Circuit arrangement and input module having such a circuit arrangement

Abstract

The invention relates to a circuit arrangement (21), in particular a fail-safe circuit arrangement, for detecting a signal state of at least one sensor (S), the circuit arrangement comprising, for the sensor (S) or for each of the sensors: an output (3) for providing a supply voltage (V) for the sensor (S); an input (4) for detecting a sensor current (IS) generated by the sensor (S) on the basis of the supply voltage (V); and an evaluation device (30) which is designed to determine the sensor current (IS) and to derive therefrom the signal state of the particular sensor (S). According to the invention, the evaluation device (30) is also designed to determine, for the sensor (S) or for each of the sensors, a value of a supply current (IV) flowing to the sensor (S) via the output (3) and a value of the sensor current (IS) flowing from the sensor (S) via the input (4). The evaluation device is also designed to compare the two values and to initiate an error response if the values differ. In this way, with a high level of fail safety, the time of response to external short circuits can be reduced.

Description

[0001] 202415835 Foreign version

[0002] 1

[0003] Description

[0004] Circuit arrangement and input module with such a circuit arrangement

[0005] The invention relates to a circuit arrangement, in particular a fail-safe arrangement, for detecting signals from at least one sensor according to claim 1, and to an input module, in particular a fail-safe arrangement, with such a circuit arrangement according to claim 13.

[0006] In automation environments, automation devices or programmable logic controllers (PLCs) are frequently used, which can access connected peripheral units or distributed I / O systems for reading and / or writing. These peripheral units or distributed I / O systems typically comprise several peripheral modules.

[0007] Such peripheral assemblies can, for example, be designed as digital input modules (sometimes also referred to as peripheral modules) for capturing signals from at least one sensor.

[0008] In potentially explosive atmospheres, sensors (or transmitters) conforming to IEC 60947-5-6 (NAMUR) (hereinafter referred to as "NAMUR sensors") are predominantly used. NAMUR sensors generate signals by changing their internal resistance, which, when the sensor is supplied with a constant DC voltage, can be detected as different currents. NAMUR sensors typically represent binary information.

[0009] For example, a digital input module applies a supply voltage of 8.2 V to a connected NAMUR sensor, whereby different signal states "0", "1", "open circuit", or "short circuit" are represented by currents induced by the sensor. The signal states "0" and "1" are sometimes also referred to as "process values". A sensor current of less than 0.35 mA represents an open circuit between the NAMUR sensor and the digital input module, a sensor current of 0.35 mA to 1.2 mA a signal state "0", a sensor current of 2.1 mA to 7 mA a signal state "1", and a sensor current greater than 7 mA a short-circuited NAMUR sensor. The sensor current flows, for example, through a low-resistance measuring resistor (shunt) of the digital input module and causes a voltage drop across this measuring resistor (e.g., 1 kOhm) proportional to the impressed sensor current, which internally determines the signal state of the NAMUR- 202415835 foreign version

[0010] 2

[0011] The sensor is represented or mapped. For example, if the NAMUR sensor of the digital input module applies a current of 2.4 mA, a voltage of 2.4 V drops across the measuring resistor, and this voltage drop is interpreted by the digital input module as a signal state "1".

[0012] The digital input module comprises a circuit arrangement for detecting a signal state from at least one sensor, wherein the circuit arrangement for the sensor or each of the sensors is

[0013] - an output to provide a supply voltage for the sensor and

[0014] - includes an input for detecting a sensor current generated by the sensor due to the supply voltage.

[0015] Furthermore, the circuit arrangement includes an evaluation unit designed to determine the sensor current and derive the signal state of the respective sensor from it. The evaluation unit can, for example, comprise one or more microcontrollers.

[0016] The input for detecting a sensor current generated by the sensor due to the supply voltage is often also referred to as a "channel," and the sensor current as the "channel current." Commercially available digital input modules or associated circuit arrangements have inputs for connecting, for example, 16 sensors; that is, they have 16 channels.

[0017] Such a circuit arrangement is known, for example, from EP 0 920 603 B1. A digital input unit with such a circuit arrangement is known, for example, from EP 3 200 033 B1.

[0018] Fail-safe digital input modules use redundant current measurement to prevent internal errors. This is achieved, for example, through a redundant architecture consisting of two evaluation units, each comprising a microcontroller. Within the module, the sensor current is symmetrically divided using two voltage dividers. One microcontroller measures the current through the first of the two voltage dividers, and the second microcontroller measures the current through the second of the two voltage dividers; that is, each microcontroller measures half of the sensor current. The two results are then compared. If both current values ​​are within a permissible limit, the corresponding sensor signal state is transmitted to the automation device or the programmable logic controller (PLC). In the event of an implausible deviation, the module detects an error and outputs a substitute value for the signal state.The fault in the module then leads to a safe shutdown of the automation device or the 202415835 foreign version.

[0019] 3. Programmable logic controller (PLC) controlled device within a defined fault response time. Such an internal fault can be detected on the order of < 100ms.

[0020] Unlike faults within the module, external faults, according to current technology, can only be detected by testing after a significantly longer period. An external fault in the form of a short circuit can lead to a dangerous signal state (or process value). This is particularly true for a multi-channel digital input module in the case of a cross-circuit between two channels. For example, the sum of the currents from one sensor (logical 0) and one sensor (logical 1) can result in a logical 1 on both channels. This extremely critical case can be detected by the module using a so-called SVS test (SVS = Sensor Voltage Supply). During the SVS test, the supply to a sensor or channel is switched off at the output, and it is checked whether current flows into the input. However, electronic sensors require a start-up phase when the sensor is powered again after the SVS test.For this purpose, a user of a digital input module can parameterize a ramp-up time (e.g., up to 2 seconds). With a multi-channel module, the supply voltage must be successively switched off for each individual channel for the SVS test, the test performed, and then the ramp-up time waited for. The reaction time to external short circuits is then the sum of the ramp-up times of all sensors. For a 16-channel module, the reaction time (without considering other tests) is therefore at least 16 times the ramp-up time (e.g., at least 32 seconds). The reaction time is thus two orders of magnitude longer than for internal faults.

[0021] Document DE 102019 113139 A1 discloses a device for current control of an actuator, comprising a current measuring device for measuring the current flowing into and out of the actuator. The device further comprises an evaluation unit configured to compare the two currents and output a fault signal if the comparison indicates a fault current. This allows for improved control of the actuator in the event of defects upstream or downstream of the actuator (e.g., current flow to ground or to a different voltage level).

[0022] Document DE 44 34 180 A1 addresses the challenge of ensuring reliable detection of a sensor's output signal even under unfavorable voltage and component tolerances. It also aims to detect short circuits between the sensor leads and ground, the power supply, and between the sensor leads themselves. A circuit arrangement for evaluating the sensor's output signal is disclosed for this purpose (see German patent application DE 202415835, foreign version).

[0023] 4. The sensor is connected on one side to a supply voltage and on the other side to ground via a current mirror circuit. The relatively high sensor current is transformed by the current mirror into a smaller current that can be evaluated with low power consumption. This current is drawn from a stabilized voltage source via an ohmic resistor to generate a voltage signal that can be evaluated using a flip-flop circuit and represents the waveform of the sensor signal. By varying or adjusting a switching threshold of the flip-flop circuit, reliable detection and evaluation of the sensor signal is ensured even with unfavorable tolerances, superposition of leakage currents, or short circuits. If the leakage currents or short circuits exceed a certain limit, or if a sensor fault, open circuit, or similar condition is present, the circuit is deactivated.The faulty condition is detected and signaled using the current mirror current derived from the sensor current and a window comparator.

[0024] Based on this, the object of the present invention is to provide a circuit arrangement characterized by high fault tolerance and a short reaction time to external short circuits.

[0025] This problem is solved by a circuit arrangement, in particular a fail-safe one, according to claim 1. An input module, in particular a fail-safe one, with such a circuit arrangement is the subject of claim 13. Advantageous embodiments are the subject of the dependent claims.

[0026] A circuit arrangement according to the invention, in particular a fail-safe circuit arrangement, for detecting a signal state from at least one sensor, comprises for the sensor or each of the sensors, respectively

[0027] - an output to provide a supply voltage for the sensor and

[0028] - an input for detecting a sensor current generated by the sensor due to the supply voltage.

[0029] Furthermore, the circuit arrangement includes an evaluation device designed to determine the sensor current and derive the signal state of the respective sensor from it.

[0030] According to the invention, the evaluation device is designed to provide a reading for the sensor or each of the sensors.

[0031] - to determine the value of a supply current flowing into the sensor via the output,

[0032] - to determine a value of the sensor current flowing from the sensor via the input, 202415835 Foreign version

[0033] 5

[0034] - to compare the two values ​​and trigger an error response if the values ​​differ.

[0035] The inventive idea is to modify the concept of redundant measurement so that both the current from the sensor supply and the sensor current (or "channel current") are measured simultaneously. An external short circuit, especially a cross-circuit between two channels, can be detected immediately, as the supply current will then deviate from the sensor current (or "channel current"). Since two current values ​​are still being compared, the requirements for fault tolerance in determining the signal state are met.

[0036] An SVS test involving a sensor power interruption is no longer necessary. This also eliminates the start-up phase or ramp-up time required in the previous SVS test when the sensor is re-energized. As a result, the response time can be reduced to the millisecond range. For example, with 16 channels, the response time is reduced from 32 seconds to 50 ms.

[0037] The invention therefore offers enormous advantages in terms of error response time.

[0038] The determination of the value of the supply current and / or the sensor current can also be done indirectly by determining a dependent quantity such as a voltage drop across a measuring resistor (measuring shunt) through which the respective current flows.

[0039] According to an advantageous embodiment, the evaluation device is configured to generate an alarm signal as an error response and / or to passivate the input (i.e., for example, a predefined substitute value for the signal state of the sensor is output).

[0040] According to a further advantageous embodiment, the evaluation device is designed to trigger the error response if the two values ​​differ from each other by more than a predefined threshold.

[0041] According to a further advantageous embodiment, the evaluation unit is configured to output the signal state of the respective sensor when the two values ​​are within a permissible limit, in particular when the two values ​​differ from each other by less than a predefined threshold (preferably less than the aforementioned predefined threshold for triggering the fault response). 202415835 Foreign version

[0042] 6

[0043] To increase fault tolerance, the evaluation unit can

[0044] - comprising a first evaluation unit for determining the value of the sensor supply current or supply currents of the sensors and a second evaluation unit for determining the value of the sensor current or sensor currents of the sensors, wherein the two evaluation units determine the values ​​independently of each other.

[0045] The first evaluation unit and the second evaluation unit can each include at least one microcontroller.

[0046] According to a further advantageous embodiment, the evaluation device for determining the value of the supply current comprises a current mirror that detects the supply current on its input side and generates a mirror current on its output side that has the value of the supply current. A current mirror is an electronic circuit that serves to derive and copy a current from a reference current. A simple current mirror typically consists of two transistors. The reference current flows through the first transistor, thereby generating a specific voltage. This voltage is then transferred to the second transistor, causing an identical current to flow through it. Higher accuracy is possible with current mirrors based on operational amplifiers. Using the current mirror, it is possible to bring the reference point for measuring the supply current to a desired potential (in particular, potential = 0 or ground).This is advantageous, for example, if the supply voltage is higher than the maximum permissible voltage at the input of a microcontroller for determining the supply current (e.g., supply voltage = 8.2 V, maximum input voltage at the microcontroller = 2.5 V).

[0047] According to a circuit design that is particularly simple in terms of circuit technology, the evaluation device for determining the value of the supply current comprises a first electrical measuring resistor through which the supply current or the mirror current flows.

[0048] According to a further circuit design that is particularly simple in terms of circuit technology, the evaluation device for determining the value of the sensor current comprises a second electrical measuring resistor through which the sensor current flows.

[0049] According to a particularly advantageous embodiment, at least one sensor is designed as a sensor according to IEC 60947-5-6 (NAMUR), i.e., it meets the requirements of this standard. 202415835 Foreign version

[0050] 7

[0051] An input module according to the invention, in particular a fail-safe input module, for acquiring a signal state from at least one sensor, comprises a circuit arrangement according to one of the preceding claims. Furthermore, the module can comprise a housing and a terminal block for each of the outputs and inputs. For communication with a higher-level automation device, it can further comprise a communication interface, in particular a bus interface.

[0052] The invention and further advantageous embodiments of the invention according to features of the dependent claims are explained in more detail below with reference to exemplary embodiments shown in the figures. These show:

[0053] FIG 1: A fail-safe circuit arrangement for detecting a signal state from a sensor according to the prior art,

[0054] FIG 2: A fail-safe circuit arrangement for detecting a signal state from one sensor according to the prior art in the event of a short circuit to another sensor,

[0055] FIG 3: A fail-safe circuit arrangement according to the invention for detecting a signal state from a sensor,

[0056] FIG 4: a fail-safe digital input module according to the invention.

