motor

text: When a current passes through the coil wound around a soft iron core situated inside an external magnetic field, the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. According to Fleming's left hand rule, the forces cause a turning effect on the coil, making it rotate. To make the motor rotate in a constant direction, "direct current" commutators make the current reverse in direction every half a cycle (in a two-pole motor) thus causing the motor to continue to rotate in the same direction.


title: Brushed DC electric motor

text: A problem with the motor shown above is that when the plane of the coil is parallel to the magnetic field—i.e. when the rotor poles are 90 degrees from the stator poles—the torque is zero. In the pictures above, this occurs when the core of the coil is horizontal—the position it is just about to reach in the second-to-last picture on the right. The motor would not be able to start in this position. However, once it was started, it would continue to rotate through this position by momentum.


title: Brushed DC electric motor

text: There is a second problem with this simple pole design. At the zero-torque position, both commutator brushes are touching (bridging) both commutator plates, resulting in a short circuit. The power leads are shorted together through the commutator plates, and the coil is also short-circuited through both brushes (the coil is shorted twice, once through each brush independently). Note that this problem is independent of the non-starting problem above; even if there were a high current in the coil at this position, there would still be zero torque. The problem here is that this short uselessly consumes power without producing any motion (nor even any coil current.) In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful. However, if a two-pole motor were designed to do actual work with several hundred watts of power output, this shorting could result in severe commutator overheating, brush damage, and potential welding of the brushes—if they were metallic—to the commutator. Carbon brushes, which are often used, would not weld. In any case, a short like this is very wasteful, drains batteries rapidly and, at a minimum, requires power supply components to be designed to much higher standards than would be needed just to run the motor without the shorting.


title: Brushed DC electric motor

text: One simple solution is to put a gap between the commutator plates which is wider than the ends of the brushes. This increases the zero-torque range of angular positions but eliminates the shorting problem; if the motor is started spinning by an outside force it will continue spinning. With this modification, it can also be effectively turned off simply by stalling (stopping) it in a position in the zero-torque (i.e. commutator non-contacting) angle range. This design is sometimes seen in homebuilt hobby motors, e.g. for science fairs and such designs can be found in some published science project books. A clear downside of this simple solution is that the motor now coasts through a substantial arc of rotation twice per revolution and the torque is pulsed. This may work for electric fans or to keep a flywheel spinning but there are many applications, even where starting and stopping are not necessary, for which it is completely inadequate, such as driving the capstan of a tape transport, or any similar instance where to speed up and slow down often and quickly is a requirement. Another disadvantage is that, since the coils have a measure of self inductance, current flowing in them cannot suddenly stop. The current attempts to jump the opening gap between the commutator segment and the brush, causing arcing.


title: Brushed DC electric motor

text: Even for fans and flywheels, the clear weaknesses remaining in this design—especially that it is not self-starting from all positions—make it impractical for working use, especially considering the better alternatives that exist. Unlike the demonstration motor above, DC motors are commonly designed with more than two poles, are able to start from any position, and do not have any position where current can flow without producing electromotive power by passing through some coil. Many common small brushed DC motors used in toys and small consumer appliances, the simplest mass-produced DC motors to be found, have three-pole armatures. The brushes can now bridge two adjacent commutator segments without causing a short circuit. These three-pole armatures also have the advantage that current from the brushes either flows through two coils in series or through just one coil. Starting with the current in an individual coil at half its nominal value (as a result of flowing through two coils in series), it rises to its nominal value and then falls to half this value. The sequence then continues with current in the reverse direction. This results in a closer step-wise approximation to the ideal sinusoidal coil current, producing a more even torque than the two-pole motor where the current in each coil is closer to a square wave. Since current changes are half those of a comparable two-pole motor, arcing at the brushes is consequently less.


title: Brushed DC electric motor

text: If the shaft of a DC motor is turned by an external force, the motor will act like a generator and produce an Electromotive force (EMF). During normal operation, the spinning of the motor produces a voltage, known as the counter-EMF (CEMF) or back EMF, because it opposes the applied voltage on the motor. The back EMF is the reason that the motor when free-running does not appear to have the same low electrical resistance as the wire contained in its winding. This is the same EMF that is produced when the motor is used as a generator (for example when an electrical load, such as a light bulb, is placed across the terminals of the motor and the motor shaft is driven with an external torque). Therefore, the total voltage drop across a motor consists of the CEMF voltage drop, and the parasitic voltage drop resulting from the internal resistance of the armature's windings. The current through a motor is given by the following equation:


title: Brushed DC electric motor

text: As an unloaded DC motor spins, it generates a backwards-flowing electromotive force that resists the current being applied to the motor. The current through the motor drops as the rotational speed increases, and a free-spinning motor has very little current. It is only when a load is applied to the motor that slows the rotor that the current draw through the motor increases.


title: Brushed DC electric motor

text: In a dynamo, a plane through the centers of the contact areas where a pair of brushes touch the commutator and parallel to the axis of rotation of the armature is referred to as the "commutating plane". In this diagram the commutating plane is shown for just one of the brushes, assuming the other brush made contact on the other side of the commutator with radial symmetry, 180 degrees from the brush shown.


title: Brushed DC electric motor

text: In a real dynamo, the field is never perfectly uniform. Instead, as the rotor spins it induces field effects which drag and distort the magnetic lines of the outer non-rotating stator.


title: Brushed DC electric motor

text: The faster the rotor spins, the further the degree of field distortion. Because the dynamo operates most efficiently with the rotor field at right angles to the stator field, it is necessary to either retard or advance the brush position to put the rotor's field into the correct position to be at a right angle to the distorted field.


title: Brushed DC electric motor

text: These field effects are reversed when the direction of spin is reversed. It is therefore difficult to build an efficient reversible commutated dynamo, since for highest field strength it is necessary to move the brushes to the opposite side of the normal neutral plane.


title: Brushed DC electric motor

text: The effect can be considered to be somewhat similar to timing advance in an internal combustion engine. Generally a dynamo that has been designed to run at a certain fixed speed will have its brushes permanently fixed to align the field for highest efficiency at that speed.


title: Brushed DC electric motor

text: DC machines with wound stators compensate the distortion with commutating field windings and compensation windings.


title: Brushed DC electric motor

text: The field coils have traditionally existed in four basic formats: separately excited (sepex), series-wound, shunt-wound, and a combination of the latter two; compound-wound.


title: Brushed DC electric motor

text: In a series wound motor, the field coils are connected electrically in series with the armature coils (via the brushes). In a shunt wound motor, the field coils are connected in parallel, or "shunted" to the armature coils. In a separately excited (sepex) motor the field coils are supplied from an independent source, such as a motor-generator and the field current is unaffected by changes in the armature current. The sepex system was sometimes used in DC traction motors to facilitate control of wheelslip.


title: Brushed DC electric motor

text: Permanent-magnet types have some performance advantages over direct-current, excited, synchronous types, and have become predominant in fractional horsepower applications. They are smaller, lighter, more efficient and reliable than other singly-fed electric machines.


title: Brushed DC electric motor

text: Originally all large industrial DC motors used wound field or rotor magnets. Permanent magnets have traditionally only been useful on small motors because it was difficult to find a material capable of retaining a high-strength field. Only recently have advances in materials technology allowed the creation of high-intensity permanent magnets, such as neodymium magnets, allowing the development of compact, high-power motors without the extra volume of field coils and excitation means. But as these high performance permanent magnets become more applied in electric motor or generator systems, other problems are realized (see Permanent magnet synchronous generator).


title: Brushed DC electric motor

text: Traditionally, the field has been applied radially—in and away from the rotation axis of the motor. However some designs have the field flowing along the axis of the motor, with the rotor cutting the field lines as it rotates. This allows for much stronger magnetic fields, particularly if halbach arrays are employed. This, in turn, gives power to the motor at lower speeds. However, the focused flux density cannot rise about the limited residual flux density of the permanent magnet despite high coercivity and like all electric machines, the flux density of magnetic core saturation is the design constraint.


title: Brushed DC electric motor

text: Generally, the rotational speed of a DC motor is proportional to the EMF in its coil (= the voltage applied to it minus voltage lost on its resistance), and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. A simulation example can be found here and. The direction of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors). The effective voltage can be varied by inserting a series resistor or by an electronically controlled switching device made of thyristors, transistors, or, formerly, mercury arc rectifiers.


