JPH11295362A - Impedance measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an impedance measuring apparatus which can avoid wrong measurements when a measurement condition becomes abnormal. SOLUTION: An impedance measuring apparatus 1 includes an a.c. constant current source 3 for supplying an a.c. constant current to an object 2 to be measured via a current supply probe 41a, a differential amplification circuit 6 for differentially amplifying voltages at both ends of the object 2 which are input through voltage detection probes 42a, 42b, and synchronous wave detection circuits 7, 8 for synchronously detecting an output voltage of the differential amplification circuit 6 on the basis of a synchronous signal synchronous with the a.c. constant current. In this case, at least one of probe disconnection.non- connection detection means 11b, 11c for detecting a disconnection.non-connection of the voltage detection probes 42a, 42b and, a differential amplifier circuit saturation detection means 11d for detecting a saturation of the output voltage of the differential amplifier circuit 6 is provided.

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 an impedance measuring apparatus of this kind, the applicant has already developed a resistance measuring apparatus 51 shown in FIG. The resistance measuring device 51 shown in FIG. 1 includes an AC constant current source 3 that supplies a measuring current IM having a frequency of 1 kHz and a current value I1 to the measuring target resistor 2, and a measuring current IM flowing through the measuring target resistor 2. A differential amplifier circuit 6 for differentially amplifying the voltage at both ends when conducting, an output voltage V51 of the differential amplifier circuit 6 and a synchronizing signal SSYN output from the AC constant current source 3 to multiply the output voltage V52. A multiplier 7 for generating, an LPF (low-pass filter) 8 for filtering the output voltage V52 and outputting a voltage V53, an A / D converter (not shown) for analog-to-digital conversion of the voltage V53, A CPU (not shown) for calculating the resistance value of the resistance object 2 to be measured by dividing the digital data of (1) by the square value of the current value I1;
A display unit (not shown) for displaying the calculated resistance value, and a saturation detection circuit 11a for detecting disconnection of the current supply probes 41a and 41b by monitoring the output voltage of the AC constant current source 3. Have.

In this resistance measuring device 51, probes 41a and 41b for supplying current and a probe 4 for detecting voltage are used.
When a measurement start switch (not shown) is operated in a state where the measurement start switches 2a and 42b are connected to the measurement target resistor 2, the AC constant current source 3
Supplies a measuring current IM to the resistor 2 to be measured via the probes 41a and 41b. In this state, the differential amplifier circuit 6 differentially amplifies the voltage between both ends of the measurement target resistor 2 input via the probes 42a and 42b, thereby outputting the output voltage V51. Thereafter, synchronous detection is performed.
Specifically, first, the multiplier 7 generates an output voltage V52 by multiplying the output voltage V51 and the synchronization signal SSYN by each other. Next, the LPF 8 performs low-pass filtering of the output voltage V52, thereby generating a voltage V53 whose voltage value is proportional to the effective resistance of the measurement target resistor 2 and outputting the voltage V53 to the A / D converter.
An A / D converter converts the voltage V53 into digital data. Thereafter, the CPU divides the digital data by the square value of the current value I1 to calculate the resistance value of the resistor 2 to be measured and to display the calculated resistance value on the display unit.

On the other hand, the resistance object 2 to be measured is a resistance measuring device 5
In the case of a high resistance exceeding the measurable range of 1, the AC constant current source 3 cannot flow the measuring current IM having the current value I1 into the measuring object resistor 2, and outputs the AC voltage saturated to the power supply voltage. Output. In addition, when the probes 41a and 41b are disconnected or the probes 41a and 41b are not connected or have poor contact (hereinafter, unconnected and poor contact are also collectively referred to as "unconnected"), The constant current source 3 outputs an AC voltage saturated up to the power supply voltage. In these cases, the resistance value of the resistor 2 to be measured cannot be accurately measured. Therefore, when the saturation detection circuit 11a detects the output saturation of the AC constant current source 3, the saturation detection signal S51 is sent to the CPU. Output to In this case, the CPU displays on the display unit that the measurement condition is abnormal without calculating the resistance value. This prevents erroneous measurement due to disconnection of the probes 41a and 41b and the like.

[0005]

However, the resistance measuring device 51 developed by the applicant has the following points to be improved. First, when measuring the resistance value of the measurement target resistor 2 having a large reactance such as a choke coil having a small resistance component and a large inductance component, the resistance value may be erroneously measured. It is rare. Specifically, when a measuring current IM shown in FIG. 5A is supplied to a choke coil having a large inductance,
Since the output voltage of the AC constant current source 3 is not saturated, the voltage across the choke coil may become high. For this reason, depending on the output voltage capability of the differential amplifier circuit 6, the waveform of the output voltage V51 may be distorted in a positive high voltage region, for example, as shown in FIG. In this case, the output voltage V
52 is the synchronizing signal SSYN and the output voltage V51 shown in FIG.
Therefore, the output voltage V51 has an ideal waveform W1 without distortion, as shown in FIG.
As compared with, the region of positive high voltage has a distorted waveform W2. Accordingly, since the voltage V53 of the LPF 8 obtained by filtering the output voltage V52 becomes lower than the voltage obtained by filtering the waveform W1, the CPU calculates the resistance value to be lower than the actual resistance value. In this case, since the saturation detection signal S51 is not output from the saturation detection circuit 11a, the CPU displays the erroneously measured resistance value without displaying the measurement condition abnormality. Second, even when the voltage detection probes 42a and 42b are disconnected or not connected, the output voltage V51
Becomes 0 V or unstable. Therefore, also in this case, C
The PU may be erroneously measured, and this improvement is desired.

The present invention has been made in view of such improvements, and has as its main object to provide an impedance measuring apparatus capable of avoiding erroneous measurement when an abnormality occurs in measurement conditions.

[0007]

In order to achieve the above object, an impedance measuring apparatus according to claim 1 comprises: an AC constant current source for supplying an AC constant current to a measurement object via a current supply probe; A differential amplifier circuit for differentially amplifying the voltage between both ends of the measuring object input through the voltage detection probe, and synchronous detection of the output voltage of the differential amplifier circuit based on a synchronous signal synchronized with an AC constant current. In an impedance measuring apparatus having a synchronous detection circuit, a probe disconnection / non-connection detecting means for detecting disconnection / non-connection of a voltage detection probe, and a differential detecting a saturation of an output voltage of a differential amplifier circuit. And at least one of an amplification circuit saturation detection means. In order to more reliably avoid an erroneous measurement, it is preferable to provide a current supply probe disconnection / non-connection detecting means for detecting disconnection / non-connection of the current supply probe.

In this impedance measuring device, when the output voltage of the differential amplifier circuit is saturated and distorted due to the large impedance of the object to be measured, the differential amplifier circuit saturation detecting means detects this. . If the voltage detection probe is disconnected or disconnected,
The disconnection detecting means detects this. Next, when these abnormalities are detected, for example, it is notified that the measurement condition is abnormal. For this reason, erroneous measurement can be avoided.

According to a second aspect of the present invention, in the impedance measuring apparatus of the first aspect,
The differential amplifier saturation detecting means includes a timer circuit which outputs a detection signal longer than one cycle of the AC constant current when the output voltage of the differential amplifier circuit is out of a predetermined voltage range, and is capable of triggering again. It is characterized by having.

For example, the output voltage of the differential amplifier circuit can be rectified and smoothed, and the output saturation of the differential amplifier circuit can be detected when the rectified and smoothed voltage exceeds a predetermined voltage value.
However, when the time constant of the smoothing circuit is long, it takes a long time to detect the saturation of the differential amplifier circuit, and it may be difficult to detect the saturation. On the other hand, in the differential amplifying circuit saturation detecting means, when the output voltage of the differential amplifying circuit is out of the predetermined voltage range, the timer circuit outputs a detection signal longer than one cycle of the AC constant current. In this case, since the timer circuit can be retriggered, when the output voltage of the differential amplifier circuit deviates from the predetermined voltage range again in the next cycle of the AC constant current, 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 differential amplifier circuit is out of the predetermined voltage range in each cycle of the AC constant current. For this reason, for example, by notifying that the measurement condition is abnormal or by stopping the measurement, it is possible to avoid erroneous measurement, and to the measurer, within the measurable resistance value range. It is possible to reliably report whether or not the object is a measurement object.

[0011]

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. The same components as those of the resistance measuring device 51 already developed by the applicant are denoted by the same reference numerals, and redundant description will be omitted.

