JP6727958B2 - measuring device - Google Patents

Description

The present invention relates to a measuring device that measures at least a resistance value and a voltage value.

As an example of this type of measuring apparatus, the applicant of the present application has already proposed a measuring apparatus (digital multimeter) disclosed in Non-Patent Document 1 below. As disclosed in FIGS. 6 and 7 of Non-Patent Document 1, this measuring device has a pair of input terminals (one COM terminal and one terminal that also serves as a terminal for voltage measurement and a terminal for resistance measurement). Terminal (V/Ω terminal)), an input circuit for voltage measurement connected between the pair of input terminals, and an input circuit for resistance measurement connected between the pair of terminals.

Specifically, as shown in FIG. 3, the measuring device 81 includes a pair of input terminals 82 and 83, a voltage detection unit 84, an A/D conversion unit 85, a thermistor 86, a current supply unit 87, a processing unit 88, and The output unit 89 is provided. One of the input terminals 82 and 83 (the input terminal 82 in this example) is connected to the reference potential (internal ground G) in the device and functions as a COM terminal.

The voltage detection unit 84 detects the inter-terminal voltage V1 between the input terminals 82 and 83 and outputs the detection voltage V2 having a voltage value corresponding to the voltage value of the inter-terminal voltage V1. As an example, the voltage detection unit 84 detects a high-voltage AC voltage or a high-voltage DC voltage input between the input terminals 82 and 83 as the inter-terminal voltage V1, and also divides the voltage to output it as the detection voltage V2. The voltage generated between both ends of the resistance of the circuit and the resistance connected between the input terminals 82 and 83 when the measurement current Im supplied from the current supply unit 87 flows is detected as the inter-terminal voltage V1 and is as it is ( And a low voltage detection circuit for outputting the detection voltage V2 (without voltage division).

As an example, the high voltage detection circuit includes an input resistor 21 connected to the first voltage detection line Lv1 connected to the input terminal 83 and a plurality of (two in this example) ranges provided corresponding to the measurement range. The resistors (voltage dividing resistors) 22 and 23 and the range resistor corresponding to the measurement range to be used among the range resistors 22 and 23 are selectively connected to the first voltage detection line Lv1, and the first voltage detection line Lv1 is also connected. It is provided with four switches 27, 28, 29, 30 for outputting the inter-terminal voltage V1 divided by the range resistor connected to the input resistor 21 and the input resistor 21 as the detection voltage V2 to the A/D converter 85. It is configured. In addition, the low-voltage detection circuit uses the input resistor 24 connected to the second voltage detection line Lv2 connected to the input terminal 83, and the inter-terminal voltage V1 as the detection voltage V2 via the second voltage detection line Lv2 as A/ And a switch 31 for outputting to the D conversion unit 85.

The A/D conversion unit 85 inputs the detection voltage V2 and performs sampling at a predetermined constant sampling cycle to convert the detection voltage V2 into voltage data Dv indicating an instantaneous value of the detection voltage V2 and output the voltage data Dv to the processing unit 88. ..

The current supply unit 87 is configured to be able to supply the measurement current Im (DC constant current whose current value is known) from the output terminal to the current supply line Li by generating an output voltage at the output terminal with the internal ground G as a reference. Has been done. The current supply unit 87 has a low resistance (output resistance) between its output terminal and the internal ground G. Therefore, in order to prevent a large current from flowing into the current supply unit 87 due to the voltage input between the input terminals 82 and 83, the PTC thermistor 86 is provided in the current supply line Li.

The processing unit 88 is configured to include a computer and a memory (neither of which is shown), and executes the instructed measurement process of the voltage measurement process and the resistance measurement process according to an instruction input from an operation unit (not shown). Execute. The output unit 89 is configured by a display device (such as a liquid crystal display device) as an example, and displays the measurement result of each measurement process executed by the processing unit 88 on the screen.

In the measuring device 81, when the operator operates the operation unit (not shown) and outputs an instruction to measure the voltage from the operation unit to the processing unit 88, the processing unit 88 executes the voltage measurement process. In this voltage measurement process, the processing unit 88 shifts the switch 31 in the voltage detection unit 84 to the off state (disconnects the low voltage detection circuit and the A/D conversion unit 85), and the range resistors 22 and 23. Of the switches 27 to 30 for connecting a range resistance corresponding to an appropriate measurement range of the switches to the first voltage detection line Lv1 (a set of switches 27 and 29, and a switch 28, The other pair of switches (the pair of switches 27 and 29, and the other pair of the switches 28 and 30) is shifted to the off state while one of the groups of 30 is turned on (high voltage detection). (The circuit is connected to the A/D converter 85).

In this state, the voltage detection unit 84 sets the voltage (inter-terminal voltage V1) input between the input terminals 82 and 83 to the range resistance (one of the range resistances 22 and 23) and the input resistance 21 corresponding to the measurement range. The voltage is divided by and is output to the A/D conversion unit 85 as the detection voltage V2. The A/D conversion unit 85 converts the detection voltage V2 into voltage data Dv and outputs the voltage data Dv. The processing unit 88 measures (calculates) the inter-terminal voltage V1 based on the voltage data Dv output from the A/D conversion unit 85 and causes the output unit 89 to display it.

Further, in the measuring device 81, when an instruction to measure resistance is output from the operation unit to the processing unit 88 by an operator operating the operation unit, the processing unit 88 executes the resistance measurement process. In this resistance measurement process, the processing unit 88 shifts the switches 27 to 30 in the voltage detection unit 84 to the off state (disconnects the high voltage detection circuit and the A/D conversion unit 85), and switches the switch 31. It is turned on (the low voltage detection circuit and the A/D converter 85 are connected).

In this state, the measurement current Im is supplied from the current supply unit 87 to the resistance as the measurement object connected between the input terminals 82 and 83, so that the resistance between the input terminals 82 and 83 is increased. A voltage generated between both ends of the resistor due to the flow of the measurement current Im is input to the terminal as the terminal voltage V1. The voltage detection unit 84 outputs this inter-terminal voltage V1 directly (without voltage division) to the A/D conversion unit 85 as the detection voltage V2 via the second voltage detection line Lv2, and the A/D conversion unit 85 The detected voltage V2 is converted into voltage data Dv and output. The processing unit 88 measures (calculates) the inter-terminal voltage V1 based on the voltage data Dv output from the A/D conversion unit 85. Further, the processing unit 88 divides the measured inter-terminal voltage V1 by the current value (known) of the measurement current Im to calculate the resistance value of the measurement target and display it on the output unit 89.

