JPH0527008Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention relates to a resistance meter that uses alternating current as a measurement signal source.

PRIOR ART

When direct current is applied to the object to be measured, such as when measuring the contact resistance of a relay contact through which a constant direct current is flowing or measuring the internal resistance of a battery, an ohmmeter that uses direct current as the measurement signal source cannot measure it. Since this is difficult, a resistance meter equipped with an AC measurement signal source is used.

This type of resistance meter includes, for example, an AC constant current source 1 as a measurement signal source, as shown in FIG.
A constant measurement alternating current is superimposed and passed through a resistor to be measured 3 through which a direct current is being passed from a direct current power supply 2. As a result, a DC voltage due to the DC current from the DC power source 2 and an AC voltage due to the constant AC current for measurement from the AC constant current source 1 are generated in a superimposed manner between both ends of the resistor 3 to be measured. Of these two voltages, the DC voltage is blocked by, for example, a capacitor C, and the AC voltage is applied to the measuring section 4 via the capacitor C and the isolation transformer T.

Here, the constant current for measurement flowing from the AC constant current source 1 is I, and this current I is applied to the resistor 3 to be measured.
Assuming that currents I ₁ and I ₂ are shunted to the capacitor C and transformer T sides, respectively, a voltage V _X is generated across the resistor 3 to be measured due to the current I ₁ . In addition, a voltage V C and a voltage V _C are applied between the two poles of the capacitor C and the input side of the transformer T, respectively, due to the current I ₂ .
V _L occurs.

This voltage V _L is measured in the measuring section 4, and the value of the current I ₂ is thereby determined. Therefore, the voltage V _C generated across capacitor C is found, and this voltage
The voltage V _X across the resistor 3 to be measured is determined from V _L and V _C. Further, the current I 1 is determined from the difference between the current I from the AC constant current source 1 and _the above-mentioned current I ₂ . Thereby, the resistance value R _X of the resistor 3 to be measured is obtained by calculating R _X =V _X ÷I ₁ .

I would like to provide some additional explanation regarding the above. If the reactance of capacitor C is X _C and the reactance seen from the input side of transformer T is X _L , then the above voltages V _C and V _L generated by current I ₂ are as follows: V・_C = −jX _C・I・₂ V・_L =jX _L・I・₂ ...(1).

However, X _C =-1/C X _L =ωL (2). Here, C is a reference symbol of a capacitor, but for convenience, it is assumed that it represents its capacitance, and L represents the equivalent inductance seen from the input side of the transformer T.

In the above equations (1) and (2), since the frequency of the measurement current I sent from the AC constant current source 1 is determined in advance, the values of the reactances X _C and X _L are known. Therefore, when the voltage V _L in equation (1) is measured by the measuring unit 4, the value of the current I ₂ is determined, and accordingly, the voltage
V _C is also required.

The sum of these two voltages V _C and V _L is the resistor 3 to be measured.
Since _{it is equal} to the voltage _{across both ends of} V

In this case, if the reactance X _C of the capacitor C is the reactance X _L of the transformer T, then X _C ≪X _L
If it is set as follows, equation (3) becomes V・_X = jX _L・I・₂ = V・_L ...(4) |V・_X |=|V・_L | ...( 4)′ can be set. Therefore, the magnitude of the voltage V _L measured by the measuring section 4 can be considered to be equal to the voltage V _X across the resistor 3 to be measured.

Next, since the current I ₁ shunted to the resistor to be measured 3 and the current I ₂ have a phase difference of π/2 from equation (4), the measurement current I flowing from the AC constant current source 1
is the sum of currents I ₁ and I ₂ .

In other words, I・=I・₁ +I・₂ Therefore, the magnitude of the current I ₁ is |I・₁ |=(|I・| ² −|I・₂ | ² ) 1/2 ...(5) Become.

_The magnitude of the resistance value R _X of the resistor to be measured ₃ is R _X = _V
= V _L , so divide equation (4)′ by (5) and get R _X = V _L
The resistance value R _X can be found from ÷I ₁ .

