JP5934563B2 - Electrode failure diagnosis device - Google Patents

Description

  The present invention relates to an electrode failure diagnosis apparatus that diagnoses a failure between electrodes.

  2. Description of the Related Art Conventionally, a capacitance type level sensor that detects a liquid level (liquid level) of a liquid in a tank by detecting a capacitance between electrodes is known.

  The capacitance type level sensor calculates the dielectric constant ε from the capacitance Cr between the dielectric constant correction electrode and the ground electrode, and uses the dielectric constant ε from the capacitance Cp between the liquid level detection electrode and the ground electrode. The liquid level L is detected (see FIG. 2).

  As this type of prior art, Patent Document 1 discloses a capacitance detection circuit that detects capacitance between electrodes. This capacitance detection circuit detects the liquid level (liquid level) by converting the capacitance between the electrodes of the first sensor into a frequency, and converts the capacitance between the electrodes of the second sensor into a frequency. To determine the relative permittivity of the liquid.

JP 2007-278968 A

  However, the conventional electrode failure diagnosis apparatus has the following problems. When measuring by immersing a capacitance type level sensor in a liquid having conductivity, it is necessary to cover the surface of the electrode with an insulating material (insulating coating). This insulating coating insulates the electrode from the liquid.

  However, if the insulation coating is damaged due to changes over time over several years, scratches during manufacturing, pinholes, etc., the electrode and liquid are not completely insulated, and a leak current flows between the electrodes, the appropriate electrode No output can be obtained. That is, it cannot be determined whether the capacitance value is small due to the liquid to be detected or due to conduction (leakage current), and the detected capacitance is not correct.

  For this reason, in order to diagnose the failure between electrodes, changing the structure of an electrode part can be considered, but it becomes complicated.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an electrode failure diagnosis apparatus that can easily perform failure diagnosis between electrodes without changing the configuration of the electrode portion. It is in.

In order to achieve the above-mentioned object, the present invention is characterized by the following (1) to (3).
(1) An electrode failure diagnosis device for diagnosing a failure in which a leakage current flows between electrodes,
An application unit for applying a voltage between the electrodes;
A voltage detector for detecting a voltage between the electrodes;
A comparison unit that compares the detected voltage with a threshold that is a voltage for failure determination;
As a result of the comparison, when the voltage between the electrodes is equal to or lower than the threshold value, a determination unit that determines that a failure has occurred in which a leakage current flows between the electrodes;
Be provided.
(2) An electrode failure diagnosis device having the configuration of (1) above,
A detection circuit for detecting a capacitance between the electrodes;
A switching unit for connecting between the electrodes to the detection circuit or the application unit,
When the detection circuit is connected between the electrodes by the switching unit, the detection circuit detects a capacitance between the electrodes,
When the switching unit connects the electrodes and the application unit, the application unit applies a voltage between the electrodes.
(3) An electrode failure diagnosis device configured as described in (1) or (2) above,
At least one surface of the electrode is covered with an insulating material;
The application unit applies a voltage between the electrodes in a state where the electrodes are immersed in a conductive liquid.

According to the present invention, in a state where a voltage is applied, compares the threshold value and the voltage and fault voltage determined between electrodes, the result of the comparison, when the voltage between the electrodes is below a threshold, between electrodes It is determined that a failure that a leak current flows has occurred . Thereby, the failure diagnosis between electrodes can be easily performed, without changing the structure of an electrode part. Moreover, after confirming that there is no failure between the electrodes, it is possible to measure the capacitance between the electrodes by immersing them in a conductive liquid.

  The present invention has been briefly described above. Further, the details of the present invention will be further clarified by reading through a mode for carrying out the invention described below (hereinafter referred to as “embodiment”) with reference to the accompanying drawings. .

FIG. 1 is a circuit diagram showing a configuration of a detection circuit 10 of a capacitance type level monitor 1 to which an electrode failure diagnosis apparatus according to an embodiment is applied. FIG. 2 is a diagram for explaining the measurement of capacitance by the capacitance type level monitor 1 immersed in a liquid having conductivity. FIG. 3 is a graph showing the time change of the voltage between the electrodes. FIG. 4 is a flowchart showing a failure diagnosis procedure between electrodes.