Yoshiyuki Miyazawa, Akihiko Miki, Hideki Tomiyama, Seiji Onuma, "3246 Pencil High Tester", Hiki Giho VOL.24 2003 NO.1, [Search June 21, 2016], Internet <URL:https:/ /www.hioki.co.jp/jp/support/download3/〉

However, the above-mentioned measuring device has the following problems to be improved. That is, in this measuring device, the current supply unit 87 is always connected to the input terminal 83 via the current supply line Li, and the output resistance of the current supply unit 87 is generally low as described above. Therefore, for example, when a pair of input terminals 82 and 83 are connected to a pair of commercial power supply lines and a commercial power supply voltage (high voltage such as AC 100 V) between the commercial power supply lines is to be measured, the input terminal 83 It is said that a leakage current may flow in a path from the current supply line Li to the internal ground G (that is, the input terminal 82) via the current supply unit 87, and the leakage breaker installed in the commercial power supply line may fall. There are challenges to improve.

The present invention has been made to solve the above problems, and a main object of the present invention is to provide a measuring device capable of significantly reducing the current value of the leakage current flowing when measuring a high voltage such as a commercial power supply voltage. To do.

In order to achieve the above object, the measuring apparatus according to claim 1 detects a pair of input terminals and a terminal voltage between the pair of input terminals, and outputs a detection voltage corresponding to a voltage value of the terminal voltage. A voltage detection unit, a current supply unit capable of supplying a measurement current between the pair of input terminals, a voltage measurement process for measuring the voltage value based on the detection voltage, and the voltage measurement process when supplying the measurement current. And a processing unit that performs a resistance measurement process that measures a resistance value of a measurement target connected between the pair of input terminals based on the current value of the measured current value and the voltage value measured in A protection resistor having a high resistance value is disposed between one of the input terminals and the current supply unit, and the first switch capable of shifting to any one of a short circuit state and an open state is the protection resistor. And the processing unit executes the voltage measurement process in a state in which the first switch is moved to the open state to measure the voltage value, and the measured voltage value and a predetermined standard. A voltage measuring device that compares the voltage value and shifts the first switch to the short-circuited state to perform the resistance measuring process when the measured voltage value is equal to or lower than the reference voltage value. The unit divides the voltage between the terminals by a voltage dividing circuit and outputs the voltage as the detection voltage, and the second detection directly outputs the voltage between the terminals as the detection voltage without passing through the voltage dividing circuit. Any one of the paths is configured to be selectable, and a second switch capable of shifting to any one of a short circuit state and an open state is interposed in the second detection path, When the processing unit shifts the first switch to the open state, the processing unit causes the voltage detection unit to select the first detection path and shifts the second switch to the open state. When the switch is shifted to the short-circuited state, the voltage detection unit is caused to select the second detection path and the second switch is shifted to the short-circuited state.

The measurement device according to claim 2 is the measurement device according to claim 1 , wherein the processing unit is configured to be capable of performing an inspection process on the first switch when the pair of input terminals is in an open state. In the inspection process, the voltage detection unit is caused to select the first detection path, the second switch is shifted to the open state, and in this state, the first switch is shifted to the open state. A voltage value based on the detected voltage and a voltage value based on the detected voltage when the first switch is brought into a short-circuit state are measured, and the first switch is inspected based on the two measured voltage values.

According to the measuring device of claim 1, while keeping the current supply unit constantly connected to the input terminal (the input terminal not connected to the internal ground), for example, a high-voltage AC voltage or high-voltage such as a commercial power supply voltage is applied. Even when a DC voltage is input between a pair of input terminals and the voltage value is measured, the current value of the leakage current into the current supply unit caused by the input of these high voltage voltages is increased. The protection resistance of the resistance value can significantly reduce (for example, lower than the sensitivity current of the earth leakage breaker). Further, only when the DC voltage input between the input terminals is a low voltage, the first switch is controlled to be in the short-circuited state to short-circuit the protective resistance, whereby the resistor connected between the current supply unit and the input terminal is connected. A resistance measuring process can be performed by supplying a measurement current to the.

Further , according to this measuring device, when a high voltage between terminals is likely to be input between the input terminals, the voltage between the terminals is changed by shifting the first switch and the second switch to the open state. Since it is possible to avoid the situation where is directly input to the processing unit via the second detection path, it is possible to prevent a failure of the processing unit. When the inter-terminal voltage input between the input terminals is a low DC voltage, the first switch and the second switch are shifted to a short-circuit state, and the inter-terminal voltage is divided via the second detection path. Since the voltage can be input to the processing unit without any need, the voltage between terminals can be measured with higher accuracy, and as a result, in the resistance measurement process, the resistance of the resistors connected between the input terminals can be measured based on this voltage between terminals. The resistance value can be measured with high accuracy.

According to the measuring device of the second aspect , since the inspection of the first switch can be performed, a failure occurs due to the failure of the first switch and remaining in the ON state (that is, for example, the commercial power supply voltage When a high-voltage AC voltage or high-voltage DC voltage is input between the input terminals, the current value of the leakage current into the current supply unit exceeds the sensitivity current of the earth leakage breaker, causing the earth leakage breaker to operate. Can be prevented from occurring.

It is a block diagram of the measuring device 1. 6 is a flowchart for explaining the operation of the measuring device 1. It is a block diagram of the conventional measuring device 81.

Hereinafter, an embodiment of a measuring device will be described with reference to the accompanying drawings.

First, the configuration of the measuring device 1 as the measuring device will be described with reference to the drawings.

As shown in FIG. 1, the measuring apparatus 1 includes a pair of input terminals 2 and 3, a voltage detection unit 4, an A/D conversion unit 5, a thermistor 6, protection resistors 7 and 12, a first switch 8, and a current supply unit 9. , A processing unit 10 and an output unit 11. One of the input terminals 2 and 3 (input terminal 2 in this example) is connected to a reference potential (internal ground G) in the device and functions as a COM terminal, and the other (input terminal 3 in this example) is Also serves as a terminal for voltage measurement and a terminal for resistance measurement.

Further, the measuring apparatus 1 is capable of automatic measurement, that is, whether or not an AC voltage (sine wave voltage: E×sin ωt) is automatically input between the input terminals 2 and 3 and whether a DC voltage is input. Whether or not the resistance as the measurement target is connected, whether or not the diode as the measurement target is connected, and when it is determined that the AC voltage is input, measure this voltage value. Also, when it is determined that a DC voltage is input, this voltage value is measured, and when it is determined that a resistor is connected, this resistance value is measured, and the diode is in the forward direction (input terminal 2 When it is determined that the cathode terminal is connected and the anode terminal is connected to the input terminal 3), the forward voltage is measured and each measured value can be output to the output unit 11. ing.