[Problem that the invention attempts to solve]

This conventional device is convenient because it can measure resistance in the same manner as described above even for resistors on which no direct current is superimposed, and is widely used.

However, from the DC power supply 2 to the resistor to be measured 3
If the DC voltage generated across the capacitor C when a current is passed through it is, for example, V, then the capacitor C is charged via the input winding of the transformer T until it reaches the voltage V. Furthermore, the formula is given by the AC current _I2 for measurement.
Since the _alternating current voltage V _L (= _V

Therefore, for example, when one measurement is completed and the test probes 5 and 6 are separated from the resistor to be measured 3, there will be a voltage between the two poles of the capacitor C from V-V _L to V+V _L depending on the timing of the separation. A voltage of a certain value in the range remains, and when no direct current is applied, a voltage of a certain value in the range from −V _L to V _L remains. In this state, if you try to make the next measurement by touching the test probes 5 and 6 to other resistors to be measured, the measured value will become temporarily unstable due to the residual voltage, but the residual voltage will be canceled and stable measurements will be made. It takes time to obtain the value. For this reason, it is necessary to short-circuit the capacitor each time using a jumper wire or the like to discharge the residual voltage, which is troublesome for the user.

This invention was developed in view of the above points, and its purpose is to provide an easy-to-use resistance meter in which the residual voltage of the capacitor is automatically canceled each time a measurement is completed.

[Means for solving problems]

Referring to FIG. 1, which shows an embodiment of this invention, in order to solve the above-mentioned problems, the input side of the measuring section 20 is equipped with a short-circuit capacitor, which is operated by the drive current from the AC constant current source 10. relay 2
1 is provided, and the supply of this drive current is turned on and off in conjunction with bringing the test probe into contact with and separating from the resistor to be measured.

[Effect]

In this embodiment, for example, when the test probes 22, 23 are brought into contact with the resistor to be measured 3, the switching circuit 16 in the AC constant current source 10 is turned on, supplying drive current to the relay 21, and its contacts are opened. state. Test probes 22, 23
When the resistor 15 is separated from the resistor 3 to be measured, the comparator 15 is activated, and its output turns off the switching circuit 16, cutting off the supply of drive current. relay 2
1 self-returns to the closed state, and the capacitor C is short-circuited via the winding of the transformer T, so that its residual voltage is automatically canceled.

〔Example〕

This invention will be explained in detail below with reference to the embodiment shown in FIG. 1 above.

This resistance meter includes an AC constant current source 10 and a measuring section 20. A pair of signal supply test probes 22a and 23a are connected to the AC constant current source 10, and a pair of signal detecting probes are connected to the measuring section 20. Side test probes 22b and 23b are connected respectively. The AC constant current source 10 has a signal source of, for example, 1kHz.
An oscillator 11 is provided, and an automatic gain controller 12 is provided to make the output an alternating current voltage signal at a constant level. A constant level voltage signal sent from the automatic gain controller 12 is applied to, for example, the next stage voltage/current converter 13, where it is converted into a constant current signal I for measurement, and is applied via a reference resistor R _S. The current is made to flow through the measuring resistor 3. In this case, in order to keep the constant current signal I sent from the voltage/current converter 13 at a constant level, the reference resistor
An error amplifier 14 is provided to monitor the voltage across R _S , and its output controls the operation of the voltage/current converter 13. Note that depending on the resistor to be measured 3, an external DC power supply 2 may be used.
There may be cases where no direct current is passed through the sensor, but there is no change in the method of measurement.

In this embodiment, for example, a comparator 15 monitors the current output terminal voltage in the voltage/current converter 13, and a switching circuit 16 turns on and off the drive current supplied to the relay 21 based on the output of the comparator 15. is provided. That is, the signal supply side test probe 22
When a certain level of measurement current is flowing through the resistor to be measured 3 through a and 23a, the above voltage /
A predetermined voltage is generated at the current output terminal in the current converter 13, but when the signal supply side test probes 22a, 23a are separated from the resistor under test 3 after measurement, the measurement current stops flowing, so the above current The voltage at the output terminal rises and becomes what is called an open circuit voltage. Therefore, if a voltage slightly higher than the current output terminal voltage when the measurement current is flowing is applied to the comparator 15 as a reference voltage, it is possible to distinguish between measurement and non-measurement. In this embodiment, for example, during measurement, the output of the comparator 15 is off and the switching circuit 16 is on. Drive current is supplied, and when not measuring, comparator 15
The switching circuit 16 is turned off by the output from the switching circuit 16, and the supply of drive current is cut off.

