LU100452B1 - Method and System for Wire Interruption Detection for Guarded Sensors - Google Patents

Method and System for Wire Interruption Detection for Guarded Sensors Download PDF

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Publication number
LU100452B1
LU100452B1 LU100452A LU100452A LU100452B1 LU 100452 B1 LU100452 B1 LU 100452B1 LU 100452 A LU100452 A LU 100452A LU 100452 A LU100452 A LU 100452A LU 100452 B1 LU100452 B1 LU 100452B1
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Luxembourg
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guard
wire
detection unit
node
detection
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LU100452A
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German (de)
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Thomas John
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Iee Sa
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Priority to LU100452A priority Critical patent/LU100452B1/en
Priority to PCT/EP2018/075520 priority patent/WO2019057843A1/en
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Publication of LU100452B1 publication Critical patent/LU100452B1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/54—Testing for continuity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/28—Testing of electronic circuits, e.g. by signal tracer
    • G01R31/282—Testing of electronic circuits specially adapted for particular applications not provided for elsewhere
    • G01R31/2829—Testing of circuits in sensor or actuator systems

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Current Or Voltage (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)

Abstract

A detection unit (4) for detecting an interruption in a guard wire (14) or sense wire (8) coupling a guarded sensor (6) to the detection unit (4). The detection unit (4) comprises a sense wire output (10) and a guard wire output (16) configured to be coupled, in use, to a sense wire (8) and a guard wire (14), respectively, and a first EMC filter (20), the first EMC filter including a sense node (30) and a guard node (32), each coupled to signal analysis and evaluation circuitry (34), the first EMC filter (20) having a sense wire output (10) coupled to the sense wire output (10) of the detection unit (4). The detection unit further comprises a guard DC blocking element (28) coupled between a guard wire output (16) of the first EMC filter (20) and the guard wire output (16) of the detection unit (4). A guard voltage source (50) is configured to apply a DC voltage to the guard node (32), and a diagnostics voltage source (46) is configured to supply an AC voltage signal to a first junction (48) between the guard DC blocking element (28) and the guard wire output (16) of the detection unit (4). The signal analysis and evaluation circuitry (34) is configured to indicate that the guard wire (14) or sense wire (8) is interrupted if a current out of the sense node (30), l_Sense_Node, is zero. The detection unit (4) includes a current-to-voltage converter (36) coupled across the sense node (30) and a guard node (32), whereby the signal analysis and evaluation circuitry (34) is configured to indicate that the guard wire (14) or sense wire (8) is interrupted if a voltage output by the current-to-voltage converter (36) is zero. A corresponding detection method is also disclosed.

Description

Method and System for Wire Interruption Detection for Guarded Sensors
Technical field [0001] The present invention generally relates to diagnosing the status of electronic sensors, e.g. for use in automotive applications, and more particularly to a method and system for wire interruption detection for guarded sensors.
Background of the invention [0002] For safety reasons, it is necessary to detect a wire interruption of a guarded sensor. To do this, several methods can be used.
[0003] In one known technique, a passive component is used inside the sensor, between the sense and the guard electrode. A DC voltage is applied to the two sensor cables and the current through the passive component is determined.
[0004] In another known technique, two additional wires shorted to the sense and guard electrode are used to determine the loop connection.
[0005] In another known technique, a guard node is unbalanced to create a voltage difference between sense and guard electrode. Due to the sense-guard impedance, an additional current can be determined.
[0006] However, a difficulty is to determine only the sense-guard impedance without influences from other components (EMC-, filter components, tolerances) or external effects (sense-GND load variation, EMC disturbance). With known diagnostics techniques it is not possible to detect an interruption for all given conditions.
Object of the invention [0007] A problem addressed by the present invention is how to provide an effective method and system for determining whether a sense or guard wire is interrupted or not.
