JPH11295363A - Impedance measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a measurement time required for measuring an impedance while avoiding wrong measurements. SOLUTION: This impedance measuring apparatus measures an impedance of an object 2 to be measured on the basis of voltages at both ends of the object 2 which are input through voltage detection probes 42a, 42b in a state while a first a.c. constant current is supplied to the object 2 via current supply probes 41a, 41b, and moreover the apparatus can detect a disconnection of the probes 41a, 41b and probes 42a, 42b. In this case, the apparatus is provided with a.c. constant current sources 9, 10 for connecting a second a.c. constant current having a frequency of an even multiple of a frequency of the first a.c. constant current to the object 2 through the probes 42a, 42b, synchronous wave detection circuits 7, 8 for synchronously detecting the voltages at both ends with a synchronous signal synchronized with the first a.c. constant current, and probe disconnection.non-connection detection circuits 11b, 11c for detecting a disconnection.non-connection of the probes 42a, 42b on the basis of output voltages of the a.c. constant current sources 9, 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impedance measuring apparatus which is capable of measuring an impedance having a resistance, a capacitance and an inductance of an object to be measured according to a so-called four-terminal method.

[0002]

2. Description of the Related Art As this kind of impedance measuring device, a resistance measuring device 51 shown in FIG. 4 is conventionally known. The resistance measuring device 51 shown in FIG. 1 includes a constant current source 52 for supplying a DC constant current measuring current IMDC to the measurement target resistor 2, and a voltage V at each terminal of the measurement target resistor 2.
The measuring unit 53 for measuring the output voltage V0 of the constant current source 52, the measuring unit 53, the switches S1, S2, S3 for switching the conduction path of the measuring current IMDC, and the switches S1 to S3. The measured voltage V51,
C for calculating the resistance value of the resistor 2 to be measured based on V52
A PU (not shown) and a display unit (not shown) for displaying the calculated measurement value are provided.

In the resistance measuring device 51, when measuring the resistance value of the resistance object 2 to be measured, first, current supply probes 41a and 41b and a voltage detection probe 42 are used.
After the connection of the probes 41a, 41b, 42a, and 42b to the measurement target resistor 2, a connection confirmation test is performed on these probes 41a, 41b, 42a, and 42b. Specifically, the CPU sets the switches S3 and S
1 are turned on and off, respectively, and in this state, the measuring unit 53 measures the output voltage V0. Then
The CPU controls the switches S3 and S1 to be in the off state and the on state, respectively, and the measuring unit 53 measures the voltage V51.
Further, the CPU controls the switches S1 and S2 to be in the off state and the on state, respectively, and the measuring unit 53 measures the voltage V52. In this case, if the output voltage V0 has reached the output saturation voltage of the constant current source 52, the probe 41a is disconnected, or is not connected or has a poor contact (hereinafter, the disconnection and the poor contact are collectively referred to as the probe 41a). If the voltage V51 is not the output voltage V0 or a value close to the output voltage V0, it is determined that the probe 42a is disconnected or not connected. If the voltage V52 has reached the output saturation voltage of the constant current source 52, it is determined that the probe 41b is disconnected or not connected. If the voltage V52 is not 0 V or a value close to it, the probe 42b is disconnected. It is determined that there is.

After performing the above connection confirmation test, when it is determined that all the probes 41a, 41b, 42a, and 42b are not disconnected, the resistance value measurement is performed. In this case, the CPU controls the switch S1 and the switch S2 to be alternately and repeatedly turned on to thereby turn on the measuring unit 5.
For 3, the voltage V51 and the voltage V52 are alternately and repeatedly measured. Next, the CPU sequentially calculates the difference voltage between the voltage V51 and the voltage V52, which are measured alternately, and sequentially divides the difference voltage by the current value of the measurement current IMDC. The resistance value is sequentially displayed on the display unit.

[0005]

However, the resistance measuring device 51 has the following problems. That is, in the resistance measuring device 51, the probes 41a, 41b, 42
The connection confirmation tests a and b are performed at the start of the measurement, but are not performed during the resistance value measurement. Therefore, at the start of measurement, all the probes 41a, 41a
Even if b, 42a, and 42b are not disconnected or disconnected, if any probe is disconnected or disconnected during measurement, an erroneous resistance value is displayed on the display unit. There is a problem.

