How to measure the quality of thyristor with multimeter
There are two types of thyristors: unidirectional thyristors and bidirectional thyristors, both of which have three electrodes. Unidirectional thyristors have a cathode (K), an anode (A), and a control electrode (G). A bidirectional thyristor is equivalent to two single-phase thyristors connected in reverse parallel. One unidirectional silicon anode is connected to the other cathode, and its lead end is called T2 pole. One unidirectional silicon cathode is connected to the other anode, and its lead end is called T2 pole. The rest is the control pole (G).
1. Discrimination between single and bidirectional thyristors: First, measure both poles. If the forward and reverse pointers do not move (R × 1 gear), it may be A, K or G, A pole (for unidirectional thyristors) or T2, T1 or T2, G pole (for bidirectional thyristors). If one of the measurements indicates tens to hundreds of ohms, it must be a unidirectional thyristor. And the red pen is connected to the K pole, the black pen is connected to the G pole, and the rest is the A pole. If both the forward and reverse test indications are tens to hundreds of ohms, it must be a bidirectional thyristor. Turn the knob to R × 1 or R × 10 and retest. If there is a slightly larger resistance value, connect the red pen to the G pole, connect the black pen to the T1 pole, and connect the remaining to the T2 pole.
2. Performance difference: Turn the knob to R × 1 gear. For 1-6A unidirectional thyristors, connect the red pen to the K pole and the black pen to both the G and A poles. While keeping the black pen in the A pole state, disconnect the G pole. The pointer should indicate several tens of ohms to one hundred ohms. At this point, the thyristor has been triggered and the triggering voltage (or current) is low. Then instantly disconnect the A pole and reconnect it. If the pointer should return to the ∞ position, it indicates that the thyristor is in good condition.
For 1-6A bidirectional thyristors, connect the red pen to the T1 pole and the black pen to both the G and T2 poles. Disconnect the G pole while ensuring that the black pen does not detach from the T2 pole. The pointer should indicate several tens to over a hundred ohms (depending on the thyristor current and manufacturer). Then swap the two pens and repeat the above steps to measure once. If the pointer reading is slightly larger than the previous time by more than ten to tens of ohms, it indicates that the thyristor is good and the trigger voltage (or current) is small. If the G pole is disconnected while keeping the A or T2 pole connected, and the pointer immediately returns to the ∞ position, it indicates that the thyristor trigger current is too high or damaged. Further measurement can be carried out using the method shown in Figure 2. For a unidirectional thyristor, when the switch K is closed, the light should light up, and when the switch K is disconnected, the light should still not turn off. Otherwise, it indicates that the thyristor is damaged.
For bidirectional thyristors, when switch K is closed, the light should light up, and when switch K is disconnected, the light should not go out. Then reverse the battery and repeat the above steps. The same result should be obtained to indicate that it is good. Otherwise, it indicates that the device has been damaged.
