JPH0629825B2 - Leak detection device - Google Patents

Description

Description: (a) Field of Industrial Application The present invention relates to a liquid leakage detection device for detecting leakage of non-insulating liquid such as water or a mixed liquid of water and oil.

(b) Conventional technology For example, in the underfloor of a computer room where many cables are laid, or a storage room for articles that dislike moisture,
There must be no liquid leakage, and the liquid leakage must be detected early to prevent malfunction of the device and damage to articles.

2. Description of the Related Art Conventionally, as a device for detecting liquid leakage, there has been proposed a device including a detection line whose electric characteristic changes due to adhesion of a non-insulating liquid and a detection circuit which detects a change in electric characteristic of the detection line.

(c) Problems to be Solved by the Invention Such a liquid leakage detection device is originally provided as a safety device, and the frequency of occurrence is low, but if a liquid leakage state occurs once, it causes a great deal of damage. It has the characteristic that it is used for potentially dangerous applications. Therefore, the device is required to have high reliability.

Conventionally, in order to maintain the reliability of the device, regular maintenance inspections are performed, but this is mainly to check the damage of the detection line and the looseness of the connection terminal between the leak detection device and the detection line. In order to carry out a full-scale inspection, it is necessary to individually measure the resistance value of each detection line with a measuring instrument, and it takes a long time to measure all the detection lines. There was a problem.

An object of the present invention is to provide a liquid leakage detection device in which the liquid leakage detection device is provided with a test function so that the liquid leakage detection device itself can easily check the state of the liquid leakage detection sensor and the liquid leakage detection device. It is in.

(d) Means for Solving the Problems The present invention provides a leak detection sensor whose electric resistance changes due to the presence of a non-insulating liquid, and a voltage conversion circuit which converts the electric resistance of the leak detection sensor into a DC voltage. A liquid leak including A / D conversion means for converting the output voltage of the voltage conversion circuit into digital data, and a liquid leakage determination means for determining the presence or absence of liquid leakage based on the output data of the A / D conversion means. In the detection device, a dummy resistance having a constant resistance value connected to the voltage conversion circuit and a diagnostic voltage generation circuit for generating a diagnostic constant voltage are provided, and an operation test unit and the liquid leakage determination unit operate. A normal operation mode and a test mode in which the operation test means operates, and the operation test means is configured so that the liquid leakage detection sensor is connected to the voltage conversion circuit. The sensor voltage display means for displaying the output data output from the A / D conversion means, the first switching means for connecting the dummy resistance to the voltage conversion circuit instead of the liquid leakage detection sensor, and the dummy resistance. Is connected to the voltage conversion circuit, the dummy voltage display means for displaying the output data output from the A / D conversion means, and the diagnostic voltage generation circuit in place of the voltage conversion circuit
It is characterized by comprising a second conversion means connected to the D conversion means, and a diagnostic voltage display means for displaying the output data when the diagnostic voltage generation circuit is connected to the A / D conversion means.

(e) Action The configuration of the present invention is shown in FIG. In the figure, the leak detection sensor is, for example, a detection line having two electrode conductors.
The voltage conversion circuit converts the electric resistance of the leak detection sensor into a DC voltage. The A / D conversion means converts the output voltage of the voltage conversion circuit into digital data (output data). The liquid leakage determination means determines the presence / absence of liquid leakage based on the output data output from the A / D conversion means. That is, although the electric resistance value of the liquid leakage detection sensor decreases due to the presence of the non-insulating liquid, the electric resistance value is determined from the output data, and the presence or absence of liquid leakage is determined based on the electric resistance value.

The leak detection device of the present application normally operates as described above.
On the other hand, in the test mode, the sensor voltage display means displays the voltage value (output data) when the liquid leakage detection sensor is connected to the voltage conversion circuit. This makes it possible to test whether the leak detection sensor shows a normal resistance value. When the first switching means is switched, the dummy resistor is connected to the voltage conversion circuit, and the voltage value (output data) of the voltage conversion circuit at that time is displayed by the dummy voltage display means. This makes it possible to determine whether the voltage conversion of the voltage conversion circuit is normal. further,
When the second switching means is switched, the constant voltage generated by the diagnostic voltage generation circuit is applied to the A / D conversion means, and the output data at this time is displayed by the diagnostic voltage display means.
This makes it possible to display whether or not the A / D conversion means is operating normally. As described above, in the test mode, the voltage of each part of the liquid leakage detection device can be displayed using its own detection function, and it can be easily determined whether the operation is normal or not.

