Operating circuit and method for remanent reed relays
United States Patent 1 1 1111 3,879,643 Hubbard 1 5] Apr. 22, 1975 1 1 OPERATING CIRCUIT ANI) METHOD FOR 3.274.452 9/1966 Landes 317/1575 REMANENT REED RELAYS 3.376.477 4/1968 Weingcr 3l7/l55.5  
 [75] Inventor: Linus O. Hubbard, Chicago. 111.  
  Primary l:.\&#39;1mmer-L. T. Hlx [73] ssignee hon d C0&#34; -1 cago. 1 Artur/1e Agent. or Firn1Mas0n, Kolehmainen. 221 Filed: Dec. 13, 1973 [2]] Appl. No.: 424,567  
 [ ABSTRACT 52 us. c1. 317/1575 A remanem reed relay is Operated by magnetizing a 151 1111. C1. H0lf 13/00 reed Switch with a DC Current in Opeming Wind- [58] Field of Search 317/1555. 157.5 mg and by demagnetilifig the reed Switch with damped oscillation in the operating winding. The [56] References Cited winding is an inductance in the tuned circuit of an os- UNITED STATES PATENTS cillator producing the damped oscillation.  
 2.441.984 5/1948 Armstrong 317/1575 20 Claims, 1 Drawing Figure Q1) 10 I4 TURN ON f l PULSE SOURCE /:l: T 58 36 TURN OFF 9 34 PULSE SOURCE 16 CONTROLLED CIRCUIT PATENlEnAPazzlvs 3.879.643  
  TURN ON PULSE SOURCE TUR N OFF PULSE SOURCE CONTROLLED CIRCUIT OPERATING CIRCUIT AND METHOD FOR REMANENT REED RELAYS The present invention relates to improvements in circuits and methods for operating latching remanent reed relays.  
  Reed relays typically include a reed switch operated between closed and open positions by magnetic fields produced by one or more windings. A latching reed relay includes reeds fabricated of high remanence magnetizable material. Residual magnetization of the reeds following operation latches the switch by maintaining the reeds in position until the next operation of the switch. The switch may be magnetically latched in both closed and open positions, or may be magnetically latched in one position and demagnetized and maintained in the other, normal position by spring force of the reeds.  
  Several arrangements are used for operating remanent reed relays. The simplest uses one or a pair of operating coils surrounding both reeds, and DC current is used to develop a magnetic field in one direction to magnetize the reeds and to develop an opposite magnetic field to demagnetize the reeds. One difficulty with this approach is that the strength of the demagnetizing field must be carefully controlled within close limits to assure sufficient demagnetization while avoiding magnetization of the reeds in the opposite direction.  
  Another approach is to use one or a pair of coils adjacent to each reed a total of two or four coils. Each reed is independently magnetized in either desired direction to achieve latched open and latched closed conditions. Difficulties arise in that the windings must be carefully aligned with the reeds. The coefficient of coupling between adjacent coils must be kept to a minimum. and this places limitations on the size and shape of the coils. Such coil arrays are difficult to manufacture and to successfully operate. particularly where small reed switches are used and where operating voltages and currents are limited.  
  A primary object of the present invention is to provide improvements in operating circuits for remanent reed relays and to overcome disadvantages of known arrangements. Other important objects are to provide remanent reed relay operating circuits characterized by simple and easily manufactured coil arrangements, by reliability in operation even at relatively low voltage and current levels and with miniature reed switch devices, and by ease of design in that close tolerances in operating conditions and physical characteristics are not imposed.  
  In brief, in accordance with the invention there is provided a latching remanent reed relay operating circuit wherein magnetization of the reeds is accomplished by a DC current and wherein demagnetization is accomplished by a damped oscillation in a winding adjacent the reeds. Another feature of the invention resides in the use of the winding as an inductance in the oscillator. In addition, in accordance with the invention the oscillator may be squegging the produce the damped oscillation at the earliest possible moment.  
  The invention and the above and other objects and advantages can be best understood from the following detailed description of the embodiment of the invention illustrated in the accompanying drawing.  
  The single FIGURE of the drawing is a schematic and block diagram of a remanent reed relay operating circuit constructed in accordance with the principles of the invention.  
  In the drawing the reference numeral 10 generally designates a remanent reed relay operating circuit embodying the features of the present invention. The circuit 10 controls the operation ofa remanent reed relay 12 in accordance with control signals received from a turn on pulse source 14 and a turn off pulse source 16 thereby to control the operation of a controlled circuit 18.  