The measurement unit 20 is connected to signal supply side test probes 22b and 23b, similarly to the conventional device described above. A DC blocking capacitor C and an isolation transformer T are provided at the input section, and a voltage V _L of the same magnitude as the voltage V _X generated by the current I ₁ shunted to the resistor 3 to be measured is For example, it is applied to an amplifier 24 via a transformer T. The output of this amplifier 24 is transmitted to the next stage detector 25.
The signal is detected and becomes a direct current, which is digitally converted by the A/D converter 26 and then input to the measurement circuit 27. In the measuring circuit 27, the current _I
The value of is determined, and this current value and the above voltage V _L (=
The resistance value R _X of the resistor to be measured 3 can be obtained by dividing the measured value of V _X ) by R _X =V _L ÷I ₁ .

In this embodiment, as described above, the relay 21 is provided on the input side of the measuring section 20 in parallel to the capacitor C, and when the drive current is supplied and the relay is turned on, it is indicated by a solid line. The contacts are then opened to take the desired measurement. For example, when the measurement is completed, the signal supply side test probe 22
When a and 23a are separated from the resistor to be measured 3, the supply of drive current is cut off and the relay 21 is turned off, and as shown by the dotted line, it returns to its original state and its contacts are closed, and the residual voltage of the capacitor C becomes Discharge automatically. As described above, the supply and disconnection of the drive current to the relay 21 are performed by the comparator 15 and the switching circuit 16 in the AC constant current source 10.

In this embodiment, one contact of the relay 21 is connected to one pole of the capacitor C, and the other contact is connected to the other pole of the capacitor C via the input winding of the transformer T. , this other contact may be directly connected to the other pole of the capacitor C. If there are no problems with leakage current during measurement or current capacity during discharge, replace the relay with an analog switch and turn it on.
It is also possible to voltage control the off operation.

〔effect〕

As explained in detail above, the ohmmeter according to this invention is equipped with a relay that shorts the DC blocking capacitor to discharge its residual voltage, and this relay connects the test probe to the resistance to be measured. The driving current is supplied in conjunction with contact with the body or separation from the resistor to be measured,
That supply is increasingly being cut off.

This eliminates the need for cumbersome manual work such as shorting the capacitors with a jumper wire or the like after each measurement, which can greatly contribute to improving measurement efficiency.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the resistance meter according to this invention, and FIG. 2 is a block diagram of a conventional device. In the figure, 2 is a DC power supply, 3 is a resistor to be measured, and 10
is an AC constant current source, 20 is a measuring section, 21 is a relay,
22 and 23 are test probes, and C is a capacitor.

Claims (1)

[Claims for Utility Model Registration] Includes a pair of signal supply side test probes connected to an AC constant current source, and a pair of signal detection side test probes having a DC blocking capacitor and connected to a measurement section, An AC constant current signal for measurement is applied to the resistor under test to which DC is applied via the signal supply side test probe, and a current signal flowing through the resistor under test and an AC voltage signal generated in the resistor under test are detected. In an ohmmeter that determines the resistance value of the resistor to be measured by detecting it with the signal detection side test probe and separating it from the direct current using the capacitor, the capacitor is selected between the pair of signal detection side test probes. a relay connected so as to cause a short-circuit condition; and a relay driving means for driving the relay by detecting contact and separation of the signal supply side test probe with respect to the resistor to be measured. The means opens the contacts of the relay to make the capacitor non-short-circuited when the signal supplying test probe is in contact with the resistor to be measured, and when the signal supplying test probe is separated from the resistor to be measured. A resistance meter characterized in that the contacts of the relay are closed to short-circuit the capacitor.