How to use a digital multimeter to measure a solid state relay
Solid State Relay is abbreviated as SSR. it is a new type of non-contact switch composed of electronic components with reliable operation, fast switching speed and long life, replacing conventional relays in control circuits.
Solid state relay is a four-terminal device
Two of the INPUT terminals for the input, connected to the control signal, the other two terminals for the output, connected to the relay. Solid state relays can be classified into DC and AC solid state relays according to the type of load, with power transistors as the switching element in the former and bi-directional SCRs as the switching element in the latter.
AC over-zero type solid state relay principle. The so-called over-zero refers to the AC voltage is zero or just above zero when triggering the SCR, so as to reduce the impact on the power supply when the SCR conducts. Generally the zero crossing voltage is defined as ± 25V, in this region as long as the input signal, SSR on, when the power supply voltage is greater than ± 25V, plus the input signal SSR does not immediately on, only until the power supply down to the next zero crossing region, SSR on.
Detection of SSR can be measured at its input with or without DC voltage, DC voltage that the input signal is normal, and then measure the output with or without AC voltage. If there is, that SSR is normal, such as no or very low voltage drop, indicating that the solid state relay is damaged!
Use the digital multimeter diode gear, ①, ②, ③, ④ for forward and reverse measurement of the test data can be seen, when the red pen connected to the ① foot, the black pen connected to the ② foot, the meter shows the value of 1381 (1.381V), the exchange of the pen to measure the meter displays the overflow symbol "1"; when the red pen connected to the ④ foot, the black pen connected to the ③ time When the red pen is connected to pin ④, the black pen is connected to ③, the instrument shows the value of 543 (0.543V), exchange pen measurement, the instrument shows the overflow symbol "1"; in the rest of the several test states, the instrument shows the overflow symbol "1". It is not difficult to conclude that: ①, ② feet for the DC input of the device under test, ① feet for the positive pole, ② feet for the negative pole, "1.381V" is the solid-state relay internal light-emitting diode positive voltage drop; ③, ④ feet for the DC output, ③ feet for the positive pole, ④ feet for the negative pole, "0.543V "0.543V" is the forward voltage drop of the protection diode connected in parallel at the output of the solid state relay. Note that, for the solid state relay without protection diode at the output, no matter how to exchange the meter pen to measure its ③ and ④ feet, the meter will display the overflow symbol "1". When using different models of digital multimeter to measure the internal light-emitting diode of the solid-state relay, some instruments show the value of the readings sometimes just flash out momentarily, and then show the overflow symbol "1", encountered in this case, you can repeatedly exchange pens to measure several times until the conclusion of the test!