In addition, the specification of the measuring device 1 is, for example, that the measurement voltage range in the higher voltage measurement range is DC±600.0 V for DC voltage and AC600.0 V or less for AC voltage. The measurement voltage range in the middle voltage measurement range is DC±60.00V for DC voltage and AC60.00V or less for AC voltage, and the measurement voltage range in the lower voltage measurement range is The range is DC ±6000 V for DC voltage (excluding a range of 0 V or more and less than +3.000 V) and AC voltage of AC 6.000 V or less. The measurement resistance range in the resistance measurement range is 0Ω to 600.0Ω. Regarding the diode, for example, a Schottky barrier diode having a forward voltage of about 0.35 V, a general-purpose diode having a forward voltage of about 0.6 V, a switching diode having a forward voltage of about 1.2 V, and a forward voltage are In order to be able to measure the forward voltage of various diodes such as light-emitting diodes of about 2V, the voltage range (DC voltage) of the lower voltage measurement range is more than DC+0.3V and less than DC+3V. When it is included in the directional voltage range), it is determined that the diode is connected in the forward direction, and the measured DC voltage is output as the forward voltage.

In this measuring device 1, in order to satisfy the above specifications, each component is configured as follows as an example.

The voltage detection unit 4 detects an inter-terminal voltage V1 between the input terminals 2 and 3 (a voltage generated in the input terminal 3 with the input terminal 2 as a reference potential), and determines the voltage value of the inter-terminal voltage V1. A detection voltage V3 whose voltage value will be described later is output. As an example, the voltage detection unit 4 includes the input resistor 21 provided on the first voltage detection line (first detection path) Lv1 and a plurality of voltage dividing (range) resistors (range) connected to the first voltage detection line Lv1. In this example, as an example, two voltage dividing resistors 22 and 23 which respectively form a voltage dividing circuit together with the input resistor 21), an input resistor 24 interposed in the second voltage detection line (second detection path) Lv2, and The second switch 25, the buffer (or amplifier) 26, and any one of the plurality of voltage dividing resistors (in this example, the two voltage dividing resistors 22 and 23 as described above) are connected to the first voltage detection line Lv1. For selectively connecting to the input terminal of the buffer 26, two switches 27 and 28 for selectively connecting to the input terminal and the connection point of the one selectively connected voltage dividing resistor and the input resistor 21. It is provided with two switches 29 and 30 and one switch 31 for connecting the second voltage detection line Lv2 to the input terminal of the buffer 26. Here, the input resistor 21, each of the voltage dividing resistors 22 and 23, and the switches 27 to 30 configure a high-voltage detection circuit that divides the terminal voltage V1 and outputs the divided voltage, and the input resistor 24, the second switch 25, and the switch 31. Constitutes a low-voltage detection circuit that directly outputs the voltage V1 between terminals without dividing it.

In this case, the input resistors 21 and 24 measure high voltage between the input terminals 2 and 3 (for example, commercial power supply voltage (AC100V (amplitude: 141V) in Japan, AC230V (amplitude: 325V) in Europe and America)). In the state where the voltage having the maximum absolute value in the upper measurement range is input (applied), the leakage current flowing into the measuring device 1 is changed to the operating current of the leakage breaker installed in the commercial power line ( The sensitivity current is defined as a resistance value (for example, 1 MΩ or more) that can be suppressed to less than 30 mA.

The input resistor 21 has one end connected to the input terminal 3 and the other end connected to one end of the voltage dividing resistor 22 via the switch 27 and to one end of the voltage dividing resistor 23 via the switch 28. Has been done. The other ends of the voltage dividing resistors 22 and 23 are connected to the internal ground G. With this configuration, the input resistor 21 is connected to the selected one of the voltage dividing resistors 22 and 23 (the one of the switches 27 and 28 that has been turned on). ), it functions as a voltage dividing resistor that divides the inter-terminal voltage V1 to generate the divided voltage V2. In this example, it is specified to be 10 MΩ. The connection point between the voltage dividing resistor 22 and the switch 27 is connected to the input terminal of the buffer 26 via the switch 29, and the connection point between the voltage dividing resistor 23 and the switch 28 is connected to the buffer 26 via the switch 30. It is connected to the input terminal. Further, the input resistance 24 is specified to be, for example, several MΩ (in this example, 1 MΩ as an example). The resistance value of each of the input resistors 21 and 24 is not limited to this, and can be set to any value as long as the above-mentioned leakage current condition is satisfied.

The voltage dividing resistor 22 is used in the upper measurement range, and in consideration of the input rating of the A/D conversion unit 5 described later (from -10 V to +10 V as an example), the absolute value in this upper measurement range. So that the divided voltage V2 becomes (+10V, -10V) when the inter-terminal voltage V1 is input at a voltage value (+1000V, -1000V) that maximizes (i.e., the input resistor 21 and the voltage dividing resistor 22). So that the voltage division ratio can be divided into 1/100) by 100 kΩ. Further, the voltage dividing resistor 23 is used in the middle measurement range, and in consideration of this input rating of the A/D conversion section 5, the voltage value (in which the absolute value in this middle measurement range is maximum ( When the inter-terminal voltage V1 at +100V, -100V) is input, the divided voltage V2 becomes (+10V, -10V) (that is, the divided voltage value 1/10 by the input resistor 21 and the voltage dividing resistor 23). So that the voltage can be divided into two parts).

The input resistor 24 has one end connected to the input terminal 3 and the other end connected to one end of the second switch 25. The other end of the second switch 25 is connected to the input terminal of the buffer 26 via the switch 31. Therefore, the input resistor 24 and the second switch 25 are connected in series and are interposed in the second voltage detection line Lv2. With this configuration, the second voltage detection line Lv2 outputs the inter-terminal voltage V1 as it is (at the voltage division ratio 1) to the input terminal of the buffer 26 when the switches 25 and 31 are on. Further, the switch 31 selectively connects the second voltage detection line Lv2 to the input terminal of the buffer 26. In this case, the second switch 25 is composed of a high breakdown voltage switch (for example, a high breakdown voltage photomoss relay or a mechanical relay). Further, in this example, as an example, each of the switches 27 to 31 is composed of a semiconductor relay or a semiconductor switch. The switch 31 is connected in series with the second switch 25 interposed in the second voltage detection line Lv2 with the above configuration. Therefore, the switch 31 may be omitted and the second switch 25 may be directly connected to the input terminal of the buffer 26.