As shown in FIG. 1, a resistance measuring apparatus 1 comprises an AC constant current source 3, capacitors 4 and 5, a differential amplifier circuit 6, a multiplier 7, an LPF 8, AC constant current sources 9 and 10, a saturation detection circuit. 11a to 11d, an 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 includes an AC constant current source 10 and a saturation detection circuit 1.
1b, 11c in combination with the probe disconnection in the present invention.
It corresponds to a non-connection detecting means. In this case, the AC constant current source 9
Causes an AC constant current I2 of 2 kHz to conduct to the probe 42a, and the AC constant current source 10
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
Reference numeral 1b denotes a circuit for detecting the output saturation of the AC constant current source 9, and as shown in the figure, a reference voltage slightly lower than the positive saturation voltage of the output voltage V12 of the AC constant current source 9. V
A reference voltage source 12b for generating REF2, a comparator 13b for comparing the output voltage V12 with the reference voltage VREF2, and a saturation detection signal S2 having a pulse width of 0.6 msec when the output voltage of the comparator 13b becomes a high level voltage. And a retriggerable one-shot timer 14b for outputting the same. 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 for outputting the reference voltage VREF3, a comparator 13c for comparing the output voltage V13 with the reference voltage VREF3, and a pulse width saturation of 0.6 msec when the output voltage of the comparator 13c becomes a high level voltage. And a retriggerable one-shot timer 14c for outputting the detection signal S3.

The saturation detecting circuit 11d corresponds to the differential amplifier saturation detecting means in 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 of the synchronizing signal SSYN (see FIG. 3B) are each equal to one cycle of the AC constant current I2 of 2 kHz, the current waveform of the AC constant current I2 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 apparatus 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 detecting 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 its 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 of 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, 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.

[0031]

As described above, according to the impedance measuring apparatus of the first aspect, since one or both of the probe disconnection / non-connection detecting means and the differential amplifier circuit saturation detecting means are provided, it is possible to detect the voltage for the voltage detection. It is possible to prevent erroneous measurement under the condition where the probe is disconnected / not connected or the measurement target of high impedance is set as the measurement target.

According to the impedance measuring apparatus of the present invention, the timer circuit capable of retrigger is used for the differential amplifier circuit saturation detecting means, so that the output saturation of the differential amplifier circuit is detected quickly and reliably. Accordingly, it is possible to promptly notify whether or not the impedance of the measurement object can be measured.

[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 resistance measuring device that has been already developed by the applicant.

5A and 5B are waveform diagrams for explaining a resistance measuring operation of a resistance measuring device which has already been developed by the applicant, where FIG. 5A is a current waveform diagram of a measuring current IM, and FIG. 5B is a synchronizing signal SSYN. (C) is a voltage waveform diagram of the output voltage V51,
(D) is a voltage waveform diagram of the output voltage V52.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resistance measuring device 2 Resistance object to be measured 3 AC constant current source 6 Differential amplifier circuit 7 Multiplier 8 LPF 9 AC constant current source 10 AC constant current source 11a Saturation detection circuit 11b Saturation detection circuit 11c Saturation detection circuit 11d Saturation detection circuit 14d One-shot timer 41a Probe 41b Probe 42a Probe 42b Probe IM Measurement current I2 AC constant current I3 AC constant current V1 Output voltage V11 Output voltage VREF4 Reference voltage SSYN Synchronization signal S4 Saturation detection signal

Claims (2)

[Claims] 1. An AC constant current source for supplying an AC constant current to a measurement object via a current supply probe, and a differential amplification of a voltage between both ends of the measurement object input via a voltage detection probe. And a synchronous detection circuit that synchronously detects an output voltage of the differential amplification circuit based on a synchronization signal synchronized with the AC constant current. A probe disconnection / non-connection detecting means for detecting disconnection / non-connection of the probe; and a differential amplifier circuit saturation detecting means for detecting a saturation of the output voltage of the differential amplifier circuit. And an impedance measuring device. 2. The differential amplifier saturation detecting means outputs a detection signal longer than one cycle of the AC constant current when an output voltage of the differential amplifier is out of a predetermined voltage range. 2. The impedance measuring apparatus according to claim 1, further comprising a timer circuit capable of retriggering.