title: Brushed DC electric motor

text: Series-parallel control was the standard method of controlling railway traction motors before the advent of power electronics. An electric locomotive or train would typically have four motors which could be grouped in three different ways:


title: Brushed DC electric motor

text: This provided three running speeds with minimal resistance losses. For starting and acceleration, additional control was provided by resistances. This system has been superseded by electronic control systems.


title: Brushed DC electric motor

text: The speed of a DC motor can be increased by field weakening. Reducing the field strength is done by inserting resistance in series with a shunt field, or inserting resistances around a series-connected field winding, to reduce current in the field winding. When the field is weakened, the back-emf reduces, so a larger current flows through the armature winding and this increases the speed. Field weakening is not used on its own but in combination with other methods, such as series-parallel control.


title: Brushed DC electric motor

text: In a circuit known as a chopper, the average voltage applied to the motor is varied by switching the supply voltage very rapidly. As the "on" to "off" ratio is varied to alter the average applied voltage, the speed of the motor varies. The percentage "on" time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% "on" time, the average voltage at the motor will be 25 V. During the "off" time, the armature's inductance causes the current to continue through a diode called a "flyback diode", in parallel with the motor. At this point in the cycle, the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage "on" time is 100%. At 100% "on" time, the supply and motor current are equal. The rapid switching wastes less energy than series resistors. This method is also called pulse-width modulation (PWM) and is often controlled by a microprocessor. An output filter is sometimes installed to smooth the average voltage applied to the motor and reduce motor noise.


title: Brushed DC electric motor

text: Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives, and trams. Another application is starter motors for petrol and small diesel engines. Series motors must never be used in applications where the drive can fail (such as belt drives). As the motor accelerates, the armature (and hence field) current reduces. The reduction in field causes the motor to speed up, and in extreme cases the motor can even destroy itself, although this is much less of a problem in fan-cooled motors (with self-driven fans). This can be a problem with railway motors in the event of a loss of adhesion since, unless quickly brought under control, the motors can reach speeds far higher than they would do under normal circumstances. This can not only cause problems for the motors themselves and the gears, but due to the differential speed between the rails and the wheels it can also cause serious damage to the rails and wheel treads as they heat and cool rapidly. Field weakening is used in some electronic controls to increase the top speed of an electric vehicle. The simplest form uses a contactor and field-weakening resistor; the electronic control monitors the motor current and switches the field weakening resistor into circuit when the motor current reduces below a preset value (this will be when the motor is at its full design speed). Once the resistor is in circuit, the motor will increase speed above its normal speed at its rated voltage. When motor current increases, the control will disconnect the resistor and low speed torque is made available.


title: Brushed DC electric motor

text: A Ward Leonard control is usually used for controlling a shunt or compound wound DC motor, and developed as a method of providing a speed-controlled motor from an AC supply, though it is not without its advantages in DC schemes. The AC supply is used to drive an AC motor, usually an induction motor that drives a DC generator or dynamo. The DC output from the armature is directly connected to the armature of the DC motor (sometimes but not always of identical construction). The shunt field windings of both DC machines are independently excited through variable resistors. Extremely good speed control from standstill to full speed, and consistent torque, can be obtained by varying the generator and/or motor field current. This method of control was the "de facto" method from its development until it was superseded by solid state thyristor systems. It found service in almost any environment where good speed control was required, from passenger lifts through to large mine pit head winding gear and even industrial process machinery and electric cranes. Its principal disadvantage was that three machines were required to implement a scheme (five in very large installations, as the DC machines were often duplicated and controlled by a tandem variable resistor). In many applications, the motor-generator set was often left permanently running, to avoid the delays that would otherwise be caused by starting it up as required. Although electronic (thyristor) controllers have replaced most small to medium Ward-Leonard systems, some very large ones (thousands of horsepower) remain in service. The field currents are much lower than the armature currents, allowing a moderate sized thyristor unit to control a much larger motor than it could control directly. For example, in one installation, a 300 amp thyristor unit controls the field of the generator. The generator output current is in excess of 15,000 amperes, which would be prohibitively expensive (and inefficient) to control directly with thyristors.


title: Brushed DC electric motor

text: A DC motor's speed and torque characteristics vary according to three different magnetization sources, separately excited field, self-excited field or permanent-field, which are used selectively to control the motor over the mechanical load's range. Self-excited field motors can be series, shunt, or a compound wound connected to the armature.


title: Brushed DC electric motor

text: The DC motor's counter emf is proportional to the product of the machine's total flux strength and armature speed:


title: Brushed DC electric motor

text: The DC motor's input voltage must overcome the counter emf as well as the voltage drop created by the armature current across the motor resistance, that is, the combined resistance across the brushes, armature winding and series field winding, if any:


title: Brushed DC electric motor

text: The DC motor's torque is proportional to the product of the armature current and the machine's total flux strength:


title: Brushed DC electric motor

text: With the shunt wound motor's high-resistance field winding connected in parallel with the armature, V, R and Ø are constant such that the no load to full load speed regulation is seldom more than 5%. Speed control is achieved three ways:


title: Brushed DC electric motor

text: The series motor responds to increased load by slowing down; the current increases and the torque rises in proportional to the square of the current since the same current flows in both the armature and the field windings. If the motor is stalled, the current is limited only by the total resistance of the windings and the torque can be very high, but there is a danger of the windings becoming overheated. Series wound motors were widely used as traction motors in rail transport of every kind, but are being phased out in favour of power inverter-fed AC induction motors. The counter EMF aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate, the counter EMF is zero and the only factor limiting the armature current is the armature resistance. As the prospective current through the armature is very large, the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter EMF. As the motor rotation builds up, the resistance is gradually cut out.


title: Brushed DC electric motor

text: The series wound DC motor's most notable characteristic is that its speed is almost entirely dependent on the torque required to drive the load. This suits large inertial loads as motor accelerates from maximum torque, torque reducing gradually as speed increases.


title: Brushed DC electric motor

text: As the series motor's speed can be dangerously high, series motors are often geared or direct-connected to the load.


title: Brushed DC electric motor

text: A permanent magnet DC motor is characterized by a linear relationship between stall torque when the torque is maximum with the shaft at standstill and no-load speed with no applied shaft torque and maximum output speed. There is a quadratic power relationship between these two speed-axis points.


title: Brushed DC electric motor

text: To extend a DC motor's service life, protective devices and motor controllers are used to protect it from mechanical damage, excessive moisture, high dielectric stress and high temperature or thermal overloading. These protective devices sense motor fault conditions and either activate an alarm to notify the operator or automatically de-energize the motor when a faulty condition occurs. For overloaded conditions, motors are protected with thermal overload relays. Bi-metal thermal overload protectors are embedded in the motor's windings and made from two dissimilar metals. They are designed such that the bimetallic strips will bend in opposite directions when a temperature set point is reached to open the control circuit and de-energize the motor. Heaters are external thermal overload protectors connected in series with the motor's windings and mounted in the motor contactor. Solder pot heaters melt in an overload condition, which cause the motor control circuit to de-energize the motor. Bimetallic heaters function the same way as embedded bimetallic protectors. Fuses and circuit breakers are overcurrent or short circuit protectors. Ground fault relays also provide overcurrent protection. They monitor the electric current between the motor's windings and earth system ground. In motor-generators, reverse current relays prevent the battery from discharging and motorizing the generator. Since D.C. motor field loss can cause a hazardous runaway or overspeed condition, loss of field relays are connected in parallel with the motor's field to sense field current. When the field current decreases below a set point, the relay will deenergize the motor's armature. A locked rotor condition prevents a motor from accelerating after its starting sequence has been initiated. Distance relays protect motors from locked-rotor faults. Undervoltage motor protection is typically incorporated into motor controllers or starters. In addition, motors can be protected from overvoltages or surges with isolation transformers, power conditioning equipment, MOVs, arresters and harmonic filters. Environmental conditions, such as dust, explosive vapors, water, and high ambient temperatures, can adversely affect the operation of a DC motor. To protect a motor from these environmental conditions, the National Electrical Manufacturers Association (NEMA) and the International Electrotechnical Commission (IEC) have standardized motor enclosure designs based upon the environmental protection they provide from contaminants. Modern software can also be used in the design stage, such as Motor-CAD, to help increase the thermal efficiency of a motor.