(f) Embodiments A block diagram of a water leakage detection device that is an embodiment of the present invention is shown in FIG. 2 (in the embodiments, "leakage" is taken as an example).

In the figure, a portion 20 within a chain double-dashed line is a control unit, to which a display unit 21 and a relay unit 22 are connected. In the control unit 20, 10 is AC200V or AC100
The constant voltage circuit 11 rectifies and smoothes one secondary side output of the transformer 10 and outputs a 5V power supply voltage as a power supply voltage for a logic circuit system, which is a transformer to which a commercial power supply of V is input. . The sensor circuit 12 is a circuit corresponding to the voltage conversion circuit according to the present invention, and has terminals S1 to S.
A DC voltage corresponding to the resistance of the water leak detection sensor connected to 8 is generated. The dummy sensor circuit 13 is a resistance circuit connected instead of the water leak detection sensor. The reference voltage generation circuit 14 is a circuit that generates three types of predetermined constant voltages. The analog switch 15 outputs any one of the input voltage signals A1 to A12 to the A / D converter 16 based on the instruction data from the CPU 17. A /
The D converter 16 corresponds to the A / D conversion means according to the present invention together with the CPU 17, and is composed of a D / A converter and a comparator, and performs successive approximation A / D conversion by the processing of the CPU 17. The CPU 17 is a one-chip microcomputer with a built-in ROM and RAM, and executes signals written in advance in the ROM to output signals to the analog switch 15, the A / D converter 16, the relay drive circuit 18, the display signal drive circuit 19, and the like. Input and output. Relay drive circuit 18
Is composed of two relays and a circuit for driving them, and outputs from the terminal RRC whether or not any of the water leakage detection sensors connected to the terminals S1 to S8 is in the water leakage state, and the terminal S
It is output from the terminal RDC whether or not any of the water leakage detection sensors connected to 1 to S8 is in the disconnection state. The display signal drive circuit 19 outputs a display signal and a relay control signal to the display unit 21 and the relay unit 22 which are connected to the outside. Output terminals for the power supply voltage to the display unit 21 and the relay unit 22 and other input / output terminals for control signals are omitted.

An external plan view of the display unit 21 shown in FIG. 2 is shown in FIG. In the figure, the water leakage display section and the disconnection display section are respectively 8 as indicated by the numbers 1 to 8.
It is a display unit composed of individual LEDs and corresponds to the measured value display means according to the present invention. The numbers 1 to 8 in the figure correspond to the numbers of the water leakage detection sensors connected to S1 to S8 shown in FIG. The power source display section displays the energized state of the commercial power source. The reset switch is a switch that resets the entire device, and by this operation, the device starts execution from the initial routine of the program. The buzzer switch is a switch for selecting whether to generate or prohibit a buzzer sound when a water leakage state or a wire breakage state is detected.

FIG. 4 shows the sensor circuit 12 shown in FIG. 2 and circuits such as a water leak detection sensor connected thereto. As shown in the figure, the terminals S1 to S8 are connected to the detection line SL and the terminating resistor R, respectively.
o is connected. Reference numeral 13 denotes a resistor which constitutes the above-mentioned dummy sensor circuit, and terminals S1 to S8 and this dummy sensor circuit 13 are respectively provided with similar voltage conversion circuits as shown in the drawing. Taking the voltage conversion circuit at the top as an example, the AC voltage generated on the secondary side of the transformer 10 energizes via R1, SL, Ro, and R2. At that time, the power supply voltage is stabilized by the Zener diodes ZD1 and ZD2. ZNR also removes noise generated between terminals. The drop voltage of the resistor R2 is rectified and smoothed by the diode D1 and the capacitor C1, and the resistors R3 and R4 are
Is divided by. Therefore, the output voltage of the voltage conversion circuit becomes a constant voltage when not in the water leak state, and rises in accordance with the decrease in the inter-conductor resistance of the detection line SL when the water leak state occurs. In addition, when the detection line SL is broken, the terminals S1 to S1
When the connection with S8 is disconnected, a closed loop of current is not formed, so that the output voltage of the voltage conversion circuit becomes substantially zero.
Since the resistance value of the dummy sensor circuit 13 is the same as the termination resistance of each detection line (for example, 20 KΩ), a constant voltage is always generated in the output voltage of the voltage conversion circuit.