General Description of the Invention [0008] In order to overcome the abovementioned problems, the present invention provides a detection unit for detecting an interruption in a guard wire or sense wire coupling a guarded sensor to the detection unit. The detection unit comprises a sense wire output and a guard wire output configured to be coupled, in use, to a sense wire and a guard wire, respectively, and a first EMC filter, the first EMC filter including a sense node and a guard node, each coupled to signal analysis and evaluation circuitry, the first EMC filter having a sense wire output coupled to the sense wire output of the detection unit. The detection unit further comprises a guard DC blocking element coupled between a guard wire output of the first EMC filter and the guard wire output of the detection unit. The detection unit further comprises a guard voltage source, configured to apply a DC voltage to the guard node. The detection unit further comprises a diagnostics voltage source configured to supply an AC voltage signal to a first junction between the guard DC blocking element and the guard wire output of the detection unit. The signal analysis and evaluation circuitry is configured to indicate that the guard wire or sense wire is interrupted if a current out of the sense node, l_Sense_Node, is zero.
[0009] Preferably, the diagnostics voltage source is coupled to the first junction via a diagnostics DC blocking element. Preferably, a second EMC filter is connected between the diagnostics voltage source and the diagnostics DC blocking element.
[0010] In one embodiment, a current-to-voltage converter is coupled across the sense node and a guard node of the first EMC filter. Preferably, the signal analysis and evaluation circuitry is configured to indicate that the guard wire or sense wire is interrupted if a voltage output by the current-to-voltage converter is zero.
[0011] Preferably, the AC voltage signal has a predefined frequency. Preferably, the signal analysis and evaluation circuitry is configured to operate in a frequency selective manner, whereby the detection unit is insensitive to received currents or voltages at frequencies which are not equal to the predefined frequency.
[0012] In one embodiment, the AC voltage signal is amplitude or frequency modulated.
[0013] In a possible embodiment, a switching element is arranged between the guard DC blocking element and the guard node of the EMC filter. By opening the switching element, any influence of the EMC filter on the diagnostics circuitry may be entirely eliminated which results in an increased robustness of the detection.
[0014] According to another aspect of the invention there is provided a method for detecting an interruption in a guard wire or sense wire coupling a guarded sensor to a detection unit. The method comprises providing a detection unit, the detection unit including a sense wire output and a guard wire output configured to be coupled, in use, to a sense wire and a guard wire, respectively, and a first EMC filter, the first EMC filter including a sense node and a guard node, each coupled to signal analysis and evaluation circuitry, the first EMC filter having a sense wire output coupled to the sense wire output of the detection unit. A guard DC blocking element may be coupled between a guard wire output of the first EMC filter and the guard wire output of the detection unit. The method further comprises applying, using a guard voltage source, a DC voltage to the guard node. The method further comprises supplying, using a diagnostics voltage source, an AC voltage signal to a first junction between the guard DC blocking element and the guard wire output of the detection unit. The method further comprises measuring, using the signal analysis and evaluation circuitry, a current out of the sense node, l_Sense_Node, and indicating, using the signal analysis and evaluation circuitry, that the guard wire or sense wire is interrupted if the current, l_Sense_Node, is zero.
[0015] Preferably, the diagnostics voltage source is coupled to the first junction via a diagnostics DC blocking element. Preferably, a second EMC filter is connected between the diagnostics voltage source and the diagnostics DC blocking element.
[0016] In one embodiment, a current-to-voltage converter is coupled across the sense node and a guard node of the first EMC filter. Preferably, the method further comprises measuring, using the signal analysis and evaluation circuitry, a voltage output by the current-to-voltage converter and indicating, using the signal analysis and evaluation circuitry, that the guard wire or sense wire is interrupted if a voltage output by the current-to-voltage converter is zero.
[0017] Preferably, the AC voltage signal has a predefined frequency; the method further comprising operating the signal analysis and evaluation circuitry in a frequency selective manner, whereby the detection unit is insensitive to received currents or voltages at frequencies which are not equal to the predefined frequency.
[0018] In one embodiment, the AC voltage signal is amplitude or frequency modulated.
[0019] The invention determines the presence of the sense-guard impedance of a guarded sensor system.
[0020] An advantage of the invention is that, due to the topology of the circuit, conditions of the measurement circuit/detection unit and leading-in the signal for the detection, this concept is insensitive to component variation and external influences.
[0021] Advantages, at least in embodiments, thus include the following: due to the topology of the circuit (detection unit) the diagnostics result is not influenced by component variation and tolerance (EMC-, filter components) or external effects (sense-GND load variation, EMC disturbance).
Brief Description of the Drawings [0022] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:
Figure 1 schematically illustrates a detection arrangement including a detection unit according to an embodiment of the invention, coupled to a guarded sensor; and
Figure 2 shows the detection arrangement of Fig. 1, indicating relevant impedances and current flows.
Description of Preferred Embodiments [0023] In the following, like numerals will be used to indicate like elements.
[0024] Embodiments of the invention are used to determine a wire interruption of a guarded sensor.
[0025] Figure 1 schematically illustrates a detection arrangement 2 including a detection unit 4 according to an embodiment of the invention, in this case in the form of an Electronic Control Unit (ECU), coupled to a guarded sensor 6. In use, a sense wire 8 couples a sense wire output 10 of the detection unit 4 to a sense wire input 12 of the guarded sensor 6, and a guard wire 14 couples a guard wire output 16 of the detection unit 4 to a guard wire input 18 of the guarded sensor 6.
[0026] In this embodiment, the detection unit 4 also includes a first EMC filter 20, the first EMC filter having a sense output 22 coupled to the sense wire output 10 of the detection unit 4 via a sense DC blocking element 24. The first EMC filter 20 also includes a guard output 26 coupled to the guard wire output 16 of the detection unit 4 via a guard DC blocking element 28.
[0027] The first EMC filter 20 has a sense node 30 and a guard node 32, each coupled to signal analysis and evaluation circuitry 34, as will be described in further detail below. In this embodiment, a current-to-voltage converter 36 is coupled across the sense node 30 and a guard node 32 of the first EMC filter 20.
[0028] At least as viewed conceptually, the sensor 6 has (i) an impendence between the sense wire 8 and ground (GND) designated Z_Sense_GND 40, (ii) an impendence between the guard wire 14 and ground designated Z_Guard_GND 42, and (iii) a sense-guard impedance between the sense wire 8 and the guard wire 14 designated Z_Sense_Guard 44.
[0029] In embodiments, the wire interruption detection of the sense and/or guard wire is realized indirect by determining Z_Sense_Guard 44.
[0030] The determination of Z_Sense_Guard 44 is realized by applying an AC signal V2, e.g. from a diagnostics voltage source 46, directly on the guard wire output 16 of the detection unit 4, e.g. to first junction 48 in front of the guard DC blocking element 28, while a DC voltage V1, e.g. from guard voltage source 50, is applied on the guard node 32. Preferably, the diagnostics voltage source 46 is coupled to the first junction 48 via a diagnostics DC blocking element 52. In this embodiment, a second EMC filter 54 is connected between the diagnostics voltage source 46 and the diagnostics DC blocking element 52. In each case, the DC blocking elements described herein may comprise a capacitor.
[0031] In operation, the current to voltage converter 36 mirrors the DC voltage V1 to the sense node 30. Due to DC block (by sense DC blocking element 24 and guard DC blocking element 28) on sense and guard, a DC current flow to the sense output 22 and guard output 26 is not possible and the right side of each of the sense DC blocking element 24 and guard DC blocking element 28 is AC-wise grounded.
[0032] The Figure 2 shows the AC current flow during the diagnostics. The source of the diagnostics current is the voltage source 46 (V2) which applies the AC signal. Via the impedance of the guard DC blocking element 28 the current l_Diagnostics_Source is divided into the AC current (l_Guard_Wire) via the guard wire 14 and the AC current (l_Guard_Node) which flows into the guard node 32. One characteristic of this embodiment is that the diagnostics signal is applied on the left side of the guard DC blocking element 28. Due to this, the impedance of the guard DC blocking element 28 in the guard node 32 is present and acts to divide the diagnostics AC current l_Diagnostics_Source into two parts. One part l_Guard_Node flows into the guard node 32 and a second AC current l_Guard_Wire flows via the guard wire 14 into the sensor 6. A second characteristic of this embodiment is that the guard node 32 and also the sense node 30 are AC-wise grounded. Consequently, an AC current flow via the impedances of the first EMC filter 20 from sense to guard or from guard to Ground is negligible/neglectable. This means that the current l_Guard_Node is not influenced by variation of the EMC filter components.
[0033] The current l_Guard_Wire which flows into the sensor 6 will be divided into two currents. One current (l_Guard_GND) which flows via Z_Guard_GND 42 to ground and a second current (l_Guard_Sense) which flows via Z_Sense_Guard 44 to sense.
[0034] This current (l_Guard_Sense) will be divided again in two parts. One current (l_Sense_GND) which flows via Z_Sense_GND 40 ground and a second current (l_Sense_Wire) which flows via the sense wire 8 and to the impedance of the sense DC blocking element 24 of the detection unit 4.
[0035] Due to the fact that the guard node 32 is AC-wise grounded, the current to voltage converter 36 mirrors the AC ground to the sense node 30. A current flow from the sense node 30 to the guard node 32 is neglectable. This means that the current l_Sense_Node through the current to voltage converter 36 is equal to the current l_Sense_Wire and is not influenced by the first EMC filter 20.
[0036] The final current, which is converted into a voltage by the current to voltage converter 36, is the current l_Sense_Node. This voltage is analysed and evaluated by the signal analysis and evaluation circuitry 34 to determine the sense-guard impedance (Z_Sense_Guard) 44 and diagnose the wire interruption in that way. It can be easily seen that the current l_Sense_Node depends on the impedance Z_Sense_Guard. In the event that the sense wire 8 or guard wire 14 is interrupted, the current l_Sense_Node is zero.
[0037] Another characteristic of this embodiment is that, due to the topology of the diagnostics circuit, the notional impedances Z_Sense_GND and Z_Guard_GND do not influence the current l_Sense_Wire, which is analysed and leads to the diagnostics result. The only impedance which can influence the current l_Sense_Wire, is the impedance of the DC blocking elements 24, 28 and 52 (Z_DC_Block).
[0038] In one embodiment of the invention, the AC signal of the diagnostics signal source 46 has a predefined frequency. As a consequence, the analysis of the current l_Sense_Node by diagnostics circuitry comprising the current to voltage converter 36 and the signal analysis and evaluation circuitry 34 is configured to be frequency selective as well. This makes the techniques according to this embodiment insensitive to frequencies which are not equal to the predefined (diagnostics) frequency.
[0039] In another embodiment, for dealing with the case of sensitivity to remaining external disturbances, modulation methods such as amplitude modulation or frequency modulation can be used in the AC signal.
List of Reference Symbols 2 detection arrangement 4 detection unit 6 sensor 8 sense wire 10 sense wire output 12 sense wire input 14 guard wire 16 guard wire output 18 guard wire input 20 EMC filter 22 sense output 24 sense DC blocking element 26 guard output 28 guard DC blocking element 30 sense node 32 guard node 34 signal analysis and evaluation circuitry 36 current-to-voltage converter
40 Z_Sense_GND
42 Z_Guard_GND 44 Z_Sense_Guard 46 diagnostics voltage source 48 first junction 50 guard voltage source 52 diagnostics DC blocking element 54 EMC filter

Claims (15)

1. Erkennungseinheit (4) zum Erkennen einer Unterbrechung in einem Schutzdraht (14) oder einem Detektionsdraht (8), der einen geschützten Sensor (6) an die Erkennungseinheit (4) anschiießt, wobei die Erkennungseinheit aufweist: einen Detektionsdrahtausgang (10) und einen Schutzdrahtausgang (16), die dafür ausgelegt sind, im Gebrauch an einen Detektionsdraht (8) bzw. einen Schutzdraht (14) angeschlossen zu sein, und ein erstes EMC-Filter (20), wobei das erste EMC-Filter (20) einen Detektionsknoten (30) und einen Schutzknoten (32) aufweist, die jeweils an eine Signalanalyse- und Auswerteschaltung (34) angeschlossen sind, wobei das erste EMC-Filter (20) einen Detektionsdrahtausgang (22) aufweist, der an den Detektionsdrahtausgang (10) der Erkennungseinheit (4) angeschlossen ist; ein Schutz-Gleichstrom-Blockierelement (28), das zwischen einem Schutzdrahtausgang (16) des ersten EMC-Filters (20) und dem Schutzdrahtausgang (16) der Erkennungseinheit (4) angeschlossen ist; eine Schutzspannungsquelle (50), die dafür ausgelegt ist, eine Gleichspannung an den Schutzknoten (32) anzulegen; und eine Diagnosespannungsquelle (46), die dafür ausgelegt ist, ein Wechselspannungssignal an einen ersten Übergang (48) zwischen dem Schutz-Gleichstrom-Blockierelement (28) und dem Schutzdrahtausgang (16) der Erkennungseinheit (4) anzulegen; wobei die Signalanalyse- und Auswerteschaltung (34) dafür ausgelegt ist, anzuzeigen, dass der Schutzdraht (14) oder der Detektionsdraht (8) unterbrochen ist, falls ein Strom aus dem Detektionsknoten (30), l_Sense_Node, null beträgt.A detection unit (4) for detecting an interruption in a guard wire (14) or a detection wire (8) connecting a protected sensor (6) to the detection unit (4), the detection unit comprising: a detection wire output (10) and a Guard wire output (16) adapted to be connected in use to a detection wire (8) and a guard wire (14), respectively, and a first EMC filter (20), wherein the first EMC filter (20) is a detection node (30) and a protection node (32) each connected to a signal analysis and evaluation circuit (34), the first EMC filter (20) having a detection wire output (22) connected to the detection wire output (10) of the detection unit (4) is connected; a protection DC blocking element (28) connected between a guard wire output (16) of the first EMC filter (20) and the guard wire output (16) of the detection unit (4); a protection voltage source (50) adapted to apply a DC voltage to the protection node (32); and a diagnostic voltage source (46) adapted to apply an AC signal to a first junction (48) between the DC protection blocking element (28) and the protective wire output (16) of the detection unit (4); wherein the signal analysis and evaluation circuit (34) is adapted to indicate that the guard wire (14) or the detection wire (8) is interrupted if a current from the detection node (30), l_sense_node, is zero. 2. Erkennungseinheit (4) gemäß Anspruch 1, wobei die Diagnosespannungsquelle (46) über ein Diagnose-Gleichstrom-Blockierelement (52) an den ersten Übergang (48) angeschlossen ist.The detection unit (4) of claim 1, wherein the diagnostic voltage source (46) is connected to the first junction (48) via a diagnostic DC blocking element (52). 3. Erkennungseinheit (4) gemäß Anspruch 2, wobei ein zweites EMC-Filter (54) zwischen der Diagnosespannungsquelle (46) und dem Diagnose-Gleichstrom-Blockierelement (52) angeschlossen ist.The detection unit (4) of claim 2, wherein a second EMC filter (54) is connected between the diagnostic voltage source (46) and the diagnostic DC blocking element (52). 