title: Brushed DC electric motor

text: The counter-emf aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant the counter-emf is zero and the only factor limiting the armature current is the armature resistance and inductance. Usually the armature resistance of a motor is less than 1 Ω; therefore the current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices.


title: Brushed DC electric motor

text: Therefore, the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-emf. As the motor rotation builds up, the resistance is gradually cut out.


title: Brushed DC electric motor

text: When electrical and DC motor technology was first developed, much of the equipment was constantly tended by an operator trained in the management of motor systems. The very first motor management systems were almost completely manual, with an attendant starting and stopping the motors, cleaning the equipment, repairing any mechanical failures, and so forth.


title: Brushed DC electric motor

text: The first DC motor-starters were also completely manual, as shown in this image. Normally it took the operator about ten seconds to slowly advance the rheostat across the contacts to gradually increase input power up to operating speed. There were two different classes of these rheostats, one used for starting only, and one for starting and speed regulation. The starting rheostat was less expensive, but had smaller resistance elements that would burn out if required to run a motor at a constant reduced speed.


title: Brushed DC electric motor

text: This starter includes a no-voltage magnetic holding feature, which causes the rheostat to spring to the off position if power is lost, so that the motor does not later attempt to restart in the full-voltage position. It also has overcurrent protection that trips the lever to the off position if excessive current over a set amount is detected.


title: Brushed DC electric motor

text: The incoming power wires are called L1 and L2. As the name implies there are only three connections to the starter, one to incoming power, one to the armature, and one to the field. The connections to the armature are called A1 and A2. The ends of the field (excitement) coil are called F1 and F2. In order to control the speed, a field rheostat is connected in series with the shunt field. One side of the line is connected to the arm of the starter. The arm is spring-loaded so, it will return to the "Off" position when not held at any other position.


title: Brushed DC electric motor

text: The four-point starter eliminates the drawback of the three-point starter. In addition to the same three points that were in use with the three-point starter, the other side of the line, L1, is the fourth point brought to the starter when the arm is moved from the "Off" position. The coil of the holding magnet is connected across the line. The holding magnet and starting resistors function identical as in the three-point starter.


title: Solar thermal collector

text: A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and solar towers or non water heating devices such as solar air heaters.


title: Solar thermal collector

text: Solar thermal collectors are either non-concentrating or concentrating. In non-concentrating collectors, the aperture area (i.e., the area that receives the solar radiation) is roughly the same as the absorber area (i.e., the area absorbing the radiation). A common example of such a system is a metal plate that is painted a dark color to maximize the absorption of sunlight. The energy is then collected by cooling the plate with a working fluid, often water or glycol running in pipes attached to the plate.


title: Solar thermal collector

text: Concentrating collectors have a much larger aperture than the absorber area. The aperture is typically in the form of a mirror that is focussed on the absorber, which in most cases are the pipes carrying the working fluid. Due to the movement of the sun during the day, concentrating collectors often require some form of solar tracking system, and are sometimes referred to "active" collectors for this reason.


title: Solar thermal collector

text: Non-concentrating collectors are typically used in residential, industrial and commercial buildings for space heating, while concentrating collectors in concentrated solar power plants generate electricity by heating a heat-transfer fluid to drive a turbine connected to an electrical generator.


title: Solar thermal collector

text: Flat-plate and evacuated-tube solar collectors are mainly used to collect heat for space heating, domestic hot water, or cooling with an absorption chiller. In contrast to solar hot water panels, they use a circulating fluid to displace heat to a separated reservoir. The first solar thermal collector designed for building roofs was patented by William H. Goettl and called the "Solar heat collector and radiator for building roof".


title: Solar thermal collector

text: Evacuated flat-plate solar collectors are a more recent innovation and can be used for Solar Heat for Industrial Cooling (SHIC) and Solar Air Conditioning (SAC), where temperature in excess of are required. These non-concentrating collectors harvest both diffuse and direct light and can make use of steam instead of water as fluid.


title: Solar thermal collector

text: Flat-plate collectors are the most common solar thermal technology in Europe. They consist of an (1) enclosure containing (2) a dark-colored absorber plate with fluid circulation passageways, and (3) a transparent cover to allow transmission of solar energy into the enclosure. The sides and back of the enclosure are typically insulated to reduce heat loss to the ambient. A heat transfer fluid is circulated through the absorber's fluid passageways to remove heat from the solar collector. The circulation fluid in tropical and sub-tropical climates is typically water. In climates where freezing is likely, a heat transfer fluid similar to an automotive antifreeze solution may be used instead of water, or in a mixture with water. If a heat transfer fluid is used, a heat exchanger is typically employed to transfer heat from the solar collector fluid to a hot water storage tank. The most common absorber design consists of copper tubing joined to a high conductivity metal sheet (copper or aluminum). A dark coating is applied to the sun-facing side of the absorber assembly to increase its absorption of solar energy. A common absorber coating is black enamel paint.


title: Solar thermal collector

text: In higher performance solar collector designs, the transparent cover is tempered soda-lime glass having reduced iron oxide content same as for photovoltaic solar panels. The glass may also have a stippling pattern and one or two anti-reflective coatings to further enhance transparency. The absorber coating is typically a selective coating, where selective stands for having the special optical property to combine high absorption in the visible part of the electromagnetic spectrum coupled to low emittance in the infrared one. This creates a selective surface, which reduces black body energy emission from the absorber and improves performance. Piping can be laser or ultrasound welded to the absorber sheet to reduce damage to the selective coating, which is typically applied prior to joining to large coils in a roll-to-roll process.


title: Solar thermal collector

text: A flat plate collector making use of a honeycomb structure to reduce heat loss also at the glass side too has also been made available commercially. Most flat plate collectors have a life expectancy of over 25 years..


title: Solar thermal collector

text: Evacuated tube collectors are the most common solar thermal technology in the world. They make use of a glass tube to surround the absorber with high vacuum and effectively resist atmospheric pressure. The vacuum that surrounds the absorber greatly reduces convection and conduction heat loss, therefore achieving greater energy conversion efficiency. The absorber can be either metallic as in the case of flat plate collectors or being a second concentric glass tube ("Sydney Tube"). Heat transfer fluid can flow in and out of each tube or being in contact with a heat pipe reaching inside the tube. For the latter, heat pipes transfer heat to the fluid in a heat exchanger called a "manifold" placed transversely with respect to the tubes. The manifold is wrapped in insulation (glass wool) and covered by a protective metal or plastic case also used for fixing to supports.


title: Solar thermal collector

text: Glass-metal evacuated tubes are made with flat or curved metal absorber sheets same as those of flat plates. These sheets are joined to pipes or heat pipes to make "fins" and placed inside a single borosilicate glass tube. An anti-reflective coating can be deposited on the inner and outer surfaces of such tubes to improve transparency. Both selective and anti-reflective coating (inner tube surface) will not degrade until the vacuum is lost. A high vacuum-tight glass-metal seal is however required at one or both sides of each evacuated tube. This seal is cycled between ambient and fluid temperature each day of collector operation and might lead to failures in time.


title: Solar thermal collector

text: Glass-glass evacuated tubes are made with two borosilicate glass tubes fused together at one or both ends (similar a vacuum bottle or dewar flask). The absorber fin is placed inside the inner tube at atmospheric pressure. Glass-glass tubes have a very reliable seal, but the two layers of glass reduce the amount of sunlight that reaches the absorber. The selective coating can be deposited on the inner borosilicate tube (high vacuum side) to avoid this, but heat has then to flow through the poorly conducting glass thickness of the inner tube in this case. Moreover, moisture may enter the non-evacuated area inside the inner tube and cause absorber corrosion in particular when made from dissimilar materials (galvanic corrosion).


title: Solar thermal collector

text: A Barium flash getter pump is commonly evaporated inside the high vacuum gap in between tubes to keep the internal pressure stable through time.


title: Solar thermal collector

text: The high temperatures that can occur inside evacuated tubes may require special design to prevent overheating. Some evacuated tube collectors work as a thermal one-way valve due to their heat pipes. This gives them an inherent maximum operating temperature that acts as a safety feature. Evacuated tubes collectors can also be provided with low concentrating reflectors at the back of the tubes realising a CPC collector.