  An electrode failure diagnosis apparatus according to an embodiment of the present invention will be described with reference to the drawings. The electrode failure diagnosis apparatus of this embodiment is applied to a capacitance level monitor that detects a liquid level (liquid level) in a tank.

  This capacitance type level monitor has an oscillation circuit using a capacitance between the electrodes of the liquid level sensor as a capacitor, and detects the liquid level from the oscillation frequency (period). The capacitance type level monitor has an oscillation circuit that uses the capacitance between the electrodes of the dielectric constant sensor as a capacitor, and detects the dielectric constant (relative dielectric constant) from the oscillation frequency (period). Used for correction when calculating the level.

  First, capacitance measurement using a capacitance level monitor will be described. FIG. 2 is a diagram for explaining the measurement of capacitance by the capacitance type level monitor 1 immersed in a liquid having conductivity. A liquid level sensor 2 and a dielectric constant sensor 6 are accommodated in the tank 9. The liquid level sensor 2 has a liquid level detection electrode 4 and a ground electrode 5 that extend in the vertical direction, respectively, and measures the voltage between the liquid level detection electrode 4 and the ground electrode 5 to obtain its capacitance Cp. To detect. The surface of the liquid level detection electrode 4 is covered with an insulating coating 11. The surface of the ground electrode 5 may be covered with an insulating coating instead of the liquid level detection electrode 4 or together with the liquid level detection electrode 4.

  The dielectric constant sensor 6 has a dielectric constant detection electrode 7 and a ground electrode 8 that are arranged on the bottom side and extend in the vertical direction so as to be always immersed in the liquid in the tank 9. The capacitance Cr is detected by measuring the voltage between the electrode 7 and the ground electrode 8. The surface of the dielectric constant detection electrode 7 is covered with an insulating coating 16. Instead of the dielectric constant detection electrode 7 or together with the dielectric constant detection electrode 7, the surface of the ground electrode 8 may be covered with an insulating coating.

  FIG. 1 is a circuit diagram showing a configuration of a detection circuit 10 of a capacitance level monitor 1 to which an electrode failure diagnosis apparatus according to an embodiment is applied. The detection circuit 10 includes an oscillator 21 including a liquid level sensor 2, an oscillator 23 including a dielectric constant sensor 6, AND gates 26 and 27, counters 28 and 29, and a microcomputer (hereinafter referred to as a CPU) 30.

  The oscillator 21 is a CR oscillator including the liquid level sensor 2, the inverter 32, and the resistor R1. This oscillation frequency is determined by a time constant Cp · R1 obtained by multiplying the capacitance Cp of the liquid level sensor 2 by the resistance value of the resistor R1.

  Similarly, the oscillator 23 is a CR oscillator including the dielectric constant sensor 6, the inverter 34, and the resistor R2 described above. This oscillation frequency is determined by a time constant Cr · R2 obtained by multiplying the capacitance Cr of the dielectric constant sensor 6 by the resistance value of the resistor R2.

  Further, the detection circuit 10 connects the liquid level detection electrode 4 of the liquid level sensor 2 and the power supply voltage (DC voltage) V1 via the resistor R5, and the dielectric constant detection electrode 7 of the dielectric constant sensor 6 and the resistor R6. The switch SW1 that switches the connection with the power supply voltage V1 on / off at the same time is provided. When the switch SW1 is turned on, the liquid level detection electrode 4 is connected to the port P6 of the CPU 30, and the dielectric constant detection electrode 7 is connected to the port P4. In the present embodiment, the case where the DC voltage V1 is applied will be described. However, the power supply voltage may be an AC voltage.

  The detection circuit 10 simultaneously turns on the connection between the liquid level detection electrode 4 of the liquid level sensor 2 and the input terminal of the inverter 32 and the connection between the dielectric constant detection electrode 7 of the dielectric constant sensor 6 and the input terminal of the inverter 34. Switch SW2 for switching to / off. When the switch SW2 is turned on, the liquid level detection electrode 4 is connected to the inverter 32, and the dielectric constant detection electrode 7 is connected to the inverter.

  The switches SW1 and SW2 are exclusively turned on / off by a drive signal output from the CPU 30 via the port P3.

  The output of the oscillator 21 is input to one input terminal of the AND gate 26, and the output of the oscillator 23 is input to one input terminal of the AND gate 27. A reference pulse output from the port P2 of the CPU 30 is input to the other input terminal of the AND gates 26 and 27.