On the other hand, the output voltage V0 measured immediately before the measurement of each measurement target resistor 2 is stored each time, and the connection confirmation test is performed based on the output voltage V0 and the measured voltages V51 and V52 during the measurement. It is possible to do. However, even in this case, each time the resistance value of the measurement target resistor 2 is measured, the connection confirmation test must be performed. Therefore, especially when repeatedly measuring the resistance values of a large number of measurement target resistors 2 in an automatic resistance value inspection or the like, it is necessary to switch and control a plurality of switches S1 to S3. The number of required connection confirmation tests must be greater than the number of resistors to be measured. For this reason, the resistance measuring device 51 has a problem that the measurement cost is increased as a result of the resistance value measurement being lengthened as a whole.

The present invention has been made in view of such a problem, and it is possible to reduce a measurement time required for impedance measurement while avoiding an erroneous measurement due to disconnection or disconnection of a voltage detection probe. It is a main object to provide a simple impedance measuring device.

[0008]

According to another aspect of the present invention, there is provided an impedance measuring apparatus for detecting a voltage in a state where a first AC constant current is supplied to an object to be measured via a current supplying probe. An impedance measuring device configured to measure the impedance of the measurement target based on the voltage between both ends of the measurement target input through the probe, and to detect a disconnection of the current supply probe and the voltage detection probe. An AC constant current source for conducting a second AC constant current, which is an even multiple of the frequency of the AC constant current, to the measurement object via the voltage detection probe; and a first AC constant current. A synchronous detection circuit that synchronously detects the voltage at both ends with a synchronous signal that is synchronized with the AC signal, and a disconnection / unconnection of the voltage detection probe based on the output voltage of the AC constant current source Characterized in that a lobe broken or absent detection circuit.

Generally, in order to detect disconnection / non-connection of a probe, a current for detecting disconnection / non-connection is conducted to the probe, and if the current is not conducted, the probe is disconnected and disconnected. A method of determining that there is is used. When this method is applied to disconnection / unconnection detection of a voltage detection probe during measurement, it is necessary to prevent the current for disconnection / unconnection detection from affecting measurement results.

In this impedance measuring device, first,
In a state where a first AC constant current of a predetermined frequency is being supplied to the measurement object via the current supply probe, the AC constant current source supplies a voltage detection probe with respect to the frequency of the first AC constant current. A second alternating constant current of an even multiple frequency is conducted. Next, a synchronous detection circuit synchronously detects the voltage between both ends of the measurement object with a synchronous signal synchronized with the first AC constant current. Specifically, a signal is generated by multiplying the voltage across the measuring object and the synchronization signal by each other, and the signal is low-pass filtered to output a voltage proportional to the effective resistance or reactance of the measuring object. . In this case, the frequency of the second AC constant current is an even multiple of the frequency of the synchronization signal. Therefore, since the positive cycle period and the negative cycle period of the synchronization signal are each equal to one cycle of the AC constant current, when the multiplication voltage of the current waveform of the AC constant current and the synchronization signal is filtered, the second AC constant current The multiplied voltages corresponding to the positive cycle and the negative cycle, respectively, cancel each other. For this reason, the average value of the voltage proportional to the effective resistance or the reactance is obtained by multiplying the voltage across the measuring object and the synchronizing signal by the multiplication voltage when only the first AC constant current that is the measuring current flows. It is equal to the average value of the filtered voltage. As a result, even if the second AC constant current is applied to the measurement object, the influence on the impedance measurement is eliminated, so that it is necessary to execute a disconnection and disconnection confirmation test of the voltage detection probe independently. In addition, the disconnection / non-connection confirmation test of the voltage detection probe and the impedance measurement can be performed in parallel, and the time for impedance measurement can be reduced.

According to a second aspect of the present invention, in the impedance measuring apparatus according to the first aspect,
The probe disconnection / non-connection detection circuit outputs a detection signal longer than one cycle of the second AC constant current when the output voltage of the AC constant current source is out of a predetermined voltage range, and is capable of retriggering. A circuit is provided.

For example, the output voltage of an AC constant current source that outputs a second AC constant current is rectified and smoothed, and when the rectified and smoothed voltage exceeds a predetermined voltage value, the voltage detecting probe is disconnected / not connected. Can also be detected. However, when the time constant of the smoothing circuit is long, it takes a long time to detect the disconnection of the voltage detection probe. On the other hand, in the voltage detection probe disconnection / unconnection detection circuit, when the voltage detection probe is disconnected / unconnected, the output voltage of the second AC constant current source is out of the predetermined voltage range. ,
A detection signal that is longer than one cycle of the second AC constant current is output. In this case, since the timer circuit can be retriggered, when the output voltage of the second AC constant current source goes out of the predetermined voltage range again in the next cycle, the detection signal is continuously output also in that cycle. Therefore, the timer circuit keeps outputting the detection signal as long as the output voltage of the AC constant current source is out of the predetermined voltage range in each cycle. Therefore, for example, it is possible to avoid erroneous measurement by notifying that the voltage detection probe is disconnected / not connected or by stopping the measurement.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment in which an impedance measuring device according to the present invention is applied to a resistance measuring device will be described below with reference to the accompanying drawings.

As shown in FIG. 1, a resistance measuring apparatus 1 includes an AC constant current source 3 for outputting a first AC constant current according to the present invention, capacitors 4 and 5, a differential amplifier circuit 6, a multiplier 7, and L
PF8, AC constant current sources 9 and 10 for outputting the second AC constant current in the present invention, saturation detection circuits 11a to 11d, A
A / D converter 21, a CPU 22, and a display unit 23 are provided.

The AC constant current source 3 has, for example, a frequency of 1 kHz.
At z, the measuring current IM having the current value I1 is supplied to the measuring object resistor 2 and a rectangular wave synchronizing signal SSYN synchronized with the measuring current IM is output. The capacitor 4 prevents the voltage from being applied to the measuring current IM when the measuring target resistor 2 is a voltage source such as a battery. The capacitor 5 outputs only the AC component of the voltage between both ends of the measurement target resistor 2 to the differential amplifier circuit 6. Multiplier 7 and LP
F8 corresponds to the synchronous detection circuit in the present invention. The AC constant current source 9 conducts an AC constant current I2 of 2 kHz to the probe 42a, and the AC constant current source 10
, A 2 kHz alternating current I3 is conducted.

The saturation detection circuit 11a is a circuit for detecting the output saturation of the AC constant current source 3, and as shown in FIG. A reference voltage source 12a for generating a slightly lower reference voltage VREF1, a comparator 13a for comparing the output voltage V11 with the reference voltage VREF1, and a pulse of 1.2 msec when the output voltage of the comparator 13a becomes a high level voltage. A retriggerable one-shot timer 14a for outputting a saturation detection signal S1 having a width. Saturation detection circuit 1
1b constitutes a probe disconnection / non-connection detection circuit of the present invention in combination with the saturation detection circuit 11c, and detects output saturation of the AC constant current source 9. This saturation detection circuit 11b
As shown in the figure, a reference voltage source 12b that generates a reference voltage VREF2 slightly lower than the positive saturation voltage of the output voltage V12 of the AC constant current source 9, an output voltage V12 and a reference voltage VREF2.
13b comparing the comparator 13 with the comparator 13b
0.6m when the output voltage of b becomes a high level voltage
A retriggerable one-shot timer 14b for outputting a saturation detection signal S2 having a pulse width of sec. The saturation detection circuit 11c is a circuit for detecting the output saturation of the AC constant current source 10, and has a voltage slightly lower than the positive saturation voltage of the output voltage V13 of the AC constant current source 10, as shown in FIG. A reference voltage source 12c that outputs a reference voltage VREF3 of
A comparator 13c for comparing the output voltage V13 with a reference voltage VREF3, and a retriggerable one-shot timer 14c for outputting a saturation detection signal S3 having a pulse width of 0.6 msec when the output voltage of the comparator 13c becomes a high level voltage And

The saturation detecting circuit 11d corresponds to the differential amplifier saturation detecting means of the present invention, and detects the output saturation of the differential amplifier circuit 6. As shown in the figure, the saturation detection circuit 11d includes a reference voltage source 12d that outputs a reference voltage VREF4 slightly lower than the positive saturation voltage of the output voltage V1 of the differential amplifier 6, and an output voltage V1. A comparator 13d for comparing with a reference voltage VREF4 and a retrigger that corresponds to a timer circuit of the present invention and outputs a saturation detection signal S4 having a pulse width of 1.2 msec when the output voltage of the comparator 13d becomes a high level voltage. A one-shot timer 14d.

The CPU 22 calculates the resistance value of the resistor 2 to be measured based on the digital data input via the A / D converter 21 and causes the display 23 to display the calculated resistance value. Further, as described later, when the saturation detection signals S1 to S4 are output from the saturation detection circuits 11a to 11d, the CPU 22 causes the display unit 23 to display information indicating that measurement is impossible.