  Relay 12 is a latching reed relay and in the illustrated embodiment includes a reed switch 20 controlled by a winding 22. Switch 20 may be a conventional device including an evacuated envelope 24 enclosing a pair of reed contacts 26 and 28 formed of flexible, resilient conductive material and disposed in a normally open configuration with the reed contact portions separated. Reeds 26 and 28 exhibit high magnetic remanence, and the reed switch can be latched in either its open circuit or closed circuit condition by magnetization of the reeds 26 and 28 in the corresponding magnetic orientation. One example of a latching remanent reed switch is the model MSLS-2 reed switch available from Hamlin lnc. of Lake Mills, Wisconsin.  
  Operation of the reed switch is controlled by winding 22. The winding is magnetically coupled to reeds 26 and 28. In accordance with conventional practice the winding may encircle the envelope 24, for example by being wound around a bobbin surrounding the switch 20. As described in greater detail below, the operating circuit is effective to close the reed switch by energizing the winding 22 with a DC current. This generates a unidirectional magnetic field aligned with reeds 26 and 28 and each reed is magnetized with opposite poles adjacent. Consequently, the reeds move into contact with one another. and remain latched in this position due to residual magnetism maintained in the remanent reed material.  
  In accordance with an important feature of the invention, the reed switch is operated from its closed position to its open position by demagnetizing the reeds in a novel manner. In accordance with the invention, the operating circuit 10 includes an oscillator generally designated as 30, and the oscillator 30 is controlled in order to effect demagnetization of reeds 26 and 28 by subjecting the reeds to a damped oscillation. Yet another important feature of the invention resides in the use of the winding 22 for two functions both as the source of the magnetic field to which the reed switch 20 is subjected, and as an inductance in the oscillator 30.  
  Proceeding now to a more detailed description of the structure and operation of the circuit 10, in the illustrated arrangement the relay 12 controls the energization of controlled circuit 18 from a power supply comprising a relatively positive terminal and reference or ground terminal. Circuit 18 is shown in block form and may comprise any of a wide variety of electrically operated or controlled circuits or devices. Moreover, the relay 12 may carry out any desired control function including but not limited to the illustrated function of interconnecting circuit 18 with a power source.  
  In the illustrated arrangement the operating circuit 10 is controlled by the pair of pulse sources 14 and 16. Each source normally has a relatively positive output voltage, and this output voltage is reduced in order to perform a control function. When it is desired to energize or turn on the controlled circuit 18, the turn on source 14 is operated to supply a relatively negative pulse to the circuit in order to energize relay 12. Conversely, to deenergize or turn off the controlled circuit 18, the turn off source 16 is operated to supply a relatively negative pulse to the circuit 10 in order to operate relay 12 to its open circuit condition. Pulse sources&#34; 14 and 16 may be of any desired type and for example might comprise logic circuitry or might be as simple as a pair of manually operated, normally open, momentary contact switches connected between the circuit 10 and a point of ground or reference potential.  
  In order to permit the relay 12 to be controlled by pulse signals, the circuit 10 includes a switching section generally designated as 32 and including a pair of switching transistors 34 and 36. Each transistor 34 and 36 is normally maintained in a nonconductive condition by connection of its emitter electrode to a source of relatively positive potential and connection of its base electrode to the output of the corresponding pulse source 14 or 16. In order to operate the relay 12 to its closed circuit condition, source 14 applies a negative pulse to the base electrode of transistor 36 to place this transistor in a conductive condition. Similarly a negative pulse is applied by source 16 to the base electrode of transistor 34 to render this transistor conductive, thereby to energize oscillator 30 and operate relay 12 to its open circuit condition.  
  Should pulse control not be required, the pulse sources 14 and 16 together with the switching section 32 may be omitted. More specifically, transistors 34 and 36 may be replaced with any desired type of manual or other switching device for selectively completing circuits to the relay 12 and oscillator 30.  
  With reference now more specifically to the turn on function, as indicated above the reeds 26 and 28 are closed and magnetized by the application of a DC current to the winding 22. In the illustrated arrangement winding 22 includes a pair of end terminals 38 and 40 as well as an intermediate tap terminal 42 subdividing the winding 22 into two winding portions 22A and 228. When switching transistor 36 is rendered conductive, DC current flows from the source of positive potential through transistor 36, a current limiting resistor 44, winding portion 22A, and to ground through tap 42. This DC current creates a magnetic field for closing and latching reed contacts 26 and 28. The contacts remain closed due to remanence of reeds 26 and 28 until reopened by the operating circuit 10.  
