SENSOR AND SENSOR ARRANGEMENT

Abstract

Disclosed is a sensor comprising a sensor element that detects a measurand, the sensor element being in electrical contact with a sensor circuit that processes values derived from data from a secondary coil and/or from the measurand. The sensor circuit is in electrical contact with an ex-circuit. The sensor circuit is supplied a maximum input voltage and a maximum input current. The ex-circuit includes the secondary coil that receives an electrical signal from a primary coil. The electrical signal includes the data that are modulated onto the electrical signal. The sensor also includes a voltage limit that limits the voltage of the electrical signal to the maximum input voltage of the sensor circuit and a current limit that limits the current of the electrical signal to the maximum input current of the sensor circuit. Also disclosed are a sensor arrangement and a use of a sensor.

Claims

1-12. (canceled)

13. A sensor, comprising: a sensor element that detects a measurand, wherein the sensor element is in electrical contact with a sensor circuit, the sensor circuit that processes values derived from data from a secondary coil and/or from the measurand, wherein the sensor circuit is in electrical contact with an ex-circuit, wherein the sensor circuit is supplied a maximum input voltage and a maximum input current, and the ex-circuit including: the secondary coil that receives an electrical signal from a primary coil associated with the secondary coil, wherein the electrical signal includes the data that are modulated onto the electrical signal, a voltage limit that limits a voltage of the electrical signal to the maximum input voltage of the sensor circuit, and a current limit that limits a current of the electrical signal to the maximum input current of the sensor circuit.

14. The sensor according to claim 13, wherein an intrinsic safety of the sensor circuit is designed by means of the maximum input voltage and the maximum input current.

15. The sensor according to claim 13, wherein the voltage limit includes at least one diode.

16. The sensor according to claim 13, wherein the voltage limit is configured by means of a thyristor crowbar circuit.

17. The sensor according to claim 13, wherein the current limit is configured as an internal resistance of the secondary coil.

18. The sensor according to claim 13, wherein the current limit is configured as a resistor before and/or after the voltage limit.

19. The sensor according to claim 13, wherein the sensor circuit comprises a second ex-circuit on a side facing away from the ex-circuit, wherein the second ex-circuit is configured as an output limit.

20. The sensor according to claim 13, wherein the sensor is embodied to be used in an area with explosion hazards, including zone 0, 1, 20, or 21 or class I division 1 or class II division 1.

21. A sensor arrangement, comprising: a sensor, including: a sensor element that detects a measurand, wherein the sensor element is in electrical contact with a sensor circuit, the sensor circuit that processes values derived from data from a secondary coil and/or from the measurand, wherein the sensor circuit is in electrical contact with an ex-circuit, wherein the sensor circuit is supplied a maximum input voltage and a maximum input current, and the ex-circuit including: the secondary coil that receives an electrical signal from a primary coil associated with the secondary coil, wherein the electrical signal includes the data that are modulated onto the electrical signal, a voltage limit that limits a voltage of the electrical signal to the maximum input voltage of the sensor circuit, and a current limit that limits a current of the electrical signal to the maximum input current of the sensor circuit; and a cable of a first type, including a cable circuit including the primary coil, wherein the primary coil transmits the electrical signal at a maximum power to the secondary coil.

22. The sensor arrangement according to claim 21, wherein the sensor arrangement is configured for use in an area with explosion hazards.

23. The sensor arrangement according to claim 21, wherein the sensor arrangement comprises a cable of a second type instead of the cable of the first type, and the sensor arrangement is configured for use in an area with explosion hazards.

24. A method for operating a sensor in an area with explosion hazards, the method comprising: transmitting an electrical signal, wherein the electrical signal is transmitted at a maximum power to a secondary coil of the sensor; limiting a voltage of the electrical signal to a maximum value, wherein the limiting takes place in the sensor; and limiting a current of the electrical signal to a maximum value, wherein the limiting takes place in the sensor.

Description

[0026] This is explained in more detail with reference to the following figures.

[0027] FIG. 1 shows a schematic overview of the claimed sensor arrangement.

[0028] FIG. 2 shows a schematic overview of the claimed sensor.

[0029] In the figures, the same features are identified by the same reference signs.

[0030] As mentioned, the object is to decouple the secondary side from the primary side from an ex-technical point of view. This is achieved by limiting the input parameters of the secondary side on the secondary side itself. Under this condition, it is possible to “place” an ex-interface directly into the inductive coupling.

[0031] In principle, a device can be certified as an “intrinsically safe device” in two different ways: as a system or via parameters. In a certification via the system per se, the inspection authority (certification authority) specifies each component and then assesses the entire system. Deviation of a component from the corresponding standard results in termination of the approval. In contrast, a parametric approval is one in which the inspection authority individually assesses each device per se and assigns it a set of safety or so-called entity parameters.

[0032] For the inductive coupling by means of a primary coil L1 and a secondary coil L2, the output power Po at the primary coil L1 or the input power Pi at the secondary coil L2 can be used as an entity parameter, because the power transmission as such is measurable and constant. The following applies: Pi≥Po. This means that the cable electronics (primary side) have a maximum output power Po and the sensor electronics have a corresponding input power Pi. The output power Po of the cable electronics is independent of the secondary side and is also determined or calculated without this. The input power Pi of the sensor electronics is oriented towards the output power Po and is at least the same as or greater than the output power Po. The maximum output power Po is thus less than the input power Pi.

[0033] FIG. 1 shows the schematic overview of the sensor arrangement with the cable side K, which corresponds to the primary side P, and the sensor side S, which corresponds to the secondary side. Through an ex-circuit 3 on the secondary side, the effect that the secondary side S, i.e. the sensor, can be used in the ex-area is only achieved by secondary-side measures.

