How to use a digital multimeter to measure the quality of solid-state relays in the following way
Solid state relay is referred to as SSR. It is a new type of non-contact switch composed of electronic components. It has the characteristics of reliable operation, fast switching speed and long life. It can replace conventional relays in control circuits.
Two terminals of INPUT are input terminals, connected to control signals, and the other two terminals are output terminals, connected to relays. Solid-state relays can be divided into DC and AC solid-state relays according to load type. The former uses power transistors as switching elements, and the latter uses triacs as switching elements.
Principle of AC zero-crossing solid state relay. The so-called zero-crossing means that the thyristor is triggered when the AC voltage is zero or just crosses zero, which can reduce the impact on the power supply when the thyristor is turned on. Generally, the zero-crossing voltage is defined as ±25V. In this area, as long as the input signal is added, the SSR will be turned on. When the power supply voltage is greater than ±25V, the SSR will not be turned on immediately when the input signal is added. It will only wait until the power supply drops to the next crossing voltage. The SSR is only turned on when it is in the zero area.
When detecting the SSR, you can measure whether there is DC voltage at the input end. The presence of DC voltage indicates that the input signal is normal, and then measure whether there is AC voltage at the output end. If there is, it means the SSR is normal. If there is none or the voltage drop is very low, it means the solid state relay is damaged.
Use the diode setting of the digital multimeter to perform forward and reverse measurements on ①, ②, ③, and ④. According to the test data, when the red test lead is connected to pin ① and the black test lead is connected to pin ②, the meter displays a value of 1381 (1.381V). Exchange the test leads. During measurement, the meter displays the overflow symbol "1"; when the red test lead is connected to pin ④ and the black test lead is connected to pin ③, the meter displays a value of 543 (0.543V). When the test leads are exchanged for measurement, the meter displays the overflow symbol "1"; in the remaining In several test states, the instrument displays the overflow symbol "1". It is not difficult to draw the conclusion from this: ① and ② pins are the DC input terminals of the device under test, ① pin is the positive pole, ② pin is the negative pole, “1.381V” is the forward voltage drop of the light-emitting diode inside the solid-state relay; ③, ④ pins is the DC output terminal, pin ③ is the positive pole, pin ④ is the negative pole, "0.543V" is the forward voltage drop of the protection diode connected in parallel to the output terminal of the solid-state relay. Note that for solid-state relays without protection diodes at the output end, no matter how the test leads are exchanged to measure the ③ and ④ pins, the meter will display the overflow symbol "1". When using different types of digital multimeters to measure the internal light-emitting diodes of solid-state relays, the display value of some meters sometimes only flashes the reading momentarily, and then displays the overflow symbol "1". In this case, you can repeatedly exchange the test leads and test several times until the Draw test conclusions