title: Solar thermal collector

text: A longstanding argument exists between proponents of these two technologies. Some of this can be related to the structure of evacuated tube collectors which have a discontinuous absorbance area. An array of evacuated tubes collectors on a roof has space between the individual tubes and a vacuum gap between each tube and its absorber inside, covering only a fraction of the installation area on a roof. If evacuated tubes are compared with flat-plate collectors on the basis of the area of roof occupied (gross area), a different conclusion might be reached than if the absorber or aperture areas were compared. The recent revision of the ISO 9806 standard states that the efficiency of solar thermal collectors should be measured in terms of gross area and this might favour flat plates in respect to evacuated tube collectors in direct comparisons.


title: Solar thermal collector

text: Flat-plate collectors usually lose more heat to the environment than evacuated tubes because there is no insulation at the glass side. Evacuated tube collectors intrinsically have a lower absorber to gross area ratio (typically 60–80% less) than flat plates because tubes have to be spaced apart. Although several European companies manufacture evacuated tube collectors (mainly glass-metal type), the evacuated tube market is dominated by manufacturers in China, with some companies having track records of 15–30 years or more. There is no unambiguous evidence that the two designs differ in long-term reliability. However, evacuated tube technology (especially for newer variants with glass-metal seals and heat pipes) still needs to demonstrate competitive lifetimes. The modularity of evacuated tubes can be advantageous in terms of extensibility and maintenance, for example, if the vacuum in one heat pipe tube is lost it can be easily be replaced with minimal effort.


title: Solar thermal collector

text: In most climates, flat plate collectors will generally be more cost-effective than evacuated tubes. However, evacuated tube collectors are well-suited to cold ambient temperatures and work well in situations of low solar irradiance, providing heat more consistently throughout the year. Unglazed flat plate collectors are the preferred devices for heating swimming pool water. Unglazed collectors may be suitable in tropical or subtropical environments if domestic hot water needs to be heated by less than over ambient temperature. Evacuated tube collectors have less aerodynamic drag, which may allow for a simpler installation on roofs in windy locations. The gaps between the tubes may allow for snow to fall through the collector, minimizing the loss of production in some snowy conditions, though the lack of radiated heat from the tubes can also prevent effective shedding of accumulated snow. Flat plate collectors might be easier to clean. Other properties, such as appearance and ease of installation are more subjective and difficult to compare.


title: Solar thermal collector

text: Evacuated flat plate solar collectors provide all the advantages of both flat plate and evacuated tube collectors combined together. They surround a large area metal sheet absorber with high vacuum inside a flat envelope made of glass and metal. They offer the highest energy conversion efficiency of any non-concentrating solar thermal collector, but require sophisticated technology for manufacturing. They should not be confused with flat plate collectors featuring low vacuum inside. The first collector making use of high vacuum insulation was developed at CERN, while TVP SOLAR SA of Switzerland was the first company to commercialise Solar Keymark certified collectors in 2012.


title: Solar thermal collector

text: Evacuated flat plate solar collectors require both a glass-metal seal to join the glass plate to the rest of the metal envelope and an internal structure to support such plate against atmospheric pressure. The absorber has to be segmented or provided with suitable holes to accommodate such structure. Joining of all parts has to be high vacuum-tight and only materials with low vapour pressure can be used to prevent outgassing. Glass-metal seal technology can be based either on metallized glass or vitrified metal and defines the type of collector. Different from evacuated tube collectors, they make use of non-evaporable getter (NEG) pumps to keep the internal pressure stable through time. This getter pump technology has the advantage of providing some regeneration in-situ by exposure to sunlight. Evacuated flat plate solar collectors have been studied for solar air condition and compared to compact solar concentrators.


title: Solar thermal collector

text: These collectors are an alternative to metal collectors and are now being produced in Europe. These may be wholly polymer, or they may include metal plates in front of freeze-tolerant water channels made of silicone rubber. Polymers are flexible and therefore freeze-tolerant and can employ plain water instead of antifreeze, so that they may be plumbed directly into existing water tanks instead of needing heat exchangers that lower efficiency. By dispensing with a heat exchanger, temperatures need not be quite so high for the circulation system to be switched on, so such direct circulation panels, whether polymer or otherwise, can be more efficient, particularly at low solar irradiance levels. Some early selectively coated polymer collectors suffered from overheating when insulated, as stagnation temperatures can exceed the polymer's melting point. For example, the melting point of polypropylene is , while the stagnation temperature of insulated thermal collectors can exceed if control strategies are not used. For this reason, polypropylene is not often used in glazed selectively coated solar collectors. Increasingly, polymers such as high temperate silicones (which melt at over ) are being used. Some non polypropylene polymer based glazed solar collectors are matte black coated rather than selectively coated to reduce the stagnation temperature to or less.


title: Solar thermal collector

text: In areas where freezing is a possibility, freeze-tolerance (the capability to freeze repeatedly without cracking) can be achieved by the use of flexible polymers. Silicone rubber pipes have been used for this purpose in UK since 1999. Conventional metal collectors are vulnerable to damage from freezing, so if they are water filled they must be carefully plumbed so they completely drain using gravity before freezing is expected so that they do not crack. Many metal collectors are installed as part of a sealed heat exchanger system. Rather than having potable water flow directly through the collectors, a mixture of water and antifreeze such as propylene glycol is used. A heat exchange fluid protects against freeze damage down to a locally determined risk temperature that depends on the proportion of propylene glycol in the mixture. The use of glycol lowers the water's heat carrying capacity marginally, while the addition of an extra heat exchanger may lower system performance at low light levels.


title: Solar thermal collector

text: A pool or unglazed collector is a simple form of flat-plate collector without a transparent cover. Typically, polypropylene or EPDM rubber or silicone rubber is used as an absorber. Used for pool heating, it can work quite well when the desired output temperature is near the ambient temperature (that is, when it is warm outside). As the ambient temperature gets cooler, these collectors become less effective.


title: Solar thermal collector

text: A "solar bowl" is a type of solar thermal collector that operates similarly to a parabolic dish, but instead of using a tracking parabolic mirror with a fixed receiver, it has a fixed spherical mirror with a tracking receiver. This reduces efficiency but makes it cheaper to build and operate. Designers call it a "fixed mirror distributed focus solar power system". The main reason for its development was to eliminate the cost of moving a large mirror to track the sun as with parabolic dish systems.


title: Solar thermal collector

text: A fixed parabolic mirror creates a variously shaped image of the sun as it moves across the sky. Only when the mirror is pointed directly at the sun does the light focus on one point. That is why parabolic dish systems track the sun. A fixed spherical mirror focuses the light in the same place independent of the sun's position. The light, however, is not directed to one point but is distributed on a line from the surface of the mirror to one half radius (along a line that runs through the sphere center and the sun).


title: Solar thermal collector

text: As the sun moves across the sky, the aperture of any fixed collector changes. This causes changes in the amount of captured sunlight, producing what is called the "sinus effect" of power output. Proponents of the solar bowl design claim the reduction in overall power output compared with tracking parabolic mirrors is offset by lower system costs.


title: Solar thermal collector

text: The sunlight concentrated at the focal line of a spherical reflector is collected using a tracking receiver. This receiver is pivoted around the focal line and is usually counterbalanced. The receiver may consist of pipes carrying fluid for thermal transfer or photovoltaic cells for direct conversion of light to electricity.


title: Solar thermal collector

text: The solar bowl design resulted from a project of the Electrical Engineering Department of the Texas Technical University, headed by Edwin O'Hair, to develop a 5 MWe power plant. A solar bowl was built for the town of Crosbyton, Texas as a pilot facility. The bowl had a diameter of , tilted at a 15° angle to optimize the cost/yield relation (33° would have maximized yield). The rim of the hemisphere was "trimmed" to 60°, creating a maximum aperture of . This pilot bowl produced electricity at a rate of 10 kW peak.


title: Solar thermal collector

text: A diameter Auroville solar bowl was developed from an earlier test of a bowl in 1979–1982 by the Tata Energy Research Institute. That test showed the use of the solar bowl in the production of steam for cooking. The full-scale project to build a solar bowl and kitchen ran from 1996 and was fully operational by 2001.


title: Solar thermal collector

text: In locations with average available solar energy, flat plate collectors are sized approximately 1.2 to 2.4 square decimeter per liter of one day's hot water use.


