DC relay and AC contactor main parameter test circuit

The test circuit of the relay's contact resistance, coil resistance, coil pull-in voltage and release voltage is as shown in the figure. (1) Measure the contact resistance of the relay contacts. Generally, the R×1 scale of the multimeter is used, as shown in Figure (a). The normally closed contact is 0 ohms when closed. To measure the contact resistance of the normally open contact, the relay armature must be pressed down to fully close the contacts. , the multimeter indicates 0 ohms; loosen the armature, and the resistance should be infinite (∞). (2) Measure the coil resistance. Still use the R×1 block of the multimeter, as shown in Figure (b). (3) Measure the DC relay pull-in and release voltage and current. Choose a 0~35V DC stabilized power supply, set the multimeter to 100mA DC, and connect it to the relay coil circuit, as shown in Figure (c). Adjust the voltage regulator knob of the regulated power supply to gradually increase the power supply voltage from low. When you hear the "click" of the armature pulling in, record the pull-in current and voltage values ​​(use another voltmeter); however, the pull-in voltage and current are not very fixed, you need to do it several times and take the average value. . Then adjust the voltage adjustment knob to reduce the voltage until a "click" sound is heard, which is the release voltage and current value of the relay. (4) Measure the pull-in and release voltage and current of the AC contactor and intermediate relay. As shown in Figure (d), after connecting the voltage regulator TA to the 220V power supply, turn the voltage regulating handwheel. The indication values ​​of ammeter A and voltmeter V gradually rise. When a "click" sound is heard and the contactor (or intermediate relay) is closed, the A value is the pull-in current value and the V value is the pull-in voltage value. Then turn the voltage regulating handwheel to reduce the voltage. When you hear the contactor release sound, the A meter indicates the release current, and the V meter indicates the release voltage value. If the AC contactor coil is 380V, two voltage regulators need to be connected in series to obtain a higher test voltage.