The buffer 26 is connected to the divided voltage V2 output from one of the switches 29 and 30 connected to the voltage dividing resistors 22 and 23 connected to the first voltage detection line Lv1 and the second voltage detection line Lv2. One of the inter-terminal voltages V1 output from the switched switch 31 is input in a state where the input impedance is high, and is output to the A/D conversion unit 5 as the detection voltage V3. An input amplifier is provided in the A/D conversion unit 5 as described later, and the buffer 26 may be omitted when the input impedance of the input amplifier is high.

The A/D conversion unit 5 is configured to include, for example, an input amplifier and an A/D converter, which are not illustrated, and detects the detected voltage V3 as an analog signal having a voltage value within the input rating (from -10V to +10V). By inputting and sampling at a predetermined constant sampling period, it is converted into voltage data Dv indicating an instantaneous value of the detected voltage V3 and output to the processing unit 10.

The thermistor 6, the protection resistors 7 and 12, and the first switch 8 are interposed (disposed) in the current supply line Li from the input terminal 3 to the output terminal of the current supply unit 9. Specifically, the thermistor 6 is configured by using a PTC thermistor (positive temperature coefficient thermistor) as an example, and one end thereof is connected to the input terminal 3. One protection resistor 12 is defined to be, for example, several kΩ (in this example, 1 kΩ as an example), and one end thereof is connected to the other end of the thermistor 6. The other protection resistor 7 is defined as, for example, several MΩ (in this example, 1.5 MΩ as an example), one end is connected to the other end of the protection resistor 12, and the other end is connected to the output terminal of the current supply unit 9. (An example of a protective resistor arranged between one of the pair of input terminals and the current supply unit). The first switch 8 is composed of a high breakdown voltage switch similar to the second switch 25, and is connected in parallel to the protection resistor 7.

With this configuration, in the current supply line Li, when the inter-terminal voltage V1 between the input terminals 2 and 3 is a high voltage, the first switch 8 shifts to the off state (open state) as will be described later, which is common. In addition, the current value of the current (leakage current) flowing from the input terminal 3 into the current supply unit 9 having a low output impedance can be limited to a sufficiently small value by the protection resistor 7 having a high resistance value. Further, in the current supply line Li, when the inter-terminal voltage V1 between the input terminals 2 and 3 is a low voltage, the first switch 8 shifts to the ON state (short-circuit state) as will be described later. Even if a high voltage is temporarily applied from the terminal 3, the thermistor 6 instantly generates heat and increases its resistance value, so that an overcurrent flows into the current supply unit 9 (that is, this overcurrent Damage to the current supply unit 9 due to the inflow is avoided. Further, even if a low voltage of, for example, about 10 V is applied between the input terminals 2 and 3 in the ON state of the first switch 8, the current value of the current flowing into the current supply unit 9 is set to about 10 mA by the protection resistor 12. It is possible to limit the current value to less than the above-mentioned sensitivity current.

Although not shown, the voltage applied to the current supply line Li from the input terminal 3 is a power supply voltage (A/D) generated with reference to the internal ground G or an internal ground G by a power source (not shown) in the apparatus. It is also possible to adopt a configuration in which a protection diode for clamping to an operating voltage for components inside the device such as the conversion unit 5, the current supply unit 9 and the processing unit 10) is connected to the current supply line Li.

The current supply unit 9 generates an output voltage based on the internal ground G at the output terminal, so that the measurement current Im (DC constant current whose current value is known. From the output terminal to the current supply line Li. In this example, as an example. , 0.5 mA). In addition, the current supply unit 9 controls the voltage value of the output voltage so that the current value of the measured current Im becomes constant according to the size (resistance value) of the load between the internal ground G and the output terminal. However, the upper limit of this voltage value is defined to a predetermined upper limit voltage value (for example, DC 2.8 V, that is, a voltage that can turn on the diode connected in the forward direction). In addition, in the present example, it is assumed that the current supply unit 9 is always performing the operation of supplying the measurement current Im in the activated state of the measurement apparatus 1.

The processing unit 10 is configured by a computer as an example, and executes the measurement processing 50 shown in FIG. In the voltage measurement process executed in this measurement process 50, the processing unit 10 acquires the voltage data Dv output from the A/D conversion unit 5 and the voltage data Dv of each of the voltage detection lines Lv1 and Lv2. Based on the voltage division ratio (either 1/100, 1/10, or 1) in the voltage detection line used at this time and the amplification factor in the buffer 26 and the A/D conversion unit 5, the voltage between terminals is determined. The voltage value of V1 (hereinafter, also simply referred to as inter-terminal voltage V1) is measured (calculated). Further, in the resistance measurement processing executed in this measurement processing 50, the processing unit 10 divides the voltage data Dv output from the A/D conversion unit 5 and the voltage detection line Lv2 used in this resistance measurement processing. The inter-terminal voltage V1 is measured (calculated) based on the pressure ratio (1) and the amplification factor in the buffer 26 and the A/D conversion unit 5, and the measured inter-terminal voltage V1 and the measured current value Im are measured. Based on (known), the resistance value of the resistor connected between the input terminals 2 and 3 is measured (calculated). In the measurement process 50, the processing unit 10 determines whether the input terminals 2 and 3 are in an open state, a resistor is connected, or a diode is connected in the forward direction based on the measured terminal voltage V1. Whether or not it is in the open state, when it is in the open state, resistance measurement processing is executed in the case of resistance, and its resistance value is measured, and in the case of diode, its forward voltage is measured and displayed on the output unit 11. The processing unit 10 also performs on/off control for the first switch 8, the second switch 25, and the switches 27 to 31. In this example, the configuration in which the A/D conversion unit 5 is disposed outside the processing unit 10 is adopted, but the configuration in which the A/D conversion unit 5 is disposed inside the processing unit 10 (that is, A/D It is also possible to employ a configuration in which the D conversion unit 5 and the processing unit 10 are processing units), and the processing unit in this configuration directly inputs the detection voltage V3, and based on the detection voltage V3, the inter-terminal voltage. The voltage measurement process for measuring V1 and the resistance measurement process are performed based on the inter-terminal voltage V1 based on the detected voltage V3 when the measurement current Im is supplied and the current value of the measurement current Im.