title: Solar thermal collector

text: The main use of this technology is in residential buildings where the demand for hot water has a large impact on energy bills. This generally means a situation with a large family or a situation in which the hot water demand is excessive due to frequent laundry washing. Commercial applications include laundromats, car washes, military laundry facilities and eating establishments. The technology can also be used for space heating if the building is located off-grid or if utility power is subject to frequent outages. Solar water heating systems are most likely to be cost effective for facilities with water heating systems that are expensive to operate, or with operations such as laundries or kitchens that require large quantities of hot water. Unglazed liquid collectors are commonly used to heat water for swimming pools but can also be applied to large-scale water pre-heating. When loads are large relative to the available collector area, the bulk of the water heating can be done at low temperature, lower than swimming pool temperatures where unglazed collectors are well established in the marketplace as the right choice. Because these collectors need not withstand high temperatures, they can use less expensive materials such as plastic or rubber. Many unglazed collectors are made of polypropylene and must be drained fully to avoid freeze damage when air temperatures drop below on clear nights. A smaller but growing percentage of unglazed collectors are flexible meaning they can withstand water freezing solid inside their absorber. The freeze concern only needs to be the water-filled piping and collector manifolds in a hard freeze condition. Unglazed solar hot water systems should be installed to "drainback" to a storage tank whenever solar radiation is insufficient. There are no thermal shock concerns with unglazed systems. Commonly used in swimming pool heating since solar energy's early beginnings, unglazed solar collectors heat swimming pool water directly without the need for antifreeze or heat exchangers. Hot water solar systems require heat exchangers due to contamination possibilities and in the case of unglazed collectors, the pressure difference between the solar working fluid (water) and the load (pressurized cold city water). Large-scale unglazed solar hot water heaters, like the one at the Minoru Aquatic Center in Richmond, BC operate at lower temperatures than evacuated tube or boxed and glazed collector systems. Although they require larger, more expensive heat exchangers, all other components including vented storage tanks and uninsulated plastic PVC piping reduce the costs of this alternative dramatically compared to the higher temperature collector types. When heating hot water, we are actually heating cold to warm and warm to hot. We can heat cold to warm as efficiently with unglazed collectors, just as we can heat warm to hot with high-temperature collectors.


title: Solar thermal collector

text: A simple solar air collector consists of an absorber material, sometimes having a selective surface, to capture radiation from the sun and transfers this thermal energy to air via conduction heat transfer. This heated air is then ducted to the building space or to the process area where the heated air is used for space heating or process heating needs. Functioning in a similar manner as a conventional forced-air furnace, solar-thermal-air systems provide heat by circulating air over an energy collecting surface, absorbing the sun’s thermal energy, and ducting air coming in contact with it. Simple and effective collectors can be made for a variety of air conditioning and process applications.


title: Solar thermal collector

text: Many applications can utilize solar air heat technologies to reduce the carbon footprint from the use of conventional heat sources, such as fossil fuels, to create a sustainable means to produce thermal energy. Applications such as space heating, greenhouse season extension, pre-heating ventilation makeup air, or process heat can be addressed by solar air heat devices. In the field of 'solar co-generation', solar thermal technologies are paired with photovoltaics (PV) to increase the efficiency of the system by taking heat away from the PV collectors, cooling the PV panels to improve their electrical performance while simultaneously warming air for space heating.


title: Solar thermal collector

text: Space heating for residential and commercial applications can be done through the use of solar air heating panels. This configuration operates by drawing air from the building envelope or from the outdoor environment and passing it through the collector where the air warms via conduction from the absorber and is then supplied to the living or working space by either passive means or with the assistance of a fan. A pioneering figure of this type of system was George Löf, who built a solar-heated air system in 1945 for a house in Boulder, Colorado. He later included a gravel bed for heat storage.


title: Solar thermal collector

text: Ventilation, fresh air or makeup air is required in most commercial, industrial and institutional buildings to meet code requirements. By drawing air through a properly designed unglazed transpired air collector or an air heater, the solar heated fresh air can reduce the heating load during daytime operation. Many applications are now being installed where the transpired collector preheats the fresh air entering a heat recovery ventilator to reduce the defrost time of HRV's. The higher your ventilation and temperature the better your payback time will be.


title: Solar thermal collector

text: Solar air heat is also used in process applications such as drying laundry, crops ("i.e". tea, corn, coffee) and other drying applications. Air heated through a solar collector and then passed over a medium to be dried can provide an efficient means by which to reduce the moisture content of the material.


title: Solar thermal collector

text: Offering the highest efficiency of any solar technology the through-pass configuration, air ducted onto one side of the absorber passes through a perforated material and is heated from the conductive properties of the material and the convective properties of the moving air. Through-pass absorbers have the most surface area which enables relatively high conductive heat transfer rates, but significant pressure drop can require greater fan power, and deterioration of certain absorber material after many years of solar radiation exposure can additionally create problems with air quality and performance.


title: Solar thermal collector

text: In back-pass, front-pass, and combination type configurations the air is directed on either the back, the front, or on both sides of the absorber to be heated from the return to the supply ducting headers. Although passing the air on both sides of the absorber will provide a greater surface area for conductive heat transfer, issues with dust (fouling) can arise from passing air on the front side of the absorber which reduces absorber efficiency by limiting the amount of sunlight received. In cold climates, air passing next to the glazing will additionally cause greater heat loss, resulting in lower overall performance of the collector.


title: Solar thermal collector

text: Glazed systems usually have a transparent top sheet and insulated side and back panels to minimize heat loss to ambient air. The absorber plates in modern panels can have absorptivity of more than 93%. Glazed Solar Collectors (recirculating types that are usually used for space heating). Air typically passes along the front or back of the absorber plate while scrubbing heat directly from it. Heated air can then be distributed directly for applications such as space heating and drying or may be stored for later use. Payback for glazed solar air heating panels can be less than 9–15 years depending on the fuel being replaced.


title: Solar thermal collector

text: Unglazed systems, or transpired air systems have been used to heat make-up or ventilation air in commercial, industrial, agriculture and process applications. They consist of an absorber plate which air passes across or through as it scrubs heat from the absorber. Non-transparent glazing materials are less expensive and decrease expected payback periods. Transpired collectors are considered "unglazed" because their collector surfaces are exposed to the elements, are often not transparent and not hermetically sealed.


title: Solar thermal collector

text: The term "unglazed air collector" refers to a solar air heating system that consists of a metal absorber without any glass or glazing over top. The most common type of unglazed collector on the market is the transpired solar collector. The technology has been extensively monitored by these government agencies, and Natural Resources Canada developed the feasibility tool RETScreen™ to model the energy savings from transpired solar collectors. Since that time, several thousand transpired solar collector systems have been installed in a variety of commercial, industrial, institutional, agricultural, and process applications in countries around the world. This technology was originally used primarily in industrial applications such as manufacturing and assembly plants where there were high ventilation requirements, stratified ceiling heat, and often negative pressure in the building. With the increasing drive to install renewable energy systems on buildings, transpired solar collectors are now used across the entire building stock because of high energy production (up to 750 peak thermal Watts/square metre), high solar conversion (up to 90%) and lower capital costs when compared against solar photovoltaic and solar water heating.


title: Solar thermal collector

text: Solar air heating is a renewable energy heating technology used to heat or condition air for buildings or process heat applications. It is typically the most cost-effective of all the solar technologies, especially in large scale applications, and it addresses the largest usage of building energy in heating climates, which is space heating and industrial process heating. They are either glazed or unglazed.


title: Solar thermal collector

text: Unglazed air collectors heat ambient (outside) air instead of recirculated building air. Transpired solar collectors are usually wall-mounted to capture the lower sun angle in the winter heating months as well as sun reflection off the snow and achieve their optimum performance and return on investment when operating at flow rates of between 4 and 8 CFM per square foot (72 to 144 m3/h.m2) of collector area.


title: Solar thermal collector

text: The exterior surface of a transpired solar collector consists of thousands of tiny micro-perforations that allow the boundary layer of heat to be captured and uniformly drawn into an air cavity behind the exterior panels. This heated ventilation air is drawn under negative pressure into the building’s ventilation system where it is then distributed via conventional means or using a solar ducting system.