A circuit diagram of the relay drive circuit 18, the display signal drive circuit 19 and the relay unit 22 shown in FIG.
Shown in the figure. In the figure, P10 to P17 and P24 and P25 of the CPU 17 are a part of the input / output ports and are used here as output ports. A buffer circuit 30 is connected to P10 to P17, and its output is pulled up by eight resistors R5. An AND circuit (negative logic OR circuit) is connected to the output of the buffer 30 by eight diodes D2 and a resistor R6, and the output is input to the D terminals of the D flip-flops 31 and 32. Clock signals are applied to the flip-flops 31 and 32 from the CPU ports P24 and P25, respectively. A transistor Q1 for driving the common leak relay Ry9 is connected to the output of Q of the plip-flop 31 via a gate 33. Further, the transistor Q2 for driving the common disconnection relay Ry10 is connected to the Q output of the flip-flop 32 via the gate 34. The diode D is provided in the flip-flops 31 and 32.
An OR circuit composed of 3, D4 and a resistor R7 is connected. An oscillating circuit 35 outputs a rectangular wave signal when the output of the OR circuit is at "H" level. The transistor Q3 drives the piezoelectric buzzer BZ by the rectangular wave signal output from 35.

In the relay unit 22 shown in the chain double-dashed line, 36 is a short pin for selecting whether to operate this relay unit when a water leakage state is detected or when a disconnection state is detected. If it is connected, it will operate at the time of detecting the water leakage state, and if it is connected between b and c, it will operate at the time of detecting the disconnection state. A transistor circuit including a noise prevention capacitor C2 and transistors Q6 and Q7 is connected to the c terminal of the short pin 36. 37 is an up edge trigger D-type flip-flop array, 38 is a photocoupler array, 39 is a driver array for driving a relay, 40 is an LED array for confirming the operation of the relays Ry1 to Ry8, and Ry1 to Ry8 are in a leaked state or a broken state, respectively. Is a relay that outputs.

Although the display unit 21 shown in FIG. 2 is not shown in FIG. 5, the output terminal P of the buffer circuit 30 is not shown.
16 L's by the signals for 8 lines output from 10 'to P17' and the water leakage / disconnection selection signals output from the output terminals of the transistors Q4 and Q5 and P24 'and P25'.
The ED (see FIG. 3) is dynamically lit.

6 and 7 show examples of waveforms output from the ports P10 to P17 and P24 and P25 of the CPU 17 shown in FIG. As shown in FIG. 6 (A), P
24 and P25 alternately output the "L" level selection signal, and P10 to P17 alternately output the signal for the water leak display and the signal for the disconnection display. Therefore, when neither sensor is in the water leak state or the wire breakage state, P
10 to P17 remain at the “H” level, and none of the LEDs of the display unit are turned on.

As shown in FIG. 6 (B), when any of P10 to P17 is at "L" level, when P24 or P25 falls, the corresponding individual relay is latched. After that, when any of P10 to P17 is at the "L" level and P24 or P25 rises, the common relay R
Buzzer BZ with y9 or Ry10 latched
Is driven. That is, referring to FIG. 5, in the case where the short pin 36 is connected between a and c and P24 falls, Q4 and Q6 are turned on and Q7 is turned off. As a result, the clock input of each flip-flop of the D-type flip-flop array 37 rises, and the output state of the buffer 30 is latched by the D-type flip-flop array 37. For example, CP
If only port P10 of U is at "L" level, D
Only the type flip-flop 37-1 is in the reset state, and the other flip-flops are in the set state. Therefore, the photo coupler 38-1 is turned off, the output of the inverter 39-1 becomes "L" level, and the confirmation LED 40-1 is turned on.
The individual relay Ry1 is turned on. All the other confirmation LEDs and the individual relays are turned off.

Then, when the port P24 of the CPU rises, the D-type flip-flop 31 is triggered to latch the output state of the negative logic OR circuit composed of R6 and D2. In the above example, the flip-flop 31 is in the reset state, and the transistor Q1 turns on the common leak relay Ry9. At the same time, the output of the OR circuit composed of D3, D4 and R7 becomes "H" level, and the output of the oscillation circuit 35 causes the transistor Q3 to drive the buzzer BZ.

