Measuring controllable silicon with a multimeter
Thyristors are divided into two types: unidirectional thyristor and bidirectional thyristor, both of which have three electrodes. Unidirectional controllable silicon has a cathode (K), an anode (A), and a control electrode (G). Bidirectional thyristors are equivalent to two individual thyristors connected in reverse parallel. One of the unidirectional silicon anodes is connected to the other cathode, and its lead out end is called T2 pole. One of the unidirectional silicon cathodes is connected to the other anode, and its lead out end is called T2 pole, while the rest is the control pole (G).
1. Discrimination of single and bidirectional thyristors: First, measure either pole. If the forward and reverse measuring pointers are not moving (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 connected to the A pole. If the forward and reverse test instructions are both tens to hundreds of ohms, it must be a bidirectional thyristor. Turn the knob to R × 1 or R × 10 for retesting. If there must be a slightly higher resistance once, the slightly higher red pen is connected to the G pole, the black pen is connected to the T1 pole, and the remaining is connected to the T2 pole.
2. Performance difference: Turn the knob to the R × 1 position. For 1-6A unidirectional thyristors, connect the red pen to the K pole and the black pen to both G and A poles. While keeping the black pen in the A pole state, disconnect the G pole. The pointer should indicate tens to 100 ohms. At this point, the thyristors have been triggered and the triggering voltage (or triggering current) is low. Then momentarily disconnect the A pole and connect it again, and the pointer should return to the ∞ position, indicating 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. While ensuring that the black pen does not detach from the T2 pole, disconnect the G pole. The pointer should indicate several tens to over one hundred ohms (depending on the current of the thyristors and the manufacturer). Then swap the two strokes and repeat the above steps to measure once. If the pointer indicates slightly more than ten to tens of ohms than the previous one, it indicates that the thyristor is in good condition and the triggering voltage (or current) is small. If the G pole is disconnected while keeping the A or T2 poles connected, and the pointer immediately returns to the ∞ position, it indicates that the triggering current of the thyristor is too high or damaged. