JPH0157745B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an insulation resistance measuring circuit used for testing subscriber lines in telephone circuits.

(2) Background of the technology The circuit shown in Figure 1 is used as an insulation resistance measuring circuit for testing subscriber lines in telephone circuits. Lines A and B of the subscriber line to be measured are connected to terminals A and B at the left end in FIG. 1, respectively. Turn on relay contact d _r ,
The residual charge on the line under test is discharged to ground, and then relay contact d _r is turned off and contacts x _a ⁰ and x _a ¹ are turned on to accumulate charge on the line. Turn on relay contacts d _cp ⁰ and d _cp ¹ to transfer the charge on the line to the capacitor.
Turn off relays x _a ⁰ and x _a ¹ , relay contacts d _cs ⁰ ,
Turn on d _cs ¹ and d _cs ² , measure the voltage charged in the capacitor with detector 1, and judge whether the insulation is good or bad. The above explanation was made for the A line, but the B
The same can be done for lines by operating the selection relay.

(3) Prior Art and Problems The insulation resistance measuring circuit described above required a voltage of 150 volts, and this voltage was not normally used elsewhere in the switchboard, so it had the disadvantage of requiring a special power supply circuit. . Furthermore, since the detector uses a differential amplifier composed of transistors, resistors, etc., the number of parts is large, and the width of the differential amplifier's non-sensing region is approximately 800 millivolts, resulting in low accuracy.

(4) Purpose of the Invention In view of the problems of the conventional circuit described above, the purpose of the present invention is based on the idea of using an operational amplifier instead of a differential amplifier as a detector, which reduces the number of circuit components and improves insulation. The object of the present invention is to obtain a measuring circuit which has a narrow dead area width for resistance measurement values, and therefore has high accuracy.

(5) Structure of the invention In the present invention, the A or B line of the subscriber line
A selection relay connected to select a line, a measurement relay connected from a switching contact of the selection relay to one of the normally open contacts of the first contact group, and one of the normally open contacts of the first contact group of the measurement relay. an operational amplifier connected from a normally closed contact of said terminating relay to a non-inverting input via a resistor and a normally open contact of a second contact group of said measuring relay; B of the subscriber line; a grounding relay connected from the line to a normally open contact, and a terminating resistor connected between a switching contact of the grounding relay and a normally open contact of the terminating relay, the normally closed contact of the grounding relay being grounded; The switching contact of the grounding relay is connected to the negative side of the power supply through a normally open contact of the third contact group of the measuring relay, the positive side of the power supply having a predetermined time constant with the capacitance of the subscriber line. connected to the other normally open contact of the first contact group of the measuring relay via a resistor defined as such,
A certain voltage is applied to the inverting input of the operational amplifier, thereby providing an insulation resistance measuring circuit for outputting the suitability of the insulation resistance of the subscriber line at the output of the operational amplifier.

(6) Embodiment of the Invention A circuit diagram of an insulation resistance measuring circuit as an embodiment of the present invention is shown in FIG. In the figure, the A and B lines of the subscriber line are connected to terminals A and B, respectively, terminal A is connected to the normally closed contact of contact la of the selection relay, and terminal B is connected to the normally open contact of contact la of the selection relay. connected to. The switching contact of contact la of the selection relay is connected to two places, one is the terminal relay d _r
to the switching contact y1 of the measuring relay, and the other to the normally open contact y1 of the measuring relay.
is connected to the positive +24 volt terminal of the power supply via resistor 2. The normally closed contact of the termination relay contact d _r is connected to the non-inverting input of the operational amplifier 5 through a resistor and the normally open contact y3 of the measuring relay. The normally open contact of the terminal relay contact d _r is resistor 6
through the switching contact of the grounding relay contact lb, and through the normally open contact y2 of the measuring relay to the negative terminal E of the power supply. The normally closed contact of contact lb of the grounding relay is grounded, and the normally open contact of contact lb of the grounding relay is connected to terminal B. The inverting input of operational amplifier 5 has a reference voltage V _D (19.5 volts in this example) obtained by dividing the power supply voltage of 24 volts by resistor 3 and resistor 4.
is applied.

Next, the operation of the above-mentioned circuit will be explained using an A line to ground insulation resistance test as an example. First, relay contacts la, lb,
Turn off y1, y2, and y3 and turn on relay contact d _r to discharge residual charge for 180 milliseconds.
After this, turn off relay contact d _r , y1, y2 and y
3 is turned on, the AB line is charged, and the output of the operational amplifier 5 is detected after 800 milliseconds. In Figure 3,
A voltage change during insulation resistance measurement at the non-inverting input terminal of the operational amplifier 5 is shown. Curve 11 in the figure shows the case where the insulation resistance of the circuit under test is good;
2 indicates a case where the value is below the specified value. After 800 milliseconds, the charging voltage at the non-inverting input terminal of operational amplifier 5 becomes
The resistance value of the aforementioned resistor 2 is determined so that the quality of the insulation state can be determined depending on whether it is higher or lower than V _D. If the voltage at the non-inverting input terminal is higher than V _D , a positive voltage is output to the output terminal (OUT) of the operational amplifier, and if it is lower than V _D , O volt is output.

In the circuit of the above-described embodiment, the width of the dead region is about 10 millivolts, which is a significant improvement over the conventional circuit's width of about 800 millivolts. Furthermore, as can be seen by comparing Figures 1 and 2, the number of parts has also been significantly reduced. In addition,
The insulation resistance between the B line and the ground and the insulation resistance between the A line and the B line can be similarly measured by operating the contacts la and lb.

(7) Effects of the Invention According to the present invention, it is possible to obtain a highly accurate measurement circuit that has a small number of circuit components and a narrow dead region width of the insulation resistance measurement value.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional type of insulation resistance measuring circuit, Fig. 2 is a circuit diagram showing an insulation resistance measuring circuit as an embodiment of the present invention, and Fig. 3 shows the operation of the circuit in Fig. 2. It is a characteristic diagram for explaining. 1... Detector, 2, 3, 4... Resistor, 5... Operational amplifier, 6... Resistor, la, lb, d _r , y1, y2, y3...
relay contact.

Claims (1)

[Claims] 1. A selection relay connected to select line A or line B of the subscriber line, a measurement relay connected from the switching contact of the selection relay to one of the normally open contacts of the first contact group, a terminating relay connected from one of the normally open contacts of one contact group to the switching contact;
an operational amplifier connected from a normally closed contact of the terminating relay to a non-inverting input via a resistor and a normally open contact of a second group of contacts of the measuring relay; a ground connected from the B line of the subscriber line to a normally open contact; a relay, and a terminating resistor connected between a switching contact of the grounding relay and a normally open contact of the terminating relay, the normally closed contact of the grounding relay being grounded, and the switching contact of the grounding relay being connected to the measuring relay. is connected to the negative side of the power supply through a normally open contact of a third contact group, the positive side of which is measured through a resistor determined to have a predetermined time constant together with the capacitance of the subscriber line. Connected to the other normally open contact of the first contact group of the relay, a certain voltage is applied to the inverting input of the operational amplifier, thereby outputting the suitability of the insulation resistance of the subscriber line to the output of the operational amplifier. Insulation resistance measurement circuit.