Next, the measuring operation of the resistance measuring device 1 will be described with reference to the waveform diagram shown in FIG.

First, the probe 41 is connected to the resistor 2 to be measured.
When the measurement start switch (not shown) is operated in a state where the a, 41b, 42a, and 42b are connected, the AC constant current source 3 is connected to the sine wave 1 kHz shown in FIG. The measuring current IM is supplied to the resistor 2 to be measured. At the same time, the AC constant current source 3 generates a rectangular wave synchronizing signal SSYN whose positive and negative amplitude values are the same voltage and whose rising and falling are synchronized with the zero cross point of the measuring current IM (FIG. b) is output to the multiplier 7. On the other hand, the AC constant current sources 9 and 10
An AC constant current I2 and an AC constant current I3 (see FIG. 3 (c)) having a sine wave of 2 kHz synchronized with the synchronizing signal SSYN are output. In this case, the AC constant current I2 is conducted through a path composed of the AC constant current source 9, the capacitor 5, the probe 42a, the resistance to be measured 2, the probe 41b, the ground line, and the AC constant current source 9, and the AC constant current I3 Conducts a path formed by the AC constant current source 10, the probe 42b, the lead wire of the measurement target resistor 2, the probe 41b, the ground line, and the AC constant current source 10. At this time, a combined current of the measuring current IM and the AC constant current I2 is conducted through the measuring resistor 2.

Next, the differential amplifier circuit 6
The output voltage V1 is output by differentially amplifying the voltage between both ends of the measurement target resistor 2 input through the terminals a and 42b.
In this case, for example, assuming that the resistance 2 to be measured is a resistance having only a resistance component, the waveform of the output voltage V1 is 1 kHz flowing through the resistance 2 to be measured, as shown in FIG.
Is a composite waveform of the measuring current IM and the AC constant current I2 of 2 kHz. Next, the multiplier 7 multiplies the output voltage V1 and the synchronizing signal SSYN by each other to generate an output voltage V2. The waveform of the output voltage V2 at this time is shown in FIG.
Since the polarity is inverted in accordance with the positive / negative cycle of the synchronizing signal SSYN shown in FIG.
1 has a full-wave rectified waveform. Next, the LPF 8 filters the output voltage V2 to output a voltage V3 whose voltage value is proportional to the effective resistance of the resistance object 2 to be measured.

In this case, since the positive cycle period A and the negative cycle period B (see FIG. 3B) of the synchronizing signal SSYN are each equal to one cycle of the AC constant current I2 of 2 kHz, the current waveform of the AC constant current I2 is And the synchronizing signal SSYN, the multiplied voltages corresponding to the positive cycle and the negative cycle of the AC constant current I2 cancel each other. Therefore, the average value of the voltage V3 is equal to the average value of the voltage obtained by filtering the multiplied voltage obtained by multiplying the voltage across the measurement target resistor 2 and the synchronizing signal SSYN when the measurement current IM alone flows. Become equal. As a result, even if the AC constant current I2 is passed through the resistor 2 to be measured, the voltage V3
The effect on the mean value of is eliminated.

Next, the A / D converter 21 converts the voltage V3 into digital data and outputs it to the CPU 22. Thereafter, the CPU 22 calculates the resistance value of the measurement target resistor 2 by dividing the digital data by the square of the current value I1 of the measurement current IM. At this time, the AC constant current I2
Is eliminated from the influence on the average value of the voltage V3 caused by the flow of
The resistance value of the measurement target resistor 2 can be accurately measured. Even if the measured resistor 2 contains a reactance component, the effect of the alternating constant current I2 flowing through the measured resistor 2 is similarly eliminated. Even if 2 is not only a pure resistor but also a choke coil or a capacitor, the resistance value can be accurately measured. Then C
The PU 22 causes the display unit 23 to display the calculated resistance value.

Next, the current supply probes 41a, 41
b and the voltage detection probes 42a and 42b are disconnected.
A description will be given of a processing operation when no connection is made or when a high-impedance choke coil or the like is used as the measurement target resistor 2.