4. Erkennungseinheit (4) gemäß Anspruch 1 oder 2, wobei ein Strom-Spannungs-Wandler (36) über den Detektionsknoten (30) und einen Schutzknoten (32) des ersten EMC-Filters (20) angeschlossen ist.4. detection unit (4) according to claim 1 or 2, wherein a current-voltage converter (36) via the detection node (30) and a protection node (32) of the first EMC filter (20) is connected. 5. Erkennungseinheit (4) gemäß Anspruch 4, wobei die Signalanalyse- und Auswerteschaltung (34) dafür ausgelegt ist, anzuzeigen, dass der Schutzdraht (14) oder der Detektionsdraht (8) unterbrochen ist, falls eine Spannung, die von dem Strom-Spannungs-Wandler (36) ausgegeben wird, null ist.The detection unit (4) according to claim 4, wherein the signal analysis and evaluation circuit (34) is adapted to indicate that the guard wire (14) or the detection wire (8) is broken if a voltage different from the current voltage Converter (36) is output, is zero. 6. Erkennungseinheit (4) gemäß einem der vorstehenden Ansprüche, wobei das Wechselspannungssignal eine vorbestimmte Frequenz hat.A detection unit (4) according to any one of the preceding claims, wherein the AC signal has a predetermined frequency. 7. Erkennungseinheit (4) gemäß Anspruch 6, wobei die Signalanalyse- und Auswerteschaltung (34) dafür ausgelegt ist, in einer frequenzabhängigen Weise zu arbeiten, wobei die Erkennungseinheit (4) gegenüber empfangenen Stromen oder Spannungen bei Frequenzen, die nicht gleich der vorbestimmten Frequenz sind, unempfindlich ist.The detection unit (4) according to claim 6, wherein the signal analysis and evaluation circuit (34) is adapted to operate in a frequency dependent manner, the detection unit (4) being responsive to received currents or voltages at frequencies not equal to the predetermined frequency are insensitive. 8. Erkennungseinheit (4) gemäß einem der vorstehenden Ansprüche, wobei das Wechselspannungssignal ampiituden- Oder frequenzmoduliert ist.8. detection unit (4) according to one of the preceding claims, wherein the AC voltage signal ampiituden- or frequency-modulated. 9. Verfahren (4) zum Erkennen einer Unterbrechung in einem Schutzdraht (14) oder Detektionsdraht (8), der einen geschützten Sensor (6) an die Erkennungseinheit (4) anschließt, wobei das Verfahren aufweist: Bereitstellen einer Erkennungseinheit (4), wobei die Erkennungseinheit aufweist: einen Detektionsdrahtausgang (10) und einen Schutzdrahtausgang (16), die dafür ausgelegt sind, im Gebrauch an einen Detektionsdraht (8) bzw. einen Schutzdraht (14) angeschlossen zu werden, und ein erstes EMC-Filter (20), wobei das erste EMG-Filter einen Detektionsknoten (30) und einen Schutzknoten (32) aufweist, die jeweils an die Signalanalyse- und Auswerteschaltung (34) gekoppelt sind, wobei das erste EMC-Filter (20) einen Detektionsdrahtausgang (22) aufweist, der an den Detektionsdrahtausgang (10) der Erkennungseinheit (4) angeschlossen ist; ein Schutz-Gleichstrom-Blockierelement (28), das zwischen einem Schutzdrahtausgang (16) des ersten EMC-Filters (20) und dem Schutzdrahtausgang (16) der Erkennungseinheit (4) angeschlossen ist; Anlegen, unter Verwendung einer Schutzspannungsquelle (50), einer Gleichspannung an den Schutzknoten (32); und Zuführen, unter Verwendung einer Diagnosespannungsquelle (46), eines Wechselspannungssignals an einen ersten Übergang (48) zwischen dem Schutz-Gleichstrom-Blockierelement (28) und dem Schutzdrahtausgang (16) der Erkennungseinheit (4); Messen, unter Verwendung der Signalanalyse- und Auswerteschaltung (34), eines Stroms aus dem Detektionsknoten (30), l_Sense_Node; und Anzeigen, unter Verwendung der Signalanalyse- und Auswerteschaltung (34), dass der Schutzdraht (14) oder der Detektionsdraht (8) unterbrochen ist, falls der Strom, l_Sense_Node, null beträgt.A method (4) for detecting an interruption in a guard wire (14) or detection wire (8) connecting a protected sensor (6) to the detection unit (4), the method comprising: providing a detection unit (4) the detection unit comprises: a detection wire output (10) and a guard wire output (16) adapted to be connected in use to a detection wire (8) and a guard wire (14), respectively, and a first EMC filter (20), wherein the first EMG filter has a detection node (30) and a protection node (32) each coupled to the signal analysis and evaluation circuit (34), the first EMC filter (20) having a detection wire output (22) connected to the detection wire output (10) of the detection unit (4); a protection DC blocking element (28) connected between a guard wire output (16) of the first EMC filter (20) and the guard wire output (16) of the detection unit (4); Applying, using a protection voltage source (50), a DC voltage to the protection node (32); and supplying, using a diagnostic voltage source (46), an AC signal to a first junction (48) between the protective DC blocking element (28) and the protective wire output (16) of the detection unit (4); Measuring, using the signal analysis and evaluation circuit (34), a current from the detection node (30), l_Sense_Node; and displaying, using the signal analysis and evaluation circuit (34), that the guard wire (14) or the detection wire (8) is broken if the current, l_sense_node, is zero. 10-Verfahren gemäß Anspruch 9, wobei die Diagnosespannungsquelle (46) über ein Diagnose-Gleichstrom-Blockierelement (52) an den ersten Übergang (48) angeschlossen ist.The method of claim 9, wherein the diagnostic voltage source (46) is connected to the first junction (48) via a diagnostic DC blocking element (52). 11. Verfahren gemäß Anspruch 10, wobei ein zweites EMC-Filter (54) zwischen der Diagnosespannungsquelle (46) und dem Diagnose-Gleichstrom-Blockierelement (52) angeschlossen ist.The method of claim 10, wherein a second EMC filter (54) is connected between the diagnostic voltage source (46) and the diagnostic DC blocking element (52). 12. Verfahren gemäß Anspruch 9 oder 10, wobei ein Strom-Spannungs-Wandler (36) über den Detektionsknoten (30) und einen Schutzknoten (32) des ersten EMC-Filters (20) angeschlossen ist12. The method according to claim 9 or 10, wherein a current-voltage converter (36) via the detection node (30) and a protection node (32) of the first EMC filter (20) is connected 13. Verfahren gemäß Anspruch 12, ferner umfassend das Messen, unter Verwendung der Signalanalyse- und Auswerteschaltung (34), einer Spannung, die von dem Strom-Spannungs-Wandler (36) ausgegeben wird, und Anzeigen, unter Verwendung der Signalanalyse- und Auswerteschaltung (34), dass der Schutzdraht (14) oder der Detektionsdraht (8) unterbrochen ist, falls eine Spannung, die von dem Strom-Spannungs-Wandler (36) ausgegeben wird, null beträgt.The method of claim 12, further comprising measuring, using the signal analysis and evaluation circuit (34), a voltage output from the current-to-voltage converter (36) and displaying, using the signal analysis and evaluation circuit (34) that the guard wire (14) or the detection wire (8) is broken if a voltage output from the current-to-voltage converter (36) is zero. 14. Verfahren gemäß einem der Ansprüche 9 bis 13, wobei das Wechselspannungssignal eine vorbestimmte Frequenz hat; wobei das Verfahren ferner das Betreiben der Signalanalyse- und Auswerteschaltung (34) in einer frequenzabhängigen Weise umfasst, wobei die Erkennungseinheit (4) gegenüber empfangenen Stromen oder Spannungen bei Frequenzen unempfindlich ist, die nicht gleich der vorbestimmten Frequenz sind.14. The method of claim 9, wherein the AC signal has a predetermined frequency; the method further comprising operating the signal analysis and evaluation circuit (34) in a frequency dependent manner, wherein the recognition unit (4) is insensitive to received currents or voltages at frequencies not equal to the predetermined frequency. 15.Verfahren nach einem der vorstehenden Ansprüche, wobei das Wechselspannungssignal ampiituden- oder frequenzmoduliert ist.15.A method according to any one of the preceding claims, wherein the AC voltage signal is ampiituden- or frequency modulated.
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