[0034] The exclusively sensor-side consideration of all functional and Ex-technical parameters allows, for example, the number of windings or the type of secondary coil to be adapted to the sensor-specific conditions. Thus, the number of windings can be reduced to reduce, for example, the power dissipation while stabilizing the secondary DC voltage. It is also conceivable to use a secondary coil with a center tap, in order to potentially optimize the energy decrease for the positive and negative half-wave or decouple it from the communication. These measures result in an optimization of the actual sensor functionality and thus enable a more accurate or precise measurement of the primary measurand (pH, conductivity, etc.) and/or the secondary measurand (temperature, etc.). This is achieved because more scans for digitizing the measurand are possible, higher computing power of the microcontroller used (e.g. through higher processor clocking) is possible, more accurate and/or lower-noise op-amps can be used, a higher measuring current can be fed and higher circuitry complexity can be driven.

[0035] From the perspective of the sensor (seen in the direction of the cable), the primary side is unknown. This means that both functional parameters (e.g. winding ratio) and ex-technical parameters have to be treated or limited on the sensor electronics. The following limiting circuit parts must be present in order for further calculation of the intrinsic safety of the sensor to be able to take place: Voltage limit and current limit.

[0036] FIG. 2 shows schematically how and where the ex limiting circuits are arranged. The secondary coil L 2 receives an electrical signal from the primary side P. The limiting circuit 3 limit this electrical signal to fixed values so that defined maximum values for voltage U_max and current I_max are supplied to the sensor circuit 4. These maximum values are further required to calculate the intrinsic safety of the sensor circuit 4.

[0037] The sensor circuit 4 comprises the functional part of the sensor 2. For this purpose, the circuit comprises approximately one or more microcontrollers and one or more storage devices. The sensor circuit 4 also comprises a modulator and/or a demodulator. With this, data are impressed, for instance modulated, onto the electrical signal, or data from the electrical signal are demodulated.

[0038] The sensor circuit 4 comprises a second ex-circuit 6, which limits the sensor circuit 4 on the output side. The ex-circuit 6 comprises at least one current limit and/or a voltage limit. The second ex-circuit 6 as an output limit ensures that the normative intrinsic safety requirements of the sensor circuit in the direction of the sensor element are complied with. Furthermore, the output limiting circuit ensures that the normative intrinsic safety requirements of the sensor circuit are complied with if the sensor circuit can be damaged by errors in the sensor element. Embodiments of the ex-circuit 6 comprise a resistor, one or three Z diodes or a thyristor crowbar circuit.

[0039] The sensor element 5 is configured to detect a measurand. This may be, for example, the pH or the conductivity. Further characteristic values are, for instance, the redox potential, the absorption of electromagnetic waves in the medium, for example with wavelengths in the UV, IR and/or visible range, oxygen concentration, turbidity, concentration of non-metallic materials, among other things. Other measured values, such as the temperature, that are necessary for the correct determination of this value are also intended to fall under the term “sensor element 5.”

[0040] The current limit I_limit may be an independent component, e.g. a resistor R1 or R2 or R1 and R2, arranged “before” or “after” the voltage limit. The resistor R1, R2 is thus connected in series with the secondary coil L2. If only one resistor R1 or R2 is used, it can be arranged before or after the node for the voltage limit U_Iimit. Alternatively or additionally, the internal resistance of the secondary coil L2 can also be used for this purpose if the coil is a non-susceptible component according to the ex-standard. The maximum current I_max results from the calculation:

[00001]$I_{\max }=\frac{\mathrm{Pi}}{R}$

[0041] Here, the variable “R” in the formula is the sum of all resistances, for instance R1+R2+R_(internal resistance of the coil L2).

[0042] In the simplest case, the voltage limit U_limit can be implemented with a Z diode circuit D. Three parallel-connected diodes are preferably used. Here, the maximum voltage results from the Z voltage plus tolerances (e.g. component, temperature). The Z diodes are designed such that the reverse voltage, i.e. the voltage at the voltage limit, is higher than the input voltage of the sensor circuit 4. This is advantageous because, above a certain reverse voltage, the breakdown voltage, the current through the diode undesirably increases by many orders of magnitude and causes power dissipation.

[0043] However, other circuit designs are also possible, such as, for example, a crowbar circuit (when an overvoltage is detected, a transverse path is immediately opened and the voltage is drawn toward 0 V).

[0044] This results in an independent ex-design on the sensor side as long as the output power is below the input power.

[0045] Changes to standard parameters, such as, for example, the winding ratio of the coils L1, L2, are thus possible even under ex-conditions.

[0046] Each individual sensor type can be technically optimized for its task without regard to existing parameter sets.

[0047] Furthermore, all sensors which are permitted in the ex-area can be connected to a primary side. In this case, it does not matter who the manufacturer of the sensor is.

LIST OF REFERENCE SIGNS

[0048] 1 Sensor arrangement [0049] 2 Sensor [0050] 3 Ex-circuit [0051] 4 Sensor circuit [0052] 5 Sensor element [0053] 6 Second ex-circuit [0054] D Diode [0055] l_limit Current limit [0056] I_max Maximum input current [0057] L1 Primary coil [0058] L2 Secondary coil [0059] K Cable side [0060] Pi Power at L2 [0061] Po Line to L1 [0062] R1 Resistor [0063] R2 Resistor [0064] S Sensor side [0065] U_Iimit Voltage limit [0066] U_max Maximum input voltage