[0057] A fail-safe circuit arrangement 1, shown in simplified and schematic form in FIG. 1, according to the prior art, for detecting a signal state from a NAMUR sensor S, comprises an output 3 for providing a supply voltage V for the sensor, an input 4 ("channel") for detecting a sensor current Is generated by the sensor S due to the supply voltage V, and an evaluation unit 10 configured to determine the sensor current Is and derive the signal state of the sensor S from it. The circuit arrangement 1 further includes a DC voltage supply 9 for providing the supply voltage V, which is connected to the output 3. The circuit arrangement 1 is used, for example, in a digital input module. For better illustration, FIG. 1 shows a line 15, with a section to the left of line 15.Circuit arrangement 1 is located up to line 15, and sensor S is located in an area to the right of line 15. 202415835 Foreign version.

[0058] 8

[0059] For example, sensor S indicates whether a reference object is nearby or not.

[0060] The circuit arrangement 1 comprises two parallel-connected voltage dividers 7, 8, which are electrically connected to the input 4 and divide the sensor current Is symmetrically into two partial currents ls a and divide Isb. The voltage dividers 7, 8 each comprise two resistors Ri and R2 connected in series.

[0061] The evaluation unit 10 comprises one evaluation unit 11 and one 12 for each of the voltage dividers 7, 8, each preferably comprising at least one microcontroller. The evaluation unit 11 detects a value of the partial current ls aThe evaluation unit 11 measures the voltage drop across resistor R2 of voltage divider 7. Similarly, the evaluation unit 12 measures the voltage drop across resistor R2 of voltage divider 8 and transmits this value to the evaluation unit 12 via a signal line 13. The evaluation unit 11 compares the two values. If both current values ​​are within a permissible limit, the evaluation unit 11 transmits the corresponding signal state (or process value) of sensor S to a higher-level automation device or a programmable logic controller (PLC) via a communication interface 14 (e.g., a bus interface). In the event of an implausible deviation, the evaluation unit 11 detects an error and outputs a substitute value for the signal state via the communication interface 14.

[0062] An external fault in the form of a short circuit can lead to a dangerous signal state (or process value). This is particularly true for a multi-channel circuit arrangement in the case of a cross-circuit between two channels, as indicated in FIG. 2. S' denotes a second sensor connected to a second output 3' of the circuit arrangement 1, which provides the supply voltage V for sensor S'. Sensor S' is also connected to a second input 4' of the circuit arrangement 1 to detect a sensor current generated by sensor S' due to the supply voltage V. A line 25 symbolizes a cross-circuit between sensors S and S'. If the sensor current Is of sensor S represents a logic 0 and the sensor current ls' of sensor S' represents a logic 1, the sum of the currents can result in a logic 1 on both inputs 4 and 4', or both channels.

[0063] This extremely critical case can be detected according to the state of the art using a so-called SVS test (SVS = Sensor Voltage Supply). For this purpose, a test switch 16 or 16' is connected between the DC voltage supply 9 and each of the outputs 3, 3'. 202415835 Foreign version

[0064] Switch 9, which is closed in normal operating conditions, is activated. Evaluation unit 11 then successively controls switches 16 and 16' at predefined time intervals via control signals X and X', causing them to open for a predefined test period and thus switching off the power supply to the respective sensor S and S'. Evaluation units 11 and 12 then check whether a signal current flows through input 4 and 4', respectively. However, since electronic sensors require a warm-up time after switches 16 and 16' close and the power supply is restored, the test takes a relatively long time (e.g., 2 seconds per sensor).

[0065] A fail-safe circuit arrangement 21 according to the invention, shown in simplified and schematic form in FIG. 3, comprises an evaluation unit 30 configured to determine the sensor current Is and to derive the signal state of the sensor S from it. It is configured to determine a value of a supply current l for the sensor S. vThe evaluation unit 30 is configured to determine the signal state of sensor S, which flows via output 3 into sensor S, and a value of the sensor current Is, which flows from sensor S via input 4. The two current values ​​are then compared, and an error response is triggered if they differ (e.g., if the two current values ​​differ by more than a predefined threshold). The evaluation unit 30 is preferably further configured to output the signal state of sensor S when the two values ​​are within a permissible limit, particularly when the two values ​​differ by less than a predefined threshold.