  The output terminal of the AND gate 26 is connected to the input terminal of the counter 28, and the output terminal of the counter 28 is connected to the port P 5 of the CPU 30. Similarly, the output terminal of the AND gate 27 is connected to the input terminal of the counter 29, and the output terminal of the counter 29 is connected to the port P 1 of the CPU 30.

  The CPU 30 is a general-purpose microcomputer incorporating a ROM 36, a RAM 37, a timer 38, and the like. The ROM 36 stores a control program, threshold value V2 (see FIG. 3), a table 36a, and the like which will be described later. In the table 36a, the value of the capacitance Cp of the liquid level sensor 2 corresponding to the liquid level (liquid level) is registered for each relative dielectric constant ε of the liquid.

  Further, the CPU 30 exchanges signals with the system 40 such as a meter.

  An operation of the capacitive level monitor 1 having the above-described configuration will be described. First, a diagnostic method for measuring the voltage between the electrodes will be described. FIG. 3 is a graph showing the time change of the voltage between the electrodes. When the switch SW1 is turned on and the power supply voltage V1 is applied to the liquid level detection electrode 4 of the liquid level sensor 2, the capacitor capacity between the electrodes of the liquid level sensor 2 increases, and the voltage Vp is as shown by the curve a. In addition, the voltage rises as time passes, reaches the vicinity of the power supply voltage V1, and becomes a constant voltage saturated.

  However, when a failure occurs between the electrodes, such as breakage of the insulating coating 11, a leakage current flows between the liquid level detection electrode 4 and the ground electrode 5 in the conductive liquid, and a voltage drop occurs between the electrodes. To do.

  For this reason, the voltage Vp of the liquid level sensor 2 does not reach near the power supply voltage V1, but remains at a saturated constant voltage lower than the threshold V2 before it, as shown by the curve b. Here, the threshold value V2 is a value that can diagnose a failure between the electrodes, and is set to an arbitrary value corresponding to the power supply voltage V1, that is, lower than the power supply voltage V1. Accordingly, it is possible to diagnose that a failure between the electrodes has occurred in the liquid level sensor 2. This also applies to the case where the voltage Vr of the dielectric constant sensor 6 is measured. The time until saturation is reached varies depending on the structure of the sensor, the type of liquid, the degree of immersion, and the like, but the time for performing voltage measurement for failure determination may be sufficient as long as the specification is met.

  FIG. 4 is a flowchart showing a failure diagnosis procedure between electrodes. This operation program is stored in the ROM 36 in the CPU 30 and is periodically executed by the CPU 30.

  First, the CPU 30 outputs a drive signal from the port P3, turns on the switch SW1, and turns off the switch SW2 (step S1). As a result, the power supply voltage V1 is applied to the dielectric constant sensor 6 and the liquid level sensor 2 via the resistors R6 and R5, respectively. The process of step S1 corresponds to an application unit. And CPU30 measures the voltage Vr of the dielectric constant sensor 6 input from the port P4, and measures the voltage Vp of the liquid level sensor 2 input from the port P6 (step S2). The process of step S2 corresponds to a voltage detection unit.

The CPU 30 determines whether or not the measured voltages Vr and Vp satisfy Expression (1), that is, whether or not both of the voltages Vr and Vp are larger than the threshold value V2 (step S3). The process of step S3 corresponds to a comparison unit.
Vp> V2 and Vr> V2 (1)

  When satisfy | filling numerical formula (1), CPU30 judges that the failure between electrodes has not generate | occur | produced in the liquid level sensor 2 and the dielectric constant sensor 6, and the liquid level (liquid level) by the electrostatic capacitance system after step S4 Proceed to the detection process.

  The CPU 30 outputs a drive signal from the port P3, turns off the switch SW1, and turns on the switch SW2 (step S4). This corresponds to the process switching unit in steps S1 and S4.

  The CPU 30 outputs a reference pulse of ON time (0.1 seconds) from the port P2, and inputs it to the other input terminals of the AND gates 26 and 27 (step S5). The AND gate 26 performs a logical product operation of the pulse signal from the oscillator 21 and the reference pulse of the ON time, outputs a pulse signal that has passed only the ON time, that is, the gate time (for example, 0.1 second), and supplies the pulse signal to the counter 28. To do.