  In accordance with the invention, the turn off function is performed in a novel fashion by the oscillator 30. An oscillator transistor 46 includes an emitter electrode coupled to the collector electrode of switching transistor 34, and the oscillator 30 is normally deenergized as transistor 34 is maintained in a nonconductive condition. Base electrode bias for oscillator transistor 46 is supplied by a voltage divider including resistors 48 and 50 and the oscillator 30 is energized when transistor 34 is rendered conductive by the application of rel- ,atively&#39;positive voltage to the voltage divider and to the emitter electrode of transistor 46.  
 lation is supplied by including winding portion 22B in the base electrode circuit of the oscillator transistor 46.  
 Winding portion 22B is magnetically coupled to portion 22A and provides a convenient arrangement. 5 However, if desired a separate tickler coil winding or other conventional means could be used to provide positive feedback.  
  Oscillator 30 is energized upon operation of turn off switching transistor.34, and as a result an oscillating current flows in winding portion 22A. This current induces an oscillating magnetic field applied to the remanent reed contacts 26 and 28. In accordance with an important feature of the invention, reeds 26 and 28 are demagnetized by damping the oscillations produced by the oscillator 30 to the end that the damped oscillations produce a continuously decreasing alternating magnetic field applied to reeds 26 and 28. This alternating magnetic field decreases until it has completely died away to zero field strength.  
  Damping of the oscillations in winding portion 22A may be accomplished in accordance with this feature of the invention simply by deenergizing the oscillator 30. For example, at the end of the pulse supplied by source 16, transistor 34 returns to its nonconductive condition and the circuit for energization of transistor 46 is interrupted. Consequently, oscillations diminish over a period of time to produce the desired damped wave. Although this approach is satisfactory for many purposes, it results in a delay because the oscillations are not damped until after the oscillator is deenergized. In order to avoid this delay, an alternative method is employed in the illustrated embodiment of the invention.  
  More specifically, in accordance with a further feature of the invention the oscillator is squegging in operation. A coupling capacitor 54 supplies positive feedback from the winding 22B to the base of transistor 46. Capacitor 54 is made large so that its discharge time through resistors 48 and 56 is many times the period of a single cycle of the oscillator frequency. Consequently, as soon as oscillator 30 is energized, oscillation starts and capacitor 54 receives a charge at each peak of the oscillation cycle when substantial conduction occurs from the emitter to the base of the oscillator transistor 46. After one or two cycles of the oscillation, capcitor 54 becomes charged, so that transistor 46 is biased in a nonconductive condition and the oscillations die away with a gradually diminishing amplitude. Oscillation does not start again until capacitor 54 has become discharged through resistors 48 and 56, and transistor 46 has returned to normal bias. If the turn-off pulse is short, only a single damped oscillation will occur. If the turn-off signal is long or continuous, a train of damped oscillations will occur. The advantage of the squegging oscillator is that the first damped oscillation starts at the time the oscillator is energized rather than being delayed until the oscillator is deenergized.  
  It is desirable to assure that oscillations do not take place during turn-on operation, as such oscillations when discontinued would interfere with or prevent the desired magnetization of the reeds 26 and 28. In accordance with a feature of the invention, the oscillator tuned circuit is disabled during turn-on so that current flow in winding 22 cannot cause undesired oscillation.  
  More specifically, during the turn-off operation, the capacitor 52 is effectively connected across winding portion 22A by conductive switch transistor 34. Portion 22A is onnected between terminal 38 and ground. Capacitor 52 is connected between terminal 38 and ground by a circuit including transistor 34 and capacitor 58. Capacitor 58 is part of a conventional power supply circuit not otherwise illustrated and exhibits a&#39; low impedance to signals at the oscillator frequency. During turn-on operation, transistor 34 is in a nonconductive condition and interrupts the connection between capacitor 52 and ground thus disabling the oscillator tuned circuit and preventing oscillations in the tuned circuit.  
  ln the illustrated embodiment of the invention, components of the oscillator 30 perform other desirable functions both during turn-on and turn-off operations. During turn-on operation, resistor 56 and capacitor 52 are connected in series across the entire winding 22 in order to load the winding and prevent ringing, and to absorb inductive kick.  