FIG. 7 shows an example of control by output signals from the CPU ports P10 to P17 and P24 / P25. Here, the example of (1) is the same as that of FIG. 6 (B), in which the LED of the display unit is turned on during the "L" period of the selection signal, and the individual relay is latched at the fall of the selection signal and rises. Latches the buzzer together with the common relay. In the example of (2), the selection signal is lowered before the data signal is output from P10 to P17, and the selection signal is raised after the output of the data signal is finished, so that the LE of the display unit is activated.
In this example, only D is turned on. (3) is an example in which the individual relays are latched by lowering the selection signal during the output of the data signal, and the common relay is not latched by raising the selection signal after the output of the data signal is completed. (4) is an example in which the common relay and the buzzer are latched by raising the selection signal during the output of the data signal without lowering the selection signal and latching the individual relay before outputting the data signal.

In this way, depending on the signal corresponding to the sensor number output from the ports P10 to P17 of the CPU and the water leak / disconnection selection signal output from the ports P24 and P25, the LED of the display unit and the individual relay R in the relay unit 22.
It is possible to selectively drive y1 to Ry8 and the common relays Ry9 and Ry10 in the control unit.

Now, the processing procedure of the CPU will be described.

FIG. 8 shows the processing procedure of the main routine of the CPU, and FIG. 9 shows the processing procedure of some subroutines.

As shown in FIG. 8 (A), when the power is turned on or the reset switch is operated, the contents of the RAM are first initialized, and whether the RAM operates normally is checked by writing and reading specific data (n
1). If the RAM is not normal, a message indicating that a memory error has occurred is displayed by blinking a predetermined error code on the LED of the disconnection display portion of the display unit (n2 → n3). If there is no abnormality in the RAM, the operation of the display unit is confirmed by sequentially turning on the LEDs of the display unit (n4). Then, read the status of the mode switch (this is connected to the input / output port of the CPU and can be read by the CPU), and if the normal mode other than the test mode is set, check the status of the connected leak detection sensor. The number is read by the sensor number setting switch (which is, for example, a rotary type DIP switch and is connected to the input / output port of the CPU), and it is checked whether it is an appropriate value of 1 to 8 (n6). When the impossible value is set, a sensor number setting error is displayed by blinking a predetermined error code on the LED of the disconnection display portion of the display unit (n7 → n8). If the setting of the number of sensors is OK, thereafter, water leakage and disconnection are sequentially detected. First, the initial value 10 is set to the number SWN to be selected of the analog switch 15 shown in FIG. 2, and the flag FF1 is set (n9 → n10 → n11). (Flag FF1
Is a flag for storing that the setting of the analog switch number is completed. After that, the analog switch having the set analog switch number is selected, A / D conversion is performed, and voltage data X is obtained (n12 → n13). Then, the voltage data corresponding to the analog switch number SWN is compared. Since SWN = 10 at first, it is determined at n15 whether the difference between the voltage data X and the reference value V ₁₀ stored in advance in the ROM in the CPU is within a certain value. When the voltage data X deviates from the reference voltage V ₁₀ by a predetermined value or more, a predetermined error code is displayed blinking on the LED of the disconnection display portion of the display unit (n16). If the value of the voltage data X is normal, the analog switch number SWN is incremented and the input voltage data indicated by that number is checked (n17 → n18 → n5 → ...).
That is, if SWN = 11, the input voltage data is the second
It is determined whether or not it is close to the reference voltage of (n2
0 → n21). If SWN = 12, it is determined whether the input voltage data is close to the third reference voltage (n
22 → n23). If there is a deviation of a certain value or more, an error display is similarly performed (n24, n25).

If the three reference voltages are A / D converted normally, the A / D converter is regarded as normal, and then the analog switch number SWN is set to 9 (n19), and the dummy sensor circuit is connected. Check the output voltage of the voltage conversion circuit. That is, in n27, it is determined whether or not the deviation between the input voltage data X and the reference voltage V ₉ is within a certain range. If it exceeds a certain range, it is considered that the sensor circuit 12 shown in FIG. 2 is not operating normally and an error is displayed (n28). This is, for example, the sensor circuit 12
The cause is that the AC power supply voltage to is abnormal.