title: Solar thermal collector

text: Hot air that may enter an HVAC system connected to a transpired collector that has air outlets positioned along the top of the collector, particularly if the collector is west facing. To counter this problem, Matrix Energy has patented a transpired collector with a lower air outlet position and perforated cavity framing to perpetrate increased air turbulence behind the perforated absorber for increased performance.


title: Solar thermal collector

text: This cutaway view shows the MatrixAir transpired solar collector components and air flow. The lower air inlet mitigates the intake of heated air to the HVAC system during summer operation.


title: Solar thermal collector

text: The extensive monitoring by Natural Resources Canada and NREL has shown that transpired solar collector systems reduce between 10-50% of the conventional heating load and that RETScreen is an accurate predictor of system performance.


title: Solar thermal collector

text: Transpired solar collectors act as a rainscreen and they also capture heat loss escaping from the building envelope which is collected in the collector air cavity and drawn back into the ventilation system. There is no maintenance required with solar air heating systems and the expected lifespan is over 30 years.


title: Solar thermal collector

text: Unglazed transpired collectors can also be roof-mounted for applications in which there is no suitable south-facing wall or for other architectural considerations. Matrix Energy Inc. has patented a roof-mounted product called the "Delta", a modular, roof-mounted solar air heating system where south-, east-, or west-facing facades are simply not available.


title: Solar thermal collector

text: Each ten-foot (3.05 m) module will deliver 250 CFM (425 m3/h)of preheated fresh air typically providing annual energy savings of 1100 kWh (4 GJ) annually. This unique two-stage, modular roof-mounted transpired collector operating a nearly 90% efficiency each module delivering over 118 L/s of preheated air per two square meter collector. Up to seven collectors may be connected in series in one row, with no limit to the number of rows connected in parallel along one central duct typically yielding 4 CFM of preheated air per square foot of available roof area.


title: Solar thermal collector

text: Transpired collectors can be configured to heat the air twice to increase the delivered air temperature making it suitable for space heating applications as well as ventilation air heating. In a 2-stage system, the first stage is the typical unglazed transpired collector and the second stage has glazing covering the transpired collector. The glazing allows all of that heated air from the first stage to be directed through a second set of transpired collectors for a second stage of solar heating.


title: Solar thermal collector

text: Parabolic troughs, dishes and towers described in this section are used almost exclusively in solar power generating stations or for research purposes. Parabolic troughs have been used for some commercial solar air conditioning systems. Although simple, these solar concentrators are quite far from the theoretical maximum concentration. For example, the parabolic trough concentration is about 1/3 of the theoretical maximum for the same acceptance angle, that is, for the same overall tolerances for the system. Approaching the theoretical maximum may be achieved by using more elaborate concentrators based on nonimaging optics. Solar thermal collectors may also be used in conjunction with photovoltaic collectors to obtain combined heat and power.


title: Solar thermal collector

text: This type of collector is generally used in solar power plants. A trough-shaped parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or heat pipe, placed at the focal point, containing coolant which transfers heat from the collectors to the boilers in the power station.


title: Solar thermal collector

text: With a parabolic dish collector, one or more parabolic dishes concentrate solar energy at a single focal point, similar to the way a reflecting telescope focuses starlight, or a dish antenna focuses radio waves. This geometry may be used in solar furnaces and solar power plants.


title: Solar thermal collector

text: The shape of a parabola means that incoming light rays which are parallel to the dish's axis will be reflected toward the focus, no matter where on the dish they arrive. Light from the sun arrives at the Earth's surface almost completely parallel, and the dish is aligned with its axis pointing at the sun, allowing almost all incoming radiation to be reflected towards the focal point of the dish. Most losses in such collectors are due to imperfections in the parabolic shape and imperfect reflection.


title: Solar thermal collector

text: Losses due to atmospheric scattering are generally minimal. However, on a hazy or foggy day, light is diffused in all directions through the atmosphere, which significantly reduces the efficiency of a parabolic dish. In dish stirling power plant designs, a stirling engine coupled to a dynamo is placed at the focus of the dish. This absorbs the energy focused onto it and converts it into electricity.


title: Solar thermal collector

text: A power tower is a large tower surrounded by tracking mirrors called heliostats. These mirrors align themselves and focus sunlight on the receiver at the top of the tower, collected heat is transferred to a power station below. This design reaches very high temperatures. High temperatures are suitable for electricity generation using conventional methods like steam turbine or a direct high-temperature chemical reaction such as liquid salt. By concentrating sunlight, current systems can get better efficiency than simple solar cells. A larger area can be covered by using relatively inexpensive mirrors rather than using expensive solar cells. Concentrated light can be redirected to a suitable location via optical fiber cable for such uses as illuminating buildings. Heat storage for power production during cloudy and overnight conditions can be accomplished, often by underground tank storage of heated fluids. Molten salts have been used to good effect. Other working fluids, such as liquid metals, have also been proposed due to their superior thermal properties.


title: Solar thermal collector

text: However, concentrating systems require sun tracking to maintain sunlight focus at the collector. They are unable to provide significant power in diffused light conditions. Solar cells are able to provide some output even if the sky becomes cloudy, but power output from concentrating systems drops drastically in cloudy conditions as diffused light cannot be concentrated well.


title: Dry eye syndrome

text: Dry eye syndrome (DES), also known as keratoconjunctivitis sicca (KCS), is the condition of having dry eyes. Other associated symptoms include irritation, redness, discharge, and easily fatigued eyes. Blurred vision may also occur. Symptoms range from mild and occasional to severe and continuous. Scarring of the cornea may occur in untreated cases.


title: Dry eye syndrome

text: Dry eye occurs when either the eye does not produce enough tears or when the tears evaporate too quickly. This can result from contact lens use, meibomian gland dysfunction, pregnancy, Sjögren syndrome, vitamin A deficiency, omega-3 fatty acid deficiency, LASIK surgery, and certain medications such as antihistamines, some blood pressure medication, hormone replacement therapy, and antidepressants. Chronic conjunctivitis such as from tobacco smoke exposure or infection may also lead to the condition. Diagnosis is mostly based on the symptoms, though a number of other tests may be used.


title: Dry eye syndrome

text: Treatment depends on the underlying cause. Artificial tears are usually the first line of treatment. Wrap-around glasses that fit close to the face may decrease tear evaporation. Stopping or changing certain medications may help. The medication ciclosporin or steroid eye drops may be used in some cases. Another option is lacrimal plugs that prevent tears from draining from the surface of the eye. Dry eye syndrome occasionally makes wearing contact lenses impossible.


title: Dry eye syndrome

text: Dry eye syndrome is a common eye disease. It affects 5–34% of people to some degree depending on the population looked at. Among older people it affects up to 70%. In China it affects about 17% of people. The phrase "keratoconjunctivitis sicca" means "dryness of the cornea and conjunctiva" in Latin


title: Dry eye syndrome

text: Typical symptoms of dry eye syndrome are dryness, burning and a sandy-gritty eye irritation that gets worse as the day goes on. Symptoms may also be described as itchy, stinging or tired eyes. Other symptoms are pain, redness, a pulling sensation, and pressure behind the eye. There may be a feeling that something, such as a speck of dirt, is in the eye. The resultant damage to the eye's surface increases discomfort and sensitivity to bright light. Both eyes usually are affected.


title: Dry eye syndrome

text: There may also be a stringy discharge from the eyes. Although it may seem contradictory, dry eye can cause the eyes to water due to irritation. One may experience excessive tearing such as if something got into the eye. These reflex tears will not necessarily make the eyes feel better since they are the watery tears that are produced in response to injury, irritation, or emotion which lack the lubricating qualities necessary to prevent dry eye.


title: Dry eye syndrome

text: Because blinking coats the eye with tears, symptoms are worsened by activities in which the rate of blinking is reduced due to prolonged use of the eyes. These activities include prolonged reading, computer usage (computer vision syndrome), driving, or watching television. Symptoms increase in windy, dusty or smoky (including cigarette smoke) areas, in dry environments high altitudes including airplanes, on days with low humidity, and in areas where an air conditioner (especially in a car), fan, heater, or even a hair dryer is being used. Symptoms reduce during cool, rainy, or foggy weather and in humid places, such as in the shower.


title: Dry eye syndrome

text: Most people who have dry eyes experience mild irritation with no long-term effects. However, if the condition is left untreated or becomes severe, it can produce complications that can cause eye damage, resulting in impaired vision or (rarely) in the loss of vision.


title: Dry eye syndrome

text: Symptom assessment is a key component of dry eye diagnosis – to the extent that many believe dry eye syndrome to be a symptom-based disease. Several questionnaires have been developed to determine a score that would allow for a diagnosis. The McMonnies & Ho dry eye questionnaire is often used in clinical studies of dry eyes.


title: Dry eye syndrome

text: Any abnormality of any one of the three layers of tears produces an unstable tear film, resulting in symptoms of dry eyes.


title: Dry eye syndrome

text: The most common cause of dry eye is increased evaporation of the tear film, typically as a result of Meibomian gland dysfunction. The meibomian glands are two sets of oil glands that line the upper and lower eyelids and secrete the oily outer layer of the tear film—the lipid layer. These glands often become clogged due to inflammation caused by blepharitis and/or rosacea, preventing an even distribution of oil. The result is an unstable lipid layer that leads to increased evaporation of the tear film.


title: Dry eye syndrome

text: Keratoconjunctivitis sicca can be caused by inadequate tear production from lacrimal hyposecretion. The aqueous tear layer is affected, resulting in aqueous tear deficiency (ATD). The lacrimal gland does not produce sufficient tears to keep the entire conjunctiva and cornea covered by a complete layer. This usually occurs in people who are otherwise healthy. Increased age is associated with decreased tearing. This is the most common type found in postmenopausal women.


title: Dry eye syndrome

text: In many cases, aqueous deficient dry eye may have no apparent cause (idiopathic). Other causes include congenital alacrima, xerophthalmia, lacrimal gland ablation, and sensory denervation. In rare cases, it may be a symptom of collagen vascular diseases, including relapsing polychondritis, rheumatoid arthritis, granulomatosis with polyangiitis, and systemic lupus erythematosus. Sjögren syndrome and other autoimmune diseases are associated with aqueous tear deficiency. Drugs such as isotretinoin, sedatives, diuretics, tricyclic antidepressants, antihypertensives, oral contraceptives, antihistamines, nasal decongestants, beta-blockers, phenothiazines, atropine, and pain relieving opiates such as morphine can cause or worsen this condition. Infiltration of the lacrimal glands by sarcoidosis or tumors, or postradiation fibrosis of the lacrimal glands can also cause this condition. Recent attention has been paid to the composition of tears in normal or dry eye individuals. Only a small fraction of the estimated 1543 proteins in tears are differentially deficient or upregulated in dry eye, one of which is lacritin. Topical lacritin promotes tearing in rabbit preclinical studies. Also, topical treatment of eyes of dry eye mice (Aire knockout mouse model of dry eye) restored tearing, and suppressed both corneal staining and the size of inflammatory foci in lacrimal glands.


title: Dry eye syndrome

text: Aging is one of the most common causes of dry eyes because tear production decreases with age. Several classes of medications (both prescription and OTC) have been hypothesized as a major cause of dry eye, especially in the elderly. Particularly, anticholinergic medications that also cause dry mouth are believed to promote dry eye. Dry eye may also be caused by thermal or chemical burns, or (in epidemic cases) by adenoviruses. A number of studies have found that diabetics are at increased risk for the disease.


title: Dry eye syndrome

text: About half of all people who wear contact lenses complain of dry eyes. There are two potential connections between contact usage and dry eye. Traditionally, it was believed that soft contact lenses, which float on the tear film that covers the cornea, absorb the tears in the eyes. The connection between a loss in nerve sensitivity and tear production is also the subject of current research.


title: Dry eye syndrome

text: Dry eye also occurs or becomes worse after LASIK and other refractive surgeries, in which the corneal nerves which stimulate tear secretion are cut during the creation of a corneal flap. Dry eye caused by these procedures usually resolves after several months, but it can be permanent. Persons who are thinking about refractive surgery should consider this.


title: Dry eye syndrome

text: An eye injury or other problem with the eyes or eyelids, such as bulging eyes or a drooping eyelid can cause keratoconjunctivitis sicca. Disorders of the eyelid can impair the complex blinking motion required to spread tears.


title: Dry eye syndrome

text: Abnormalities of the mucin tear layer caused by vitamin A deficiency, trachoma, diphtheric keratoconjunctivitis, mucocutaneous disorders and certain topical medications are also causes of keratoconjunctivitis sicca.


title: Dry eye syndrome

text: Persons with keratoconjunctivitis sicca have elevated levels of tear nerve growth factor (NGF). It is possible that this eye's surface NGF plays an important role in ocular surface inflammation associated with dry eyes.


title: Dry eye syndrome

text: Having dry eyes for a while can lead to tiny abrasions on the surface of the eyes. In advanced cases, the epithelium undergoes pathologic changes, namely squamous metaplasia and loss of goblet cells. Some severe cases result in thickening of the corneal surface, corneal erosion, punctate keratopathy, epithelial defects, corneal ulceration (sterile and infected), corneal neovascularization, corneal scarring, corneal thinning, and even corneal perforation.


title: Dry eye syndrome

text: Another contributing factor may be lacritin monomer deficiency. Lacritin monomer, active form of lacritin, is selectively decreased in aqueous deficient dry eye, Sjögren syndrome dry eye, contact lens-related dry eye and in blepharitis.


title: Dry eye syndrome

text: Some tests allow patients to be classified into one of two categories, “aqueous-deficient” or “hyperevaporative.” Diagnostic guidelines were published in 2007 by the Dry Eye Workshop. A slit lamp examination can be performed to diagnose dry eyes and to document any damage to the eye. When realizing this test, the practitioner is testing the eyelid margin.


title: Dry eye syndrome

text: A Schirmer's test can measure the amount of moisture bathing the eye. This test is useful for determining the severity of the condition. A five-minute Schirmer's test with and without anesthesia using a Whatman #41 filter paper 5 mm wide by 35 mm long is performed. For this test, wetting under 5 mm with or without anesthesia is considered diagnostic for dry eyes.


title: Dry eye syndrome

text: If the results for the Schirmer's test are abnormal, a Schirmer II test can be performed to measure reflex secretion. In this test, the nasal mucosa is irritated with a cotton-tipped applicator, after which tear production is measured with a Whatman #41 filter paper. For this test, wetting under 15 mm after five minutes is considered abnormal.


title: Dry eye syndrome

text: A tear breakup time (TBUT) test measures the time it takes for tears to break up in the eye. The tear breakup time can be determined after placing a drop of fluorescein in the cul-de-sac.


title: Dry eye syndrome

text: A tear protein analysis test measures the lysozyme contained within tears. In tears, lysozyme accounts for approximately 20 to 40 percent of total protein content.


title: Dry eye syndrome

text: The presence of the recently described molecule Ap4A, naturally occurring in tears, is abnormally high in different states of ocular dryness. This molecule can be quantified biochemically simply by taking a tear sample with a plain Schirmer test. Utilizing this technique it is possible to determine the concentrations of Ap4A in the tears of patients and in such way diagnose objectively if the samples are indicative of dry eye.


title: Dry eye syndrome

text: The tear osmolarity test has been proposed as a test for dry eye disease. Tear osmolarity may be a more sensitive method of diagnosing and grading the severity of dry eye compared to corneal and conjunctival staining, tear break-up time, Schirmer test, and meibomian gland grading. Others have recently questioned the utility of tear osmolarity in monitoring dry eye treatment.


title: Dry eye syndrome

text: Avoiding refractive surgery (LASIK & PRK), limiting contact lens use, limiting computer screen use, avoiding environmental conditions can decrease symptoms. Complications can be prevented by use of wetting and lubricating drops and ointments.


title: Dry eye syndrome

text: A variety of approaches can be taken to treatment. These can be summarised as: avoidance of exacerbating factors, tear stimulation and supplementation, increasing tear retention, and eyelid cleansing and treatment of eye inflammation.


title: Dry eye syndrome

text: Dry eyes can be exacerbated by smoky environments, dust and air conditioning and by our natural tendency to reduce our blink rate when concentrating. Purposefully blinking, especially during computer use and resting tired eyes are basic steps that can be taken to minimise discomfort. Rubbing one's eyes can irritate them further, so should be avoided. Conditions such as blepharitis can often co-exist and paying particular attention to cleaning the eyelids morning and night with mild soaps and warm compresses can improve both conditions.