The output unit 11 is configured by a display device such as an LCD, for example, and displays the measurement result (measured voltage value or resistance value) measured in the measurement process executed by the processing unit 10 on the screen. The output unit 11 may be configured by various interface circuits instead of the display device. For example, a configuration in which the output unit 11 is configured by a network interface circuit and transmits the measurement result to an external device via a network may be adopted. it can.

Next, the operation of the measuring device 1 will be described.

In the measurement device 1, in the activated state, the A/D conversion unit 5 executes the sampling operation, the current supply unit 9 supplies the measurement current Im, and the processing unit 10 repeatedly executes the measurement process 50.

In this measurement process 50, the processing unit 10 first shifts the first switch 8 and the second switch 25 to the off state (step 51). Next, the processing unit 10 measures and stores the effective value of the inter-terminal voltage V1 in this state as the inter-terminal voltage Vac_off (step 52), and at the same time, calculates the average value of the inter-terminal voltage V1 between the inter-terminal voltage Vdc_off. Is measured and stored (step 53). When measuring the inter-terminal voltage Vac_off and the inter-terminal voltage Vdc_off, the processing unit 10 sets the voltage data Dv output from the A/D conversion unit 5 for a predetermined period (for example, the inter-terminal voltage V1 is an AC voltage). Sometimes, the AC voltage is acquired for one cycle or more), and the inter-terminal voltage Vac_off and the inter-terminal voltage Vdc_off are calculated (measured) based on the voltage data Dv for one cycle or a plurality of cycles. To do. Further, the processing unit 10 uses the voltage dividing resistor 22 to measure the higher measurement range (switches 27 and 29 are turned on and switches 28 and 30 are turned off, based on the calculated inter-terminal voltage Vac_off and inter-terminal voltage Vdc_off. Range) and a medium measurement range (a measurement range in which the switches 27 and 29 are turned off and the switches 28 and 30 are turned on and the voltage dividing resistor 23 is used), and a final measurement range is selected. The terminal voltage Vac_off and the terminal voltage Vdc_off are calculated (measured).

Next, the processing unit 10 compares the measured inter-terminal voltage Vac_off with the inter-terminal voltage Vdc_off to determine whether the inter-terminal voltage Vac_off exceeds the absolute value of the inter-terminal voltage Vdc_off (step 54). In this case, when an AC voltage is externally input between the input terminals 2 and 3, the processing unit 10 sets the AC voltage as the terminal voltage V1 and measures the terminal voltage Vac_off and the terminal voltage Vdc_off. However, the inter-terminal voltage Vac_off (=E/√2), which is the voltage value of the AC voltage, is measured as 1.11 times the absolute value of the inter-terminal voltage Vdc_off (=2×E/π). .. Further, when a DC voltage is externally input between the input terminals 2 and 3, the processing unit 10 determines the DC voltage as the terminal voltage V1 and measures the terminal voltage Vac_off and the terminal voltage Vdc_off. However, the inter-terminal voltage Vac_off is measured as the same value as the absolute value of the inter-terminal voltage Vdc_off which is the voltage value of the DC voltage.

Also, when neither AC voltage nor DC voltage is input from the outside between the input terminals 2 and 3, is neither a resistor nor a diode connected between the input terminals 2 and 3 (input terminal 2 , 3 is open), or the diodes are connected in the opposite direction (the anode terminal is connected to the input terminal 2 and the cathode terminal is connected to the input terminal 3). During this time, the voltage of the input terminal 3 is regulated to the upper limit voltage value of the current supply unit 9 (DC 2.8V in this example) with the potential of the input terminal 2 as a reference. Therefore, the processing unit 10 measures the inter-terminal voltage Vac_off and the inter-terminal voltage Vdc_off with the inter-terminal voltage V1 as the inter-terminal voltage V1, and the inter-terminal voltage Vac_off is the upper limit voltage value. It is measured as the same value as the absolute value of the inter-terminal voltage Vdc_off indicating (DC 2.8V).

Further, when neither AC voltage nor DC voltage is input from the outside between the input terminals 2 and 3, and the diode is connected between the input terminals 2 and 3 in the forward direction, The voltage of 3 is the forward voltage of this diode with reference to the potential of the input terminal 2 (DC 0.35V for Schottky barrier diode, DC 0.6V for general-purpose diode, DC 1.2V for switching diode, DC 2V for light emitting diode). Degree). Therefore, the processing unit 10 measures the inter-terminal voltage Vac_off and the inter-terminal voltage Vdc_off with the inter-terminal voltage V1 as the forward voltage which is the DC voltage, and the inter-terminal voltage Vac_off is the forward voltage. Is measured as the same value as the absolute value of the inter-terminal voltage Vdc_off.

Therefore, the processing unit 10 determines that the AC voltage is input between the input terminals 2 and 3 only when it is determined that the inter-terminal voltage Vac_off exceeds the inter-terminal voltage Vdc_off in step 54. The measured terminal voltage Vac_off is displayed on the output unit 11 as the voltage value of this AC voltage (step 55), and the process returns to step 51.

On the other hand, when the processing unit 10 determines in this step 54 that the inter-terminal voltage Vac_off does not exceed the absolute value of the inter-terminal voltage Vdc_off (that is, whether a DC voltage is input between the input terminals 2 and 3, If a resistor or a diode is connected or nothing is connected (in an open state), then the absolute value of the inter-terminal voltage Vdc_off becomes the upper limit voltage value (DC 2.8 V) of the current supply unit 9. It is determined whether or not they match (for example, whether or not they are included in a voltage range (upper limit voltage range) of ±several percent around DC 2.8V) (step 56). In this case, as described above, when the absolute value of the inter-terminal voltage Vdc_off is measured as the same value as the upper limit voltage value of the current supply unit 9 (DC 2.8 V in this example), the resistance between the input terminals 2 and 3 is reduced. And the diode are not connected (when the input terminals 2 and 3 are open), or the diodes are connected but in the opposite direction (the input terminal 2 is connected to the anode terminal and the input terminal 3 is connected). The cathode terminal is connected).

Therefore, when it is determined in step 56 that the absolute value of the inter-terminal voltage Vdc_off matches the upper limit voltage value (DC 2.8 V) of the current supply section 9, the processing section 10 determines that the input terminals 2 and 3 are connected to each other. Is an open state (a state in which the diode is connected in the reverse direction) by determining that it is either in the open state or the diode is connected in the reverse direction. Information indicating that is displayed on the output unit 11 (step 57), and the process returns to step 51.