First, the processing operation when both probes 41a and 41b are disconnected / not connected will be described. In this case, when one of the probes 41a and 41b is disconnected or disconnected, the conduction path of the measuring current IM is cut off, and the output voltage V11 of the AC constant current source 3 saturates to the power supply voltage. At this time, the output voltage V11 becomes a 1 kHz trapezoidal wave in which the positive and negative instantaneous voltages become the positive and negative power supply voltages. Therefore, in the saturation detection circuit 11a, when the output voltage V11 exceeds the reference voltage VREF1, the comparator 13
a inverts the output level from low level to high level,
As a result, the one-shot timer 14a operates for 1.2 ms.
An output signal S1 having a pulse width of ec is output. At this time,
If the output voltage V11 exceeds the reference voltage VREF1 in each cycle of the measurement current IM, the one-shot timer 14a outputs the output signal S1 each time, so that the output signal S1 is continuously output. In this state, C
The PU 22 causes the display unit 23 to display that the probes 41a and 41b are disconnected and not connected in response to the output signal S1 being output.

Next, both probes 42a and 42b are disconnected.
The processing operation when not connected will be described. in this case,
If either of the probes 42a, 42b is disconnected or unconnected, the conduction path of the AC constant currents I2, I3 is cut off, and the output voltage V1 of the AC constant current sources 9, 10 is cut off.
2. V13 saturates to the power supply voltage. Also in this case, the output voltages V11 and V12 are 2 kHz trapezoidal waves in which the positive and negative instantaneous voltages become the positive and negative power supply voltages. Therefore, in the saturation detection circuit 11b, when the output voltage V12 exceeds the reference voltage VREF2 due to the disconnection / unconnection state of the probe 42a, the comparator 13b inverts the output level from a low level to a high level. The timer 14b outputs an output signal S2 having a pulse width of 0.6 msec. At this time, if the output voltage V12 exceeds the reference voltage VREF2 in each cycle of the AC constant current I2, the output signal S2 is continuously output by the one-shot timer 14b outputting the output signal S2 each time. Continue to be. In this state, the CPU 22 causes the display unit 23 to display that the probe 42a is disconnected / not connected due to the output signal S2 being output. Similarly, in the saturation detection circuit 11c, the output voltage V13 of the AC constant current source 10 is changed to the reference voltage V due to the disconnection / unconnection state of the probe 42b.
If REF3 is exceeded, the one-shot timer 14c outputs the output signal S3, and the CPU 22 causes the display unit 23 to display that the probe 42b is disconnected / not connected.

Next, a description will be given of a processing operation when the measurement target resistor 2 has a high impedance. In this case, the output voltage V1 of the differential amplifier circuit 6 may increase to a saturation voltage due to an increase in the voltage across the measurement target resistor 2. At this time, in the saturation detection circuit 11d, since the output voltage V1 exceeds the reference voltage VREF4 in a cycle of 1 msec, the comparator 13d outputs a high-level signal in a cycle of 1 msec.
d continuously outputs the output signal S4 while being retriggered. Next, when the CPU 22 inputs the output signal S4, the CPU 23 causes the display unit 23 to display that the unmeasurable measurement target resistor 2 has been set as the measurement target.

As described above, according to the resistance measuring device 1, the AC constant current sources 9 and 10 constantly conduct the AC constant currents I2 and I3 to the probes 42a and 42b, and the saturation detection circuits 11b and 11c output the same. By detecting the saturation of the voltages V12 and V13, if the probes 42a and 42b are disconnected or disconnected during the measurement, the probes 42a and 42b
Is displayed on the display unit 23,
Erroneous resistance measurement can be prevented. Further, the saturation detection circuit 11d detects the saturation of the output voltage V1 in the differential amplifier circuit 6, thereby preventing erroneous resistance measurement even when the measurement target resistor 2 is a high impedance measurement target. Can be. Further, the retriggerable one-shot timers 14a to 14d are connected to a saturation detection circuit 11a.
~ 11d, the AC constant current source 3,
Output saturation of the differential amplifiers 9 and 10 and the differential amplifier circuit 6 can be quickly and reliably detected.

Note that the present invention is not limited to the above-described embodiment, and the configuration can be appropriately changed. For example, in the embodiment of the present invention, the independent AC constant current sources 9 and 10 conduct the AC constant currents I2 and I3 to the probes 42a and 42b, respectively, but the present invention is not limited to this. Instead of the AC constant current sources 9 and 10, a single AC constant current source may be used. In particular,
An AC constant current is conducted from the AC constant current source to a conduction path including the capacitor 5, the probe 42a, the measurement target resistor 2, the probe 42b, and the AC constant current source, and the output voltage of the AC constant current source is saturated. What is necessary is just to detect. According to this configuration, the probes 42a, 42 in the disconnected / unconnected state
Although it is difficult to specify 2b, it can be easily configured.