[0066] The evaluation unit 30 comprises a first evaluation unit 31 for determining the value of the supply current lv and a second evaluation unit 32 for determining the value of the sensor current Is. The first evaluation unit 31 is additionally configured to compare the two current values ​​and to trigger the fault response. The first evaluation unit 31 is preferably also configured to output the signal status. Both evaluation units 31 and 32 determine the current values ​​independently of each other and are each implemented as a microcontroller.

[0067] To determine the value of the supply current lv, the circuit arrangement 21 comprises a measuring resistor R3 connected between a DC voltage supply 39 and the output 3, a current mirror 35, and a measuring resistor R4. The current mirror 35 detects the supply current lv at its input based on the voltage drop across the measuring resistor R3 and generates a mirror current lv at its output that has the value of the supply current lv. The measuring resistor R4 is connected between the output of the current mirror 35.

[0068] 10 and a reference potential (ground) M of the circuit arrangement 21. The first evaluation unit 31 then determines the value of the mirror current ly and thus the value of the supply current l based on the voltage drop across the measuring resistor R4. v .

[0069] To determine the value of the sensor current Is, the circuit arrangement 21 includes a measuring resistor Rs connected between the input 4 and the reference potential (ground) M, where R4 and R5 each have the same electrical resistance value. The second evaluation unit 32 determines the value of the sensor current Is based on the voltage drop across the measuring resistor Rs and communicates this value to the evaluation unit 31 via a signal line 43.

[0070] The redundant measurement concept explained with reference to Figures 1 and 2 is thus modified such that both the current lv from the sensor supply and the sensor current (or channel current) Is are measured simultaneously. An external short circuit, in particular a cross-circuit between two channels, can be detected immediately, since the value of the supply current lv then deviates from the value of the sensor current (or channel current) Is. Since two current values ​​are still being compared, the requirements for fault tolerance in determining the signal state are met.

[0071] An SVS test involving a channel power interruption is no longer necessary. This also eliminates the start-up phase or ramp-up time required in the previous SVS test when the sensor is re-energized. As a result, the response time to short circuits can be reduced to the millisecond range. For example, with 16 channels, the response time is reduced from 32 seconds to 50 ms.

[0072] The minimal additional effort required for the new architecture thus offers enormous advantages in terms of fault response time, while redundant current measurement ensures a high level of fault safety.

[0073] The first evaluation unit 31 can, for example, generate an alarm signal as a fault response and output it to a higher-level automation device or a programmable logic controller (PLC) via a communication interface 44 (e.g., a bus interface). The first evaluation unit 31 can also, or alternatively, passivate input 4 (i.e., output a predefined substitute value for the signal state of sensor S via the communication interface 44). 202415835 Foreign version

[0074] 11

[0075] A fail-safe digital input module 50, shown in FIG. 4, is used to detect the signal state of n sensors S1 to Sn (e.g., n = 16). It comprises, for each of the sensors S1 to Sn, an output 3 to provide a supply voltage V for the sensor and an input 4 to detect a sensor current generated by the sensor due to the supply voltage V. The input module 50 has a housing 51 with a terminal block for each of the outputs 3 and inputs 4.

[0076] An evaluation device 30 comprises a first evaluation unit 31, which is designed to measure the values ​​of the supply currents l Vi to determine up to Ivn, and a second evaluation unit 32, which is designed to determine the values ​​of the sensor currents Isi to ls n to determine. The first evaluation unit 31 is additionally designed to determine the two current values ​​l vThe current values ​​(Is) of each sensor are compared, and an error response is triggered if the values ​​differ (as already explained in connection with FIG. 3). Both evaluation units 31 and 32 determine the current values ​​(lv and Is) independently of each other and are each implemented as a microcontroller.

[0077] To determine the values ​​of the supply flows l Vi to l Vn The digital input module 50 comprises for each of the sensors S1 - Sn a measuring resistor R3 connected between the voltage supply V and the output 3, a current mirror 35 and a measuring resistor R4 as already explained in connection with FIG 3.