  Similarly, the AND gate 27 performs an AND operation on the pulse signal from the oscillator 23 and the reference pulse of the ON time, and outputs a pulse signal that has passed only the ON time, that is, the gate time (for example, 0.1 second), and the counter 29.

  The CPU 30 starts the counting operation of the counter 29, and inputs the number of pulses corresponding to the ON time (0.1 seconds) of the pulse signal input to the counter 29 (step S6).

  The CPU 30 obtains the value of the electrostatic capacitance Cr corresponding to the count value of the input number of pulses, and calculates the relative dielectric constant ε of the liquid (step S7).

  The CPU 30 starts the counting operation of the counter 28, and inputs the number of pulses corresponding to the ON time (0.1 second) of the pulse signal input to the counter 28 (step S8).

  The CPU 30 obtains the value of the capacitance Cp corresponding to the input pulse number count value, refers to the table 36a, and calculates the liquid level (step S9).

  The CPU 30 resets the counters 28 and 29 (step S10), and returns to the process of step S1.

  On the other hand, if the formula (1) is not satisfied in step S3, that is, if at least one of the voltages Vr and Vp is equal to or less than the threshold value V2, the CPU 30 applies an insulating coating to at least one of the liquid level sensor 2 and the dielectric constant sensor 6. It is determined that a failure such as damage has occurred between the electrodes. Then, the CPU 30 outputs an error signal to the system 40 (step S11). The process in step S11 corresponds to a determination unit. Thereafter, the CPU 30 ends this operation.

  According to the electrode failure diagnosis apparatus of the present embodiment, when the DC voltage V1 is applied, the voltage between the electrodes is compared with the threshold value V2, and as a result of the comparison, the voltage between the electrodes is equal to or lower than the threshold value V2. , It is determined that there is a failure between the electrodes. Thereby, the failure diagnosis between electrodes can be easily performed, without changing the structure of an electrode part. Therefore, the quality as a liquid level monitor can be maintained. In addition, since this diagnosis can be performed at the time of manufacturing the liquid level monitor, it can also be used for product shipment inspection.

  The present invention is not limited to the configuration of the above-described embodiment, and any configuration that can achieve the function of the configuration of the present embodiment is applicable.

  For example, in the above embodiment, the capacitance is obtained by frequency conversion, but it may be obtained by measuring a switched capacitor or impedance.

  INDUSTRIAL APPLICATION When diagnosing the failure between electrodes, this invention can perform the failure diagnosis between electrodes easily, without changing the structure of an electrode part, and is useful.

DESCRIPTION OF SYMBOLS 1 Capacitance type level monitor 2 Liquid level sensor 4 Liquid level detection electrode 7 Dielectric constant detection electrode 5, 8 Ground electrode 6 Dielectric constant sensor 9 Tank 10 Detection circuit 11, 16 Insulation coating 21, 23 Oscillator 26, 27 AND gate 28 , 29 Counter 30 Microcomputer (CPU)
32, 34 Inverter 36 ROM
36a Table 37 RAM
38 timer 40 system

Claims (3)

An electrode failure diagnosis device for diagnosing a failure in which leakage current flows between electrodes,
An application unit for applying a voltage between the electrodes;
A voltage detector for detecting a voltage between the electrodes;
A comparison unit that compares the detected voltage with a threshold that is a voltage for failure determination;
As a result of the comparison, when the voltage between the electrodes is equal to or lower than the threshold value, a determination unit that determines that a failure has occurred in which a leakage current flows between the electrodes;
An electrode failure diagnosis apparatus comprising: The electrode failure diagnosis device according to claim 1,
A detection circuit for detecting a capacitance between the electrodes;
A switching unit for connecting between the electrodes to the detection circuit or the application unit,
When the detection circuit is connected between the electrodes by the switching unit, the detection circuit detects a capacitance between the electrodes,
When the switching unit connects between the electrodes and the applying unit, the applying unit applies a voltage between the electrodes. The electrode failure diagnosis device according to claim 1 or 2,
At least one surface of the electrode is covered with an insulating material;
The electrode failure diagnosis apparatus, wherein the application unit applies a voltage between the electrodes in a state where the electrodes are immersed in a conductive liquid.

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