On the other hand, when the processing unit 10 determines in step 56 that the absolute value of the inter-terminal voltage Vdc_off does not match the upper limit voltage value (DC 2.8 V) of the current supply unit 9 (that is, the input terminals 2 and 3). When a DC voltage is input, a resistor is connected, or a diode is connected in the forward direction), the absolute value of the inter-terminal voltage Vdc_off is next defined as a reference voltage. It is determined whether or not the value exceeds the value Vref_dc (step 58). In this example, the reference voltage value Vref_dc is defined as the absolute value of the upper limit value and the lower limit value (6000V in this example) of the measurement voltage range for the DC voltage in the lower voltage measurement range.

In this case, the absolute value of the inter-terminal voltage Vdc_off exceeds the reference voltage value Vref_dc when the DC voltage whose absolute value exceeds 6 V is input between the input terminals 2 and 3, and when the AC voltage whose amplitude is 9.42 V. Is input between the input terminals 2 and 3, and when the AC voltage is input, the process proceeds to step 55 by the determination in step 54. Therefore, in step 58, the inter-terminal voltage Vdc_off is input. The absolute value of V exceeds the reference voltage value Vref_dc only when a DC voltage whose absolute value exceeds 6 V is input between the input terminals 2 and 3. Therefore, when the processing unit 10 determines that the absolute value of the inter-terminal voltage Vdc_off exceeds the reference voltage value Vref_dc, it is determined that the DC voltage having the absolute value exceeding 6 V is input between the input terminals 2 and 3. Then, the measured inter-terminal voltage Vdc_off is displayed on the output unit 11 as a voltage value of the DC voltage (for example, a voltage value with a + sign when the polarity is positive, and a voltage value with a − sign when the polarity is negative). (Step 59), the process returns to step 51. As for each process of steps 58 and 59, instead of the current configuration executed after each process of steps 56 and 57, a configuration executed before each process of steps 56 and 57 can be adopted.

On the other hand, when the processing unit 10 determines in step 58 that the absolute value of the inter-terminal voltage Vdc_off does not exceed the reference voltage value Vref_dc (that is, the inter-terminal voltage V1 generated between the input terminals 2 and 3 is At a low voltage (when the absolute value is a DC voltage equal to or lower than the reference voltage value Vref_dc (6V in this example)), the first switch 8 and the second switch 25 are shifted from the off state to the on state (step 60). In addition, shifting the second switch 25 to the ON state means switching the voltage detection line to be used from the voltage detection line Lv1 to the voltage detection line Lv2 (that is, enabling the lower measurement range). Of the switches 27 to 31 for selecting the measurement range, the switches 27 to 30 are switched to the off state and the switch 31 is switched to the on state. Although both ends of the protection resistor 7 (1.5 MΩ) are short-circuited by the first switch 8 that has been turned on, there is another short circuit between the output terminal of the current supply unit 9 having a low output impedance and the input terminal 3. Since the two protection resistors 12 are provided, the protection resistor 12 suppresses the current (leakage current) flowing from the input terminal 3 to the output terminal of the current supply unit 9 below the sensitivity current of the breaker.

Then, the processing unit 10 measures and stores the average value of the inter-terminal voltage V1 in this state as the inter-terminal voltage Vdc_on in the same manner as the above-described measurement of the inter-terminal voltage Vdc_off (step 61). ..

Subsequently, the processing unit 10 determines whether or not the measured inter-terminal voltage Vdc_on is equal to or lower than the full-scale voltage Vfs in the resistance measurement range (step 62). In this case, as the full-scale voltage Vfs in the resistance measurement range, a resistance having the same resistance value as the upper limit value (600.0Ω) in the measurement resistance range in the resistance measurement range is connected between the input terminals 2 and 3. At this time, the measurement current Im (DC constant current of 0.5 mA) supplied from the current supply unit 9 flows through this resistor to mean the voltage (inter-terminal voltage V1) generated across the resistor. .. Therefore, in this example, the full-scale voltage Vfs is DC+0.3 V (=600×0.5 mA).

When it is determined in step 62 that the inter-terminal voltage Vdc_on is DC 0 volt or higher and the full-scale voltage Vfs (DC+0.3 V) or lower in step 62, the processing unit 10 causes resistance (resistance measurement range) between the input terminals 2 and 3. Is determined to be connected, and resistance measurement processing is executed based on the inter-terminal voltage Vdc_on and the current value (0.5 mA) of the measurement current Im to execute resistance measurement. The resistance value is measured (calculated), the measured resistance value is displayed on the output unit 11 (step 63), and the process returns to step 51.

On the other hand, in step 62, the processing unit 10 determines that the inter-terminal voltage Vdc_on is not within the range of DC 0 V or higher and the full-scale voltage Vfs or lower (that is, the voltage higher than the full-scale voltage Vfs). Or the absolute value is a negative voltage less than the reference voltage value Vref_dc), it is next determined whether the inter-terminal voltage Vdc_on is within the forward voltage range (voltage range exceeding DC+0.3V and less than DC+3V). Is determined (step 64).

When it is determined in step 64 that the inter-terminal voltage Vdc_on is within the forward voltage range, the processing unit 10 determines that the diode is connected between the input terminals 2 and 3 in the forward direction. Then, the inter-terminal voltage Vdc_on is displayed on the output unit 11 as the forward voltage of the diode (step 65), and the process returns to step 51. On the other hand, when the processing unit 10 determines that the inter-terminal voltage Vdc_on is not within the forward voltage range, the inter-terminal voltage Vdc_on is the voltage when the resistor is connected (0 V or more at full scale). Since the voltage is not the voltage Vfs (DC+0.3V) or less) and the voltage when the diode is connected (the voltage within the range of more than DC+0.3V and less than DC+3V), this terminal voltage Vdc_on is set to DC. The voltage is displayed on the output unit 11 as a voltage (step 66), and the process returns to step 51.