If the input voltage from the dummy sensor circuit is normal, then the analog switch number SWN is set to 1 (n29),
After that, the input voltage data obtained by the actual water leak detection sensor is checked. That is, it is determined at n30 whether the input voltage data X is less than the reference value Vd. If it is less than the above, it is considered that the water leak detection sensor is broken, and the corresponding LED of the breakage display section of the display unit is turned on, and if the relay unit is set to the breakage output side by the shorting pin, the corresponding The individual relay to be turned on is latched, and further the common disconnection relay and the buzzer are latched (n31). Further, at n34, it is determined whether the input voltage data X is a value exceeding the reference value Vr. When the reference value is exceeded, it is considered that the water leak detection sensor is in a water leak state, the corresponding LED of the water leak display section of the display unit is turned on, and the relay unit is set to the water leak output side by the short pin. If so, the corresponding individual relay is latched, and further the common leak relay and buzzer are latched (n3
5). These checks the analog switch number SWN
SWN is sequentially incremented until n reaches a preset number of sensors (n32 → n33 → n5 →.
・ ・). If the check of input voltage data is completed for all water leakage detection sensors, the analog switch number SWN
Is set to 10 (n36), and the process returns to the check of the reference voltage.

The above process is repeated. At this time, the analog switch completes one cycle in about 20 msec.

In addition, step n34 in FIG. 8 corresponds to the liquid leakage determination means.

In n5 of FIG. 8 (A), when the mode switch is set to the test mode, the mode is shifted to the test mode and the processing shown in FIG. 8 (C) is performed. Here, the mode switch and n5 correspond to the mode switching means of the present invention. First, read the value of the sensor number setting switch (n
40). The sensor number setting switch in the test mode is used to set the test number and performs various tests according to the value SN. If SN = 0, a D / A converter test is performed (n41 → n42). This is the D / A provided in the A / D converter 16 shown in FIG.
Data that sequentially changes is repeatedly output to the converter. Thus, the function test of the D / A converter is performed by measuring the output waveform of the D / A converter.

If SN is 1 to 8, the input voltage by the water leak detection sensor indicated by the number is displayed on the display unit together with the sensor number (n43 → n44). That is, the corresponding LED of the water leakage indicator is turned on to indicate the sensor number, and the sensor voltage is displayed as an 8-bit binary number using the entire disconnection indicator. If SN = 9, the input voltage from the dummy sensor is displayed together with the normal voltage value (n45 → n46). That is, the entire leak indicator is used to display the output voltage (dummy voltage) of the dummy sensor in an 8-bit binary number, and the disconnection indicator is used to display the normal dummy voltage stored in the CPU 17 as an 8-bit binary number. indicate. SN is 10-1
If it is 2, the input reference voltage and a normal voltage value are compared and displayed (n47 → n48). That is, A of the reference voltage generated by the reference voltage generation circuit
The / D conversion value is displayed in an 8-bit binary number using the entire leak indicator, and the normal reference voltage stored in the CPU 17 is displayed in an 8-bit binary number using the disconnection indicator. If SN = 13, the LEDs of the water leakage display section of the display unit are sequentially turned on and the water leakage common relay is latched (n49 → n50). If SN = 14, the LEDs in the disconnection display portion of the display unit are sequentially turned on and the disconnection common relay is latched (n51 → n52). If SN = 15, each individual relay of the relay unit is sequentially latched (n53). n4
0, n43, n45, n47 and the sensor number setting switch correspond to the first and second switching means of the present invention.

FIG. 9 (A) shows n44, n46, in FIG. 8 (C).
The processing procedure shown in n48 is shown in FIG.
The processing procedures of n50, n52, and n53 in FIG.

As shown in FIG. 9 (A), in the sensor voltage test, first, the LED of the SNth water leakage display section indicated by the value of the sensor number setting switch is turned on (n60). Then, the SNth sensor is selected and the input voltage is A / D converted (n61 →
n62 → n63). Further, the input voltage data is displayed in binary on the LED of the disconnection display portion of the display unit (n64). Thereby, the sensor output voltage is displayed together with the sensor number under test.

In the dummy sensor voltage test, the design normal voltage is displayed in binary on the LED of the water leakage display section of the display unit (n65), and the sensor output voltage of the dummy sensor is displayed in binary on the LED of the disconnection display section of the display unit. It is displayed (n61 to n64). This compares the normal dummy sensor output voltage with the actual output voltage. In the case of the reference voltage test, the design normal voltage value is displayed in binary on the LED of the water leakage display section of the display unit, and the voltage data of the actual reference voltage indicated by SN is displayed on the LE of the display unit disconnection display section.
It is displayed in D in binary (n61 to n64). As a result, the normal reference voltage and the actually read reference voltage are compared and displayed.

