Electrochemical sensor elements are used in laboratory and process measurement technology in many areas of chemistry, biochemistry, pharmacy, biotechnology, food technology, water management, and environmental monitoring for the analysis of measuring media—in particular, of measuring liquids. Electrochemical measuring techniques allow detection of, for example, activities of chemical substances, such as ions, and of a therewith-correlated process variable of an—in particular, liquid—measuring medium. The substance whose concentration or activity is to be measured is also referred to as analyte. Electrochemical sensor elements may, for example, be potentiometric or amperometric sensor elements.
Potentiometric sensor elements typically comprise a measuring half-cell and a reference half-cell, as well as a measurement circuit. The measuring half-cell includes a potential-forming element, which may comprise, for example, a redox electrode, an analyte-sensitive coating, or an ion-selective membrane, depending upon the type of potentiometric sensor element. The measurement circuit generates a measurement signal that represents the potential difference between the measuring half-cell and the reference half-cell. Examples of potentiometric sensor elements are ion-selective electrodes (ISE). A special case of such an ion-selective electrode is the known pH glass electrode, which has a chamber which is closed by a pH-sensitive glass membrane and includes an internal electrolyte contained therein and a discharge element immersed therein.
Amperometric sensor elements, e.g., amperometric disinfection sensors, may, for example, have an—in particular, potentiostatic—control circuit which is designed to preset a nominal voltage between a working electrode and a reference electrode and to detect the current flowing between the working electrode and the counter electrode in the process. One example of an amperometric sensor element is described in DE 10 2008 039 465 A1, for example.
Other examples of electrochemical sensor elements are such as are based upon electrolyte isolator semiconductor layer stacks (for short: EIS). These layer systems may, for example, be operated capacitively or as ion-selective field-effect transistors (ISFET). DE 198 57 953 A1 describes such a sensor element designed to measure the ion concentration or the pH value of a measuring medium using an ISFET.
Within the scope of this application, the term, “electrochemical sensor elements,” furthermore includes conductively- or capacitively-operating conductivity sensors, as well as (spectro)photometrically-operating sensors, such as turbidity sensors.
The sensor elements are in this case in contact with the process via the process connection and thus typically, at least partially and at least intermittently or, in particular, substantially mostly, come into contact with the measuring medium. In the case where the sensor element is an electrochemical sensor element used in the aforementioned industries, regular removal of the sensor element from the process is necessary.
On the one hand, the removal serves to clean the sensor element at regular intervals—for example, in order to cleanse it of bacteria and other microorganisms. In this respect, autoclaving, in which the sensor element is cleaned at high temperature (approx. 140° C.) and high pressure using water vapor, has proven itself as the sterilization method. Autoclaving is used, in particular, for electrochemical sensor elements—for example, in the pharmaceutical industry, food industry, medical technology, and to her fields.
On the other hand, calibration, verification, and/or adjustment of the sensor element may be necessary at regular intervals. In this case, calibration usually means the determination of a deviation of the first measured value measured by the sensor element from a reference measured value provided by a second sensor element and accepted as correct. The verification also comprises the determination of the deviation and its assessment or evaluation. Lastly, adjustment means the adaptation of the sensor element in such a way that a model used by the sensor element to determine a measured value from a raw value is adapted such that the measured value corresponds to the reference value provided by the second sensor element. The sensor element also has to be removed from the process for calibration, verification, and/or adjustment.
Depending upon the degree to which the electrochemical sensor element is stressed and/or damaged in the process by the contact with the measuring medium and/or the aforementioned regular cleaning, a regular exchange of the sensor element may also be necessary.
In order to process and/or transmit electronic and/or electrical signals generated by the sensor element—for example, to a transmitter unit or a higher-level unit, e.g., a control center—the sensor element is often connected to a connection element.
The connection element comprises a cable attachment and a cable, which in turn is connected to the higher-level unit. An interface that is, for example, designed to be inductive or optical is respectively located on the sensor element and on the connection element. Via these interfaces, the sensor element is supplied with energy, and/or communication between the sensor element and the connection element is ensured; this is described, for example, in EP 1 625 643.
In this respect, reference is also made, in particular, to the products with the name, “Memosens,” by the applicant. Other generic designs are, for example, “Memosens” by the company Knick, “ISM” by Mettler-Toledo, the “ARC” system by Hamilton, and “SMARTSENS” by Krohne.
The great advantage of the known “Memosens” plug connection is that the above-described regular removal of the sensor element from the process is easily possible. The sensor element can be removed from the process easily and can, where applicable, be brought into the laboratory for calibration and/or adjustment (for example, by means of a so-called “Memobase Plus” system). When a first sensor element is removed, for example, it can, moreover, be replaced directly at the measuring site close to the process by a second sensor element. As a result, the maintenance duration or idle times of the process system and, ultimately, also the costs are drastically reduced. Another advantage is that the electronic components of the sensor element and of the connection element are protected as a result of their—where applicable—liquid-tight design when the plug connection is disconnected. This is important in order to prevent, for example, moisture ingress during a hot steam jet cleaning used for hygienic reasons in the industries mentioned at the beginning.
A disadvantage of the connection by means of the connection element with cable attachment and cable is that a connected transmitter unit must be placed at a distance from the sensor element itself. An arrangement of the transmitter unit close to the process or close to the sensor element is, however, often desired, even if only to be able to calculate and display the process variable, which can be determined by the sensor element in combination with the transmitter unit, close to the process. Within the scope of the application, a “transmitter unit” refers to a unit which comprises electronic components and by means of which at least the process variable of the sensor element can be determined completely, and with which a standardized transmission of the process variable to a higher-level unit is possible. For this purpose, the transmitter unit has, for example, a microprocessor and/or a storage unit.
Such a standardized transmission takes place using a standardized wired or wireless communications network. In the simplest case, this network is formed as a measurement transmission path according to the 4-20 mA standard. A wired communications network can, for example, furthermore be a wired fieldbus of automation technology, such as Foundation Fieldbus, Profibus PA, Profibus DP, HART, CANBus, etc. It can, however, also be a modern industrial communications network, such as an “Industrial Ethernet” fieldbus—in particular, Profinet, HART-IP, or Ethernet/IP, or a communications network known from the communications sector, such as Ethernet according to the TCP/IP protocol. In the case of a wireless communications network, it can, for example, be a Bluetooth, ZigBee, WLAN, GSM, LTE, UMTS communications network, or even a wireless version of a fieldbus—in particular, of a standard based upon 802.15.4, such as WirelessHART.