[0078] To determine the values ​​of the sensor currents Isi to Isn, the digital input module 50 includes a measuring resistor Rs for each of the sensors S1 - Sn, connected between output 4 and the reference potential (ground) M, where R4 and R5 have the same electrical resistance value. The second evaluation unit 32 then determines the value of the respective sensor current based on the voltage drop across the measuring resistor Rs and communicates this value to the evaluation unit 31 via a signal line 43.

[0079] The digital input module 50 also includes galvanic isolation 52 and a bus connection 53 with an interface 54 for a bus (e.g., a backplane bus of a peripheral unit or distributed I / O). The sensor states of sensors S1–Sn determined by the evaluation unit 31, or alarm signals generated, are output via the galvanic isolation 52 and the bus connection 53, e.g., to a higher-level automation device or a programmable logic controller (PLC). 202415835 Foreign version

[0080] 12

[0081] The supply voltage V is provided via input 56 of the digital input module 50, and a connection to the reference potential (ground) M is provided via input 55. The invention has been explained in the exemplary embodiments using NAMUR sensors. However, this is not limiting. It can also be used for other sensors, such as classic 2-wire sensors.

Claims

202415835 Foreign version 13 Patent claims 1. Circuit arrangement (21), in particular a fail-safe circuit arrangement, for detecting a signal state of at least one sensor (S), comprising for the sensor (S) or each of the sensors - an output (3) to provide a supply voltage (V) for the sensor (S), - an input (4) for detecting a sensor current (Is) generated by the sensor (S) due to the supply voltage (V), and an evaluation device (30) configured to determine the sensor current (Is) and to derive the signal state of the respective sensor (S) from it, characterized in that the evaluation device (30) is further configured to determine for the sensor (S) or each of the sensors - a value of a supply current (lv) that flows into the sensor (S) via the output (3), - to determine a value of the sensor current (Is) flowing from the sensor (S) via the input (4), - to compare the two values ​​and trigger an error response if the values ​​differ.

2. Circuit arrangement (21) according to claim 1, wherein the evaluation device (30) is configured to generate an alarm signal as a fault reaction.

3. Circuit arrangement (21) according to claim 1 or 2, wherein the evaluation device (30) is configured to passivate the input (4) as an error response, 4. Circuit arrangement (21) according to one of the preceding claims, wherein the evaluation device (30) is configured to output a predefined substitute value for the signal state of the sensor as an error response.

5. Circuit arrangement (21) according to one of the preceding claims, wherein the evaluation device (30) is configured to trigger the error response when the two values ​​differ from each other by more than a predefined threshold.

6. Circuit arrangement (21) according to one of the preceding claims, wherein the evaluation device (30) is configured to output the signal state of the respective sensor (S) when the two values ​​are within a permissible limit, in particular when the two values ​​differ from each other by less than a predefined threshold.

7. Circuit arrangement (21) according to one of the preceding claims, wherein the evaluation device (30) is designed to increase fault tolerance. 202415835 Foreign version 14 - a first evaluation unit (31) for determining the value of the supply current (lv) of the sensor (S) or the supply currents of the sensors and - a second evaluation unit (32) for determining the value of the sensor current (Is) of the sensor (S) or the sensor currents of the sensors, wherein the two evaluation units (31 , 32) each determine the values ​​independently of each other.

8. Circuit arrangement (21) according to one of the preceding claims, wherein the first evaluation unit (31) and the second evaluation unit (32) each comprise at least one microcontroller.

9. Circuit arrangement (21) according to one of the preceding claims, wherein the evaluation device (30) for determining the value of the supply current (lv) comprises a current mirror (35) which detects the supply current (lv) on the input side and generates a mirror current (lv) on the output side which has the value of the supply current (lv).

10. Circuit arrangement (21) according to one of the preceding claims, wherein the evaluation device (30) for determining the value of the supply current (lv) comprises a first electrical measuring resistor (R4) through which the supply current (lv) or the mirror current (lv) flows.

11. Circuit arrangement (21) according to one of the preceding claims, wherein the evaluation device for determining the value of the sensor current (Is) comprises a second electrical measuring resistor (R5) through which the sensor current (Is) flows.

12. Circuit arrangement (21) according to one of the preceding claims, wherein the at least one sensor (S) is designed as a sensor according to IEC 60947-5-6.

13. Input module (50), in particular a fail-safe input module, for detecting a signal state of at least one sensor (S), comprising a circuit arrangement (21) according to one of the preceding claims.

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