In the embodiment of the present invention, the frequency of the AC constant currents I2 and I3 is set to 2 kHz. However, the present invention is not limited to this, and the AC constant current having an even multiple of the frequency of the measuring current IM is used. Of course, current can be used.

Further, in the embodiment of the present invention, the saturation detecting circuits 11a to 11d output the output voltages V11, V12, V13, and V13.
1 is detected on the positive voltage side, but the present invention is not limited to this. Saturation on the negative voltage side of the output voltages V11, V12, V13, V1 may be detected, or both may be detected. May be detected simultaneously. Further, the saturation detection circuits 11a to 11d can be constituted by rectifying / smoothing circuits and comparators.
In the embodiment of the present invention, the saturation detection signals S1 to S1
4 is separately output to the CPU 22, but a logical sum signal of these saturation detection signals may be generated.

Further, in the embodiment of the present invention, an example in which the effective resistance, which is one mode of the impedance, is measured has been described. However, the present invention is not limited to this.
The present invention can be applied to an impedance meter for measuring capacitance and inductance. In this case, a measurement system for measuring reactance by adding synchronous detection based on a synchronization signal obtained by shifting the phase of the synchronization signal SSYN shown in FIG. 3B by 90 ° is added, and based on the measured effective resistance and reactance. Impedance can be measured.

[0033]

As described above, according to the impedance measuring apparatus of the first aspect, the second AC constant current having an even multiple of the frequency of the first AC constant current is supplied to the voltage detecting probe. By conducting, detecting the disconnection of the voltage detection probe based on the output voltage of the AC constant current source that outputs the second AC constant current, impedance measurement and disconnection / unconnection confirmation processing of the voltage detection probe Can be processed in parallel. As a result, it is possible to avoid erroneous measurement due to disconnection and disconnection of the voltage detection probe, and it is not necessary to perform disconnection and disconnection confirmation processing of the voltage detection probe separately and independently. The required measurement time can be shortened, and thus the measurement cost can be reduced.

According to the impedance measuring apparatus of the present invention, the output voltage of the AC constant current source is out of the predetermined voltage range by using the retriggerable timer circuit in the probe disconnection / non-connection detecting circuit. Can be detected promptly and reliably, and thereby disconnection and disconnection of the voltage detection probe can be promptly and reliably reported.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a resistance measuring device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of saturation detection circuits 11a to 11d in the resistance measuring device according to the embodiment of the present invention.

3A and 3B are waveform diagrams for explaining a resistance measuring operation of the resistance measuring device according to the embodiment of the present invention, wherein FIG. 3A is a current waveform diagram of a measuring current IM, and FIG. 3B is a synchronizing signal SSYN; (C) is a current waveform diagram of the AC constant currents I2 and I3, (d) is a voltage waveform diagram of the output voltage V1, and (e) is a voltage waveform diagram of the output voltage V2.

FIG. 4 is a circuit diagram of a conventional resistance measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resistance measuring device 2 Resistance object to be measured 3 AC constant current source 7 Multiplier 8 LPF 9 AC constant current source 10 AC constant current source 11b Saturation detection circuit 11c Saturation detection circuit 14b One shot timer 14c One shot timer 41a Probe 41b Probe 42a Probe 42b Probe IM Measurement current I2 AC constant current I3 AC constant current V12 Output voltage V13 Output voltage SSYN Synchronous signal S2 Saturation detection signal S3 Saturation detection signal

Claims (2)

[Claims] 1. A measurement object based on a voltage across the measurement object input via a voltage detection probe in a state where a first AC constant current is supplied to the measurement object via a current supply probe. Measure the impedance of
In the impedance measuring device configured to be able to detect the disconnection of the current supply probe and the voltage detection probe, a second AC constant current having an even multiple of the frequency of the first AC constant current An AC constant current source for conducting through the voltage detection probe to the object to be measured, a synchronous detection circuit for synchronously detecting the voltage at both ends with a synchronous signal synchronized with the first AC constant current, An impedance measuring device comprising: a probe disconnection / non-connection detection circuit for detecting disconnection / non-connection of the voltage detection probe based on an output voltage of an AC constant current source. 2. The probe disconnection / non-connection detection circuit,
When the output voltage of the AC constant current source is out of a predetermined voltage range, a timer circuit that outputs a detection signal longer than one cycle of the second AC constant current and can be retriggered is provided. The impedance measuring device according to claim 1, wherein