JPH0330829B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a contact resistance circuit using a four-terminal method, and its purpose is to reduce measurement errors.

Contact resistance measurement using the four-terminal method involves contacting two terminals connected through a contact with a current electrode that flows a constant current, and also contacting a voltage electrode with the same terminal to measure the voltage drop between the two terminals. The contact resistance of the current electrode is measured, but if the contact of the current electrode with the terminal is not proper and the resistance of the contact part is high, the constant current circuit will not operate properly and cause erroneous measurements. If the resistance of the contact portion is high, the voltage electrode will be in an electrically floating state, which may also cause erroneous measurements.

Therefore, in the four-terminal method, reducing the contact resistance of the electrodes as low as possible is the basis for preventing erroneous measurements, so this application takes into account that these contact resistances are below the allowable value. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention, which provide a highly accurate contact resistance measuring circuit, will be described below with reference to FIGS. 1 to 5.

Voltage electrodes 6 and 7 of current electrodes 4 and 5 are brought into contact with terminals 2 and 3 of an electrical switch 1, which is a contact point to be measured, such as a relay or a microswitch, respectively.

These electrodes 4, 5, 6, 7 are connected to changeover switches 12, 12, . . . operated by a control circuit 11, as shown in FIG. The current electrodes 4 and 5 are connected to a constant current circuit 8 via a changeover switch 12.
and are selectively connected to continuity determination circuits 13, 13. Further, the voltage electrodes 6 and 7 are selectively connected via a changeover switch 12 to a resistance measuring circuit for measuring the contact resistance R of the contacts. And continuity determination circuit 13,
The continuity judgment signal No. 13, the measured resistance signal of the resistance measuring circuit, and the state signal of the control circuit are connected to the pass/fail judgment circuit, and the continuity judgment signal and the measured resistance signal are input to the AND gate to perform the pass/fail judgment. It is set to output. Here, the resistance measuring circuit 9 compares the actual value of the contact contact resistance R with a preset value which is a resistance value serving as a judgment criterion set in advance.
It is also possible to convert the signal into a digital signal and input it to the pass/fail judgment circuit 10. A reference voltage is applied to the negative terminal of the comparator 14 shown in Figure 3 as the continuity determination circuit 13, and the positive terminal is connected to a resistor (10KΩ in the figure).
The detection end 12b is connected to the changeover switch 12 via. Here, the resistance r that provides the reference voltage is set to several ohms, but it varies depending on the surface treatment condition of the terminals of the electrical switch, the contact resistance value, the measurement accuracy, etc.

Next, regarding measurement, selector switch 12
are in contact with the constant current circuit side and the resistance measuring circuit side, and as shown in FIG.
5, the voltage drop is detected by the voltage electrodes 6 and 7, and the resistance measuring circuit 9 generates a digitized signal indicating whether the resistance is high or low relative to the set value.

Next, when the changeover switch 12 is switched between the continuity judgment circuit side and the ground side, the contact resistances rv and ri of the electrodes are inserted between the ground and the continuity judgment circuit 13 shown in Fig. 3, as shown in Fig. 5. Therefore, if the contact resistance rv,
When ri becomes larger than the resistance r, causing a measurement error, the positive terminal of the comparator 14 becomes a high potential, the comparator is inverted to H, and an error signal indicating the occurrence of an error is sent from the output terminal 13a to make a pass/fail judgment. It is input to the circuit 10 and measured so that the previously measured resistance value is regarded as a measurement value with a large error. If the contact resistances rv and ri are smaller than the resistance r, the pass/fail judgment circuit outputs to the outside that normal contact contact measurement work has been performed, or the contact resistance value is output to the outside by an external printer, other measuring circuit, or inspection. Transferred to the CPU along with the circuit. If the measured resistance value fails even if the measurement is normal, it is recorded or a failure indication is outputted to the pass/fail selection circuit of the electrical switch to the outside.

Of course, if the contact resistance during measurement is high, maintenance such as removing dirt from the surfaces of electrodes 4, 5, 6, and 7 and checking for breaks in the lead wires to the electrodes will be performed to ensure that normal measurements are always performed unattended. It will be done.

In addition, as an exception to this implementation, the changeover switch and control circuit 1
1 may be replaced with an electromagnetic relay or may be made into a semiconductor. Further, the comparison between the set value and the measured value of the contact resistance and the digital determination process may be included in either the resistance measurement circuit or the quality determination circuit. Furthermore, the state of the control circuit may be input to the pass/fail judgment circuit to improve the reliability of the judgment and to enable more automatic measurement.

As explained above, according to the present invention, four terminals are formed by separately abutting a pair of current electrodes 4, 5 and a pair of voltage electrodes 6, 7 between two terminals 2, 3 which are electrically connected through contacts. In the resistance measuring circuit according to the present invention, a constant current circuit 8 is connected to current electrodes 4 and 5, and a voltage drop between terminals 2 and 3 is detected by voltage electrodes 6 and 7 to measure contact contact resistance R. , a continuity determination circuit 13 for an electrode connected between a current electrode and a voltage electrode that are in contact with one terminal, and a quality determination circuit 10 that performs AND determination between the signal from the resistance measurement circuit 9 and the signal from the continuity determination circuit 13; The structure consists of a control circuit 11 that switches and connects the electrode that contacts the terminal to a resistance measurement circuit 9 and continuity determination circuits 13, 13, and the measurement is performed by also measuring the contact resistance of the electrode, which can cause errors. Accuracy is improved, and since the control circuit 11 switches between resistance measurement and contact state measurement, measurements can be made without changing the contact state with the terminal, leaving no room for error and efficient. I can do it.

Now that it has become possible to measure the contact resistance of electrical switches with high precision and continuously, it has become possible to directly connect the assembly process of relays, microswitches, etc., and to perform measurement work unattended. This results in improved efficiency.

[Brief explanation of drawings]

1 to 5 show embodiments of the present invention, with FIG. 1 being a front view, FIGS. 2 and 3 being circuit diagrams, and FIGS.
Figure 5 is an equivalent circuit diagram during measurement. 2, 3: terminal, 4, 5: current electrode, 6, 7: voltage electrode, 8: constant current circuit, 9: resistance measurement circuit, 1
0: Good/failure judgment circuit, 11: Control circuit, 13: Continuity judgment circuit, R: Contact resistance.

Claims (1)

[Claims] 1 In a four-terminal resistance measurement circuit consisting of a pair of current electrodes and a voltage electrode in contact with each other between two terminals that are electrically connected via contacts, a constant current circuit is connected to the current electrodes to measure the resistance between the terminals. a resistance measurement circuit that detects a voltage drop with a voltage electrode and measures contact resistance; a continuity determination circuit for an electrode connected between a current electrode and a voltage electrode that are in contact with one terminal; and a signal of the resistance measurement circuit. A resistance measuring circuit comprising: a pass/fail determining circuit that performs an AND determination with a signal from a continuity determining circuit; and a control circuit that switches and connects an electrode in contact with the terminal to the resistance measuring circuit and the continuity determining circuit.