As a result, in the measuring device 1, when the processing unit 10 executes the above-described measurement processing 50, when a high voltage or a low voltage AC voltage is input between the input terminals 2 and 3, the voltage value ( The inter-terminal voltage Vac_off) is automatically measured through the high resistance input resistor 21 and displayed on the output unit 11. Further, in this measuring device 1, when the input terminals 2 and 3 are in the open state or when the diodes are connected in the reverse direction, it is automatically detected that these states and the open state is established. The information indicating that is displayed on the output unit 11. Further, in this measuring device 1, when a high-voltage DC voltage (a voltage whose absolute value exceeds the reference voltage value Vref_dc (6 V in this example) is input between the input terminals 2 and 3, the voltage value is high. It is automatically measured through the input resistance 21 of the resistance value and displayed on the output unit 11. Also, a low voltage DC voltage between the input terminals 2 and 3 (a voltage range of -6V or more and less than 0V, and +3V or more). When a DC voltage within one of the voltage ranges less than +6V) is input, the voltage value is not as high as the resistance of the protection resistor 7, but the resistance value that can suppress the leakage current to less than the sensitivity current. Is automatically measured through the protective resistance 12 of the above and displayed on the output unit 11. In addition, in this measuring device 1, when a resistance having a resistance value within the measurement resistance range (0Ω or more and 600.0Ω or less) in the resistance measurement range is connected between the input terminals 2 and 3, the resistance value is automatically set. Is measured and displayed on the output section 11, and when a diode is connected between the input terminals 2 and 3 in the forward direction, the forward voltage is automatically measured and displayed on the output section 11. ..

As described above, in the measuring device 1, when the AC voltage is input between the two input terminals 2 and 3, regardless of whether the AC voltage is the high voltage or the low voltage, the output of the current supply unit 9 is output. In the state in which the high resistance protection resistor 7 is interposed between the terminal and the input terminal 3, it is automatically measured through the high resistance input resistor 21 and displayed on the output unit 11, and Even when the DC voltage is input between the two input terminals 2 and 3 and it is a high voltage (when the voltage exceeds the reference voltage value Vref_dc), the output terminal of the current supply unit 9 and the input terminal 3 In the state in which the protective resistance 7 having a high resistance value is interposed therebetween, it is automatically measured through the input resistance 21 having a high resistance value and displayed on the output unit 11. In the measuring device 1, the processing unit 10 controls the first switch 8 to be in the ON state only when the DC voltage is input between the two input terminals 2 and 3 and the DC voltage is low. The protection resistor 7 is short-circuited and the resistance measurement process is executed.

Therefore, according to this measuring apparatus 1, the current supply unit 9 for automatically detecting whether or not the input terminals 2 and 3 are in the open state is provided with the input terminal 3 (input not connected to the internal ground G). Even when a high-voltage AC voltage such as a commercial power supply voltage or a high-voltage DC voltage is input between the input terminals 2 and 3 and the voltage value is measured, the voltage value is measured. It is possible to significantly reduce the current value of the leakage current generated in the current supply unit 9 due to the input of these high-voltage voltages (for example, to be less than the sensitivity current of the leakage breaker). Further, only when the DC voltage input between the input terminals 2 and 3 is a low voltage, the first switch 8 is controlled to be in the ON state to short-circuit the protective resistor 7, and thereby the current supply unit 9 is connected to the input terminal. The resistance measuring process can be performed by supplying the measurement current Im to the resistance connected between the two and three.

Further, in this measuring device 1, the buffer 26 is directly (as it is) without dividing the voltage V1 between the terminals, and further, the second voltage detection line Lv2 to be output to the A/D conversion section 5 is constituted by a high withstand voltage switch. The second switch 25 is interposed and only when the processing unit 10 determines that the DC voltage input between the input terminals 2 and 3 is a low voltage, the second switch 25 together with the first switch 8 are connected. Is controlled from the off state to the on state, and the inter-terminal voltage V1 is output to the buffer 26.

Therefore, according to this measuring device 1, when there is a possibility that a high terminal voltage V1 is input between the input terminals 2 and 3, the terminal voltage V1 is applied to the switch 31, the buffer 26 and the A/D. Since it is possible to avoid a situation where the voltage is directly input (applied) to the conversion unit 5, it is possible to prevent a failure of the voltage detection unit 4 and a failure of the A/D conversion unit 5. When the inter-terminal voltage V1 input between the input terminals 2 and 3 is a low DC voltage, the inter-terminal voltage V1 is directly input to the buffer 26 via the second voltage detection line Lv2 without being divided. Since the voltage V1 between terminals can be measured (that is, the voltage V1 between terminals can be measured using the lower measurement range), the voltage V1 between terminals can be measured with higher accuracy, and as a result, the resistance measurement process can be performed. Also in the above, the resistance value of the resistor connected between the input terminals 2 and 3 can be measured with high accuracy based on the inter-terminal voltage V1.

In the measuring device 1 described above, the processing unit 10 may be configured to be able to execute the inspection process for the first switch 8 in addition to the voltage measurement process and the resistance measurement process. The inspection process will be described below. Regarding this inspection processing, an operating unit (not shown) is provided in the measuring device 1, and when the input terminals 2 and 3 are in an open state, an operator operates the operating unit to operate the operating unit from the operating unit. It is also possible to adopt a configuration in which the processing unit 10 executes when an instruction to execute the inspection process is output as a result, or when the step 57 in the measurement process 50 is executed (that is, when the input terminals 2 and 3 are It is also possible to employ a configuration in which the processing unit 10 automatically executes when the processing unit 10 determines that the processing unit 10 is in the open state.

In this inspection process, the processing unit 10 first causes the voltage detection unit 4 to select the first voltage detection line Lv1 (that is, shifts either the second switch 25 or the switch 31 to the off state and The control for 27 to 30 is executed to select either the upper measurement range or the middle measurement range). Next, the processing unit 10 measures the voltage value based on the voltage data Dv output from the A/D conversion unit 5 when executing the control on the first switch 8 and shifting to the off state (open state). At the same time, the voltage value is measured based on the voltage data Dv output from the A/D conversion unit 5 when the control for the first switch 8 is executed to shift to the ON state (short circuit state).

Subsequently, the processing unit 10 inspects the first switch 8 based on the two measured voltage values. In this case, the voltage value measured when the processing unit 10 executes the control for shifting the first switch 8 to the off state (open state) is the voltage value measured when the first switch 8 normally shifts to the off state. The upper limit voltage value (DC 2.8 V in this example) of the current supply unit 9 is set to the combined resistance of the thermistor 6, the protection resistors 7 and 12 and the input resistor 21 (the resistance value of the thermistor 6+the resistance value of the protection resistor 7+the protection resistance 12). (The resistance value of the input resistor 21 +the resistance value of the input resistor 21) and one voltage dividing resistor corresponding to the selected measuring range of the voltage dividing resistors 22 and 23 (the first reference value for inspection). Voltage). On the other hand, when the first switch 8 fails and does not normally shift to the off state (while it remains in the on state) despite the execution of the above control on the first switch 8, the measured voltage For the value, the upper limit voltage value of the current supply unit 9 (DC 2.8 V in this example), the combined resistance of the protection resistor 12 and the input resistor 21 (resistance value of the protection resistor 12+resistance value of the input resistor 21), and the above It matches the voltage value of the voltage divided by one voltage dividing resistor (second reference voltage for inspection). Therefore, when the measured voltage value matches the first reference voltage for inspection, the processing unit 10 inspects that the first switch 8 is in a state where it can normally shift to the off state, while the measured value is measured. When the voltage value matches the second reference voltage for inspection, it can be inspected that the first switch 8 is in a state where it cannot normally shift to the off state.