In the leak LED and common relay test, as shown in FIG. 9 (B), first, L of the leak indicator of the display unit is displayed.
The initial value 1 is set as the ED number (n70), and the Nth LED of the water leakage display section is lit for 0.7 seconds (n71).
→ n72). Thereafter, the value of n is sequentially incremented until n = 8, and the same processing is repeated (n73 → n74).
→ n71). As a result, the LEDs of the water leakage display section of the display unit are sequentially turned on and the water leakage common relay is latched.

In the disconnection LED / common relay test, the processing shown in FIG. 9 (C) is performed. The difference from the processing shown in FIG. 9B is n
There is only a point of turning on the LED of the disconnection display section of the display unit at 81, and the LEDs of the disconnection display section of the display unit are sequentially turned on by the same processing as the processing shown in FIG. Latch.

In the individual relay test, the processing shown in FIG. 9 (D) is performed.
The difference from the process shown in FIG. 9 (B) is that each individual relay of the relay unit is turned on at n91, and by performing the same process as the process shown in FIG. 9 (B), the relay unit Sequentially turn on each individual relay.

In the embodiment, the voltage conversion circuit is provided corresponding to each of the water leak detection sensor and the dummy sensor circuit connected as the sensor circuit 12. However, for example, a single voltage conversion circuit is used, and a plurality of water leak detections are provided at its input. The sensor and the dummy sensor circuit (dummy resistance) may be sequentially switched and connected.

As described above, in this embodiment, the dummy voltage and the reference voltage (diagnostic voltage) are displayed in parallel with the measured value and the normal value, so that the person performing the test does not have to remember the normal value. Also, it is possible to judge whether these values are normal or not by simply looking at the display unit without referring to other materials.

(g) Effect of the Invention As described above, according to the present invention, since the sensor voltage, the dummy voltage, and the diagnostic voltage can be displayed in the test mode, the staff can use the other measuring devices without using any other measuring device. Only by setting the test mode, it is possible to reliably determine whether or not the liquid leakage detection device is operating normally.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of the present invention. FIG. 2 is a block diagram of a water leak detection device according to an embodiment of the present invention, and FIG. 3 is an external plan view of a display unit of the device. FIG. 4 is a circuit diagram of the sensor circuit 12 shown in FIG. 2 and its peripheral portion. FIG. 5 is a circuit diagram of the blocks 17, 18, 19 and 22 shown in FIG. Sixth
7A and 7B and FIG. 7 are waveform diagrams of signals for the relay drive circuit 18, the display signal drive circuit 19, the display unit 21 and the relay unit 22 shown in FIG. 8A to 8C and 9A to 9D are flowcharts showing the processing procedure of the CPU. 12 ... Sensor circuit (voltage conversion circuit), 13 ... Dummy sensor circuit (dummy resistance), 14 ... Reference voltage generation circuit, Ro ... Termination resistance, SL ... Detection line, (Ro + SL) ... Water leakage detection sensor , Ry1 to Ry8 ... individual relays, Ry9 ... common leak relay, Ry10 ... common disconnection relay, BZ ... piezoelectric buzzer.

Claims (1)

[Claims] 1. A leak detection sensor whose electric resistance changes due to the presence of a non-insulating liquid, a voltage conversion circuit for converting the electric resistance of this leak detection sensor into a DC voltage, and an output voltage of this voltage conversion circuit. A leak detecting device comprising A / D converting means for converting into digital data, and leak judging means for judging presence / absence of leak based on output data of the A / D converting means, wherein the voltage converting circuit includes: A dummy resistance having a constant resistance value to be connected and a diagnostic voltage generating circuit for generating a diagnostic constant voltage are provided, and an operation test means, a normal operation mode in which the liquid leakage determination means operates, and the operation test means. And a mode switching means for switching a test mode in which the liquid leakage detection sensor is connected to a voltage conversion circuit, and the operation test means outputs from the A / D conversion means. When the dummy resistor is connected to the voltage conversion circuit, the sensor voltage display unit displaying the output data to be displayed, the first switching unit connecting the dummy resistor to the voltage conversion circuit in place of the liquid leakage detection sensor, A dummy voltage display means for displaying output data output from the A / D conversion means, and a second switching means for connecting the diagnostic voltage generation circuit to the A / D conversion means instead of the voltage conversion circuit. And a diagnostic voltage display means for displaying output data when the diagnostic voltage generation circuit is connected to the A / D conversion means.