  During turn-off, a DC current of relatively small magnitude flows from a point of relatively positive potential to ground through a circuit including transistor 34, resistor 56 and winding portion 228. This arrangement has two important advantages. First, the DC current flow through winding portion 228 induces a demagnetizing magnetic field which, although substantially less strong than the turn-on field, assists the damped oscillation effect in demagnetizing reeds 26 and 28. In addition, the steady state DC current flow through transistor 34 improves the&#39;ability of the transistor to couple oscillating signals to ground from the capacitor 52.  
  In a device constructed in accordance with the present invention, the following component values were used:  
 .22 microfarads 4 microfarads l000 microfarads Type MPSA56 Capacitor 52 Capacitor 56 Capacitor 58 Transistors The device operated properly and achieved both turn-on and turn-off functions reliably. The oscillator 30 oscillated at approximately 3,300 Hertz, and squegged at approximately 130 Hertz. These values are provided as an illustration of one specific embodiment of the invention, and should not be considered to limit the scope of the invention.  
  Although the invention has been described with reference to details of the illustrated embodiment, such details should not be taken to limit the invention as defined in the following claims.  
  What is claimed and desired to be secured by Letters Patent of the United States is:  
  l. A circuit for demagnetizing a remanent reed of a reed switch comprising:  
 a winding means magnetically associated with said reed switch;  
 an oscillator coupled to said winding means; and  
 means for damping the oscillations of said oscillator for producing an alternating and diminishing magnetic field in the vicinity of said reed switch.  
  2. The circuit of claim 1, said oscillator including a tuned circuit, and said winding means constituting an inductance in said tuned circuit.  
 .in said output circuit.  
  4. The circuit of claim 3, an additional winding means in said input circuit and magnetically coupled to said first winding means.  
  5. The circuit of claim 4, an operating coil surrounding the reed switch, said first and said additional winding means comprising segments of said coil.  
  6. The circuit of claim 1, said damping means comprising switching means for deenergizing said oscillatOl&#39;.  
  7. The circuit of claim 1, said damping means comprising means for squegging said oscillator.  
  8. A circuit for operating a latching reed switch including at least one remanent reed, said circuit including:  
 winding means disposed adjacent the reed;  
 first circuit means coupled to said winding means for passing a DC current through said winding means for magnetizing the reed; and  
 second circuit means coupled to said winding means for passing a damped oscillatory wave train through said winding means for demagnetizing said reed.  
  9. The circuit of claim 8, further comprising third circuit means operable simultaneously with said second circuit means for passing a DC current through said winding means of a polarity opposite to said magnetizing DC current.  
  10. The circuit of claim 8, said second circuit means including an oscillator having a tuned circuit, said winding means comprising an inductance in said tuned circuit.  
  11. The circuit of claim 10 further comprising first switching means for controlling the energization of said first circuit means, and second switching means for controlling the energization of said second circuit means.  
  12. The circuit of claim 10, further comprising means for disabling said tuned circuit during operation of said first circuit means.  
  13. An operating circuit for a relay including a remanent reed switch, said operating circuit comprising:  
 a DC power supply having first and second terminals;  
 an operating winding for applying induced magnetic fields to the reed switch;  
 said winding including two winding portions;  
 a first circuit including one winding portion connected between said power supply terminals and including first switching means for energizing said one winding portion with a DC current;  
 a squegging oscillator having a tuned circuit including said one winding portion; and  
 second switching means coupled between said power supply and said oscillator for energizing said oscillator for energizing said one winding portion with a damped oscillation.  
 14. The circuit of claim 13, said oscillator including a feedback circuit including the other said winding portion.  
  15. The circuit of claim 14, said tuned circuit including a capacitor coupled across said one winding portion through said second switching means.  
  16. The circuit of claim 15, said oscillator including a transistor with said feedback circuit coupled to its 18. A method for demagnetizing a remanent reed of a reed relay comprising:  
 developing a damped oscillation in the winding of the relay.  
  19. A method as claimed in claim 18 wherein said developing step comprises generating an oscillating signal with anoscillator, and deenergizing said oscillator.  
  20. A method as claimed in claim 18 wherein said developing step comprises generating an oscillating signal with an oscillator, and squegging said oscillator.