Further, the voltage value measured when the processing unit 10 controls the first switch 8 to shift to the ON state (short circuit state) is the current value when the first switch 8 normally shifts to the ON state. The upper limit voltage value of the supply unit 9 (DC 2.8 V in this example) is set to the combined resistance of the thermistor 6, the protection resistor 12 and the input resistor 21 (resistance value of the thermistor 6 + resistance value of the protection resistor 12 + resistance value of the input resistor 21). ) And the voltage value of the voltage divided by the one voltage dividing resistor (the above-mentioned second reference voltage for inspection). On the other hand, when the first switch 8 fails and does not normally shift to the ON state (while it remains in the OFF state) despite the execution of the above control on the first switch 8, the measured voltage For the value, the upper limit voltage value of the current supply unit 9 (DC 2.8 V in this example) is used as the combined resistance of the thermistor 6, the protection resistors 7 and 12 and the input resistor 21 (resistance value of the thermistor 6 + resistance value of the protection resistor 7 + The resistance value of the protection resistor 12+the resistance value of the input resistor 21) and the voltage value of the voltage divided by the one voltage dividing resistor (the above-described first reference voltage for inspection) match. Therefore, when the measured voltage value matches the second inspection reference voltage, the processing unit 10 inspects that the first switch 8 is in a state where it can normally shift to the ON state, while the measured value is measured. When the voltage value matches the first reference voltage for inspection, it can be inspected that the first switch 8 is in a state where it cannot normally shift to the ON state.

In the above example, the voltage value measured when the control for shifting the first switch 8 to the off state (open state) and the control for shifting the first switch 8 to the on state (short circuit state) are performed. It is checked whether or not the first switch 8 is normal by comparing the voltage values measured at the time of execution with the known first test reference voltage and second test reference voltage that can be calculated in advance. However, the voltage value measured when the first switch 8 is shifted to the off state (open state) and the voltage value measured when the first switch 8 is shifted to the on state (short circuit state) It is also possible to directly compare the measured voltage value, and if it is different, the first switch 8 is normal, and if it is the same, it is possible to adopt a simple configuration for inspecting that the first switch 8 is not normal. ..

In this way, the processing unit 10 adopts a configuration in which the inspection process for the first switch 8 is performed based on the instruction from the operator or automatically, so that the first switch 8 fails and remains in the ON state. (1) When a high-voltage AC voltage such as a commercial power supply voltage or a high-voltage DC voltage is input between the input terminals 2 and 3, the leakage current flowing into the current supply unit 9 is caused. It is possible to prevent the occurrence of the problem that the leakage breaker operates because the value exceeds the sensitivity current of the leakage breaker.

Further, in the above example, in order to facilitate understanding of the invention, description was made by applying specific numerical values to various voltage values and resistance values, but the present invention is not limited to these numerical values, and arbitrary values are used. It can be changed to a numerical value. Further, in the above example, the current supply unit 9 adopts a configuration in which the measurement current Im is constantly supplied (output) to the current supply line Li, but the measurement current Im of the measurement current Im is controlled by the processing unit 10, for example. It is also possible to adopt a configuration in which the supply (output) to the current supply line Li can be turned on/off.

1 Measuring Device 2, 3 Input Terminal 4 Voltage Detection Section 5 A/D Conversion Section 7 Protection Resistance 8 First Switch 9 Current Supply Section 10 Processing Section 21 Input Resistance 22, 23 Voltage Dividing Resistance 25 Second Switch Dv Voltage Data Li Current Supply line Lv1 First voltage detection line Lv2 Second voltage detection line V1 Terminal voltage V2, V3 Detection voltage

Claims (2)

A pair of input terminals, a voltage detection unit that detects a voltage between terminals between the pair of input terminals and outputs a detection voltage according to a voltage value of the voltage between the terminals, and a measurement current between the pair of input terminals. A current supply unit capable of supplying, a voltage measurement process for measuring the voltage value based on the detected voltage and the voltage value measured in the voltage measurement process at the time of supplying the measurement current and the current value of the measurement current. Based on the processing unit for performing a resistance measurement process for measuring the resistance value of the measurement target connected between the pair of input terminals,
A protection resistor having a high resistance value is provided between one of the pair of input terminals and the current supply unit, and a first switch capable of shifting to any one of a short circuit state and an open state is provided. Connected in parallel to the protection resistor,
The processing unit executes the voltage measurement process in a state where the first switch is moved to the open state to measure the voltage value and compares the measured voltage value with a predetermined reference voltage value. Then, when the measured voltage value is equal to or lower than the reference voltage value, a measuring device that shifts the first switch to the short-circuited state to execute the resistance measuring process,
The voltage detection unit divides the voltage between the terminals by a voltage dividing circuit and outputs the voltage as the detection voltage, and outputs the voltage between the terminals directly as the detection voltage without passing through the voltage dividing circuit. Any one of the second detection paths is configured to be selectable, and a second switch capable of shifting to any one of a short circuit state and an open state is interposed in the second detection path. Equipped,
When the processing unit shifts the first switch to the open state, the processing unit causes the voltage detection unit to select the first detection path and shifts the second switch to the open state. when it moves the switch to the short-circuit state, the voltage detecting unit measuring that transitions the second switch causes a selected said second detection path to the short-circuited state to the constant system. The processing unit is configured to be able to perform an inspection process on the first switch when the pair of input terminals is in an open state, and in the inspection process, the first detection path is selected for the voltage detection unit. And the second switch is shifted to the open state, and in this state, the voltage value based on the detection voltage when the first switch is shifted to the open state and the first switch are shifted to the short circuit state. wherein the voltage value is measured based on the detected voltage, measuring apparatus according to claim 1, wherein inspecting the first switch based on two voltage values the measurement of time.

Images