title: Dry eye syndrome

text: Dry, drafty environments and those with smoke and dust should be avoided. This includes avoiding hair dryers, heaters, air conditioners or fans, especially when these devices are directed toward the eyes. Wearing glasses or directing gaze downward, for example, by lowering computer screens can be helpful to protect the eyes when aggravating environmental factors cannot be avoided. Using a humidifier, especially in the winter, can help by adding moisture to the dry indoor air.


title: Dry eye syndrome

text: Application of artificial tears every few hours can provide temporary relief. Additional research is necessary to determine whether certain artificial tear formulations are superior to others in treating dry eye.


title: Dry eye syndrome

text: A 2017 Cochrane review found mixed results when comparing autologous serum eye drops to artificial tears or saline. Evidence from the examined trials showed that autologous serum eye drops may have a small short-term benefit when compared to artificial tears, but there is no evidence of improvement after 2 weeks.


title: Dry eye syndrome

text: Lubricating tear ointments can be used during the day, but they generally are used at bedtime due to poor vision after application. They contain white petrolatum, mineral oil, and similar lubricants. They serve as a lubricant and an emollient. Application requires pulling down the lower eyelid and applying a small amount (0.25 in) inside. Depending on the severity of the condition, it may be applied from every hour to just at bedtime. It should never be used with contact lenses. Specially designed glasses that form a moisture chamber around the eye may be used to create additional humidity.


title: Dry eye syndrome

text: Inflammation occurring in response to tears film hypertonicity can be suppressed by mild topical steroids or with topical immunosuppressants such as ciclosporin (Restasis). Elevated levels of tear NGF can be decreased with 0.1% prednisolone.


title: Dry eye syndrome

text: Diquafosol, an agonist of the P2Y purinergic receptor, is approved in Japan for managing dry eye disease by promoting secretion of fluid and mucin from cells in the conjunctiva, rather than by directly stimulating the lacrimal glands.


title: Dry eye syndrome

text: Varenicline (Tyrvaya by Oyster Point Pharma) was approved by the US FDA for the treatment of dry eye disease in October 2021.


title: Dry eye syndrome

text: Topical ciclosporin (topical ciclosporin A, tCSA) 0.05% ophthalmic emulsion is an immunosuppressant. The drug decreases surface inflammation. In a trial involving 1200 people, Restasis increased tear production in 15% of people, compared to 5% with placebo.


title: Dry eye syndrome

text: It should not be used while wearing contact lenses, during eye infections or in people with a history of herpes virus infections. Side effects include burning sensation (common), redness, discharge, watery eyes, eye pain, foreign body sensation, itching, stinging, and blurred vision. Long term use of ciclosporin at high doses is associated with an increased risk of cancer.


title: Dry eye syndrome

text: In each eye, there are two puncta – little openings that drain tears into the tear ducts. There are methods to partially or completely close the tear ducts. This blocks the flow of tears into the nose, and thus more tears are available to the eyes. Drainage into either one or both puncta in each eye can be blocked.


title: Dry eye syndrome

text: Punctal plugs are inserted into the puncta to block tear drainage. It is not clear if punctal plugs are effective at reducing dry eye syndrome symptoms. Punctal plugs are thought to be "relatively safe", however, their use may result in epiphora (watery eyes), and more rarely, serious infection and swelling of the tear sac where the tears drain. They are reserved for people with moderate or severe dry eye when other medical treatment has not been adequate.


title: Dry eye syndrome

text: If punctal plugs are effective, thermal or electric cauterization of puncti can be performed. In thermal cauterization, a local anesthetic is used, and then a hot wire is applied. This shrinks the drainage area tissues and causes scarring, which closes the tear duct.


title: Dry eye syndrome

text: Heating systems that try to unblock the oil glands in the eye has some preliminary evidence of benefit. Fish- flax- and hemp-oil (omega-3) supplements are not effective in relieving symptoms.


title: Dry eye syndrome

text: In severe cases of dry eyes, tarsorrhaphy may be performed where the eyelids are partially sewn together. This reduces the palpebral fissure (eyelid separation), ideally leading to a reduction in tear evaporation.


title: Dry eye syndrome

text: Keratoconjunctivitis sicca usually is a chronic problem. Its prognosis shows considerable variance, depending upon the severity of the condition. Most people have mild-to-moderate cases, and can be treated symptomatically with lubricants. This provides an adequate relief of symptoms.


title: Dry eye syndrome

text: When dry eyes symptoms are severe, they can interfere with quality of life. People sometimes feel their vision blurs with use, or severe irritation to the point that they have trouble keeping their eyes open or they may not be able to work or drive.


title: Dry eye syndrome

text: Keratoconjunctivitis sicca is relatively common within the United States, especially so in older patients. Specifically, the persons most likely to be affected by dry eyes are those aged 40 or older. 10–20% of adults experience Keratoconjunctivitis sicca. Approximately 1 to 4 million adults (age 65–84) in the USA are affected.


title: Dry eye syndrome

text: While persons with autoimmune diseases have a high likelihood of having dry eyes, most persons with dry eyes do not have an autoimmune disease. Instances of Sjögren syndrome and keratoconjunctivitis sicca associated with it are present much more commonly in women, with a ratio of 9:1. In addition, milder forms of keratoconjunctivitis sicca also are more common in women. This is partly because hormonal changes, such as those that occur in pregnancy, menstruation, and menopause, can decrease tear production.


title: Dry eye syndrome

text: In areas of the world where malnutrition is common, vitamin A deficiency is a common cause. This is rare in the United States.


title: Dry eye syndrome

text: Other names for dry eye include dry eye syndrome, keratoconjunctivitis sicca (KCS), dysfunctional tear syndrome, lacrimal keratoconjunctivitis, evaporative tear deficiency, aqueous tear deficiency, and LASIK-induced neurotrophic epitheliopathy (LNE).


title: Dry eye syndrome

text: Keratoconjunctivitis sicca is common in dogs. Most cases are caused by a genetic predisposition, but chronic conjunctivitis, canine distemper, and drugs such as sulfasalazine and trimethoprim-sulfonamide also cause the disease. Symptoms include eye redness, a yellow or greenish discharge, corneal ulceration, pigmented cornea, and blood vessels on the cornea. Diagnosis is made by measuring tear production with a Schirmer tear test. Less than 15 mm of wetting by tears produced in a minute is abnormal.


title: Dry eye syndrome

text: Tear replacers are a mainstay of treatment, preferably containing methylcellulose or carboxymethyl cellulose. Ciclosporin stimulates tear production and acts as a suppressant on the immune-mediated processes that cause the disease. Topical antibiotics and corticosteroids are sometimes used to treat secondary infections and inflammation. A surgery known as parotid duct transposition is used in some extreme cases where medical treatment has not helped. This redirects the duct from the parotid salivary gland to the eye. Saliva replaces the tears. Dogs with cherry eye should have the condition corrected to help prevent this disease.


title: Dry eye syndrome

text: Keratoconjunctivitis sicca is uncommon in cats. Most cases seem to be caused by chronic conjunctivitis, especially secondary to feline herpesvirus. Diagnosis, symptoms, and treatment are similar to those for dogs.


title: Frederic Remington

text: Frederic Sackrider Remington (October 4, 1861 – December 26, 1909) was an American painter, illustrator, sculptor, and writer who specialized in the genre of Western American Art. His works are known for depicting the Western United States in the last quarter of the 19th century and featuring such images as cowboys, American Indians, and the US Cavalry.


title: Frederic Remington

text: Remington was born in Canton, New York, in 1861 to Seth Pierrepont Remington (1830–1880) and Clarissa (Clara) Bascom Sackrider (1836–1912).


title: Frederic Remington

text: His paternal family owned hardware stores and emigrated from Alsace-Lorraine in the early 18th century. His maternal family, of French Basque ancestry, came to America in the early 1600s and founded Windsor, Connecticut. Remington's father was a Union army colonel in the American Civil War, whose family had arrived in America from England in 1637. He was a newspaper editor and postmaster, and the staunchly Republican family was active in local politics. The Remingtons were horsemen. One of Remington's great-grandfathers, Samuel Bascom, was a saddle maker by trade. Remington's ancestors also fought in the French and Indian War, the American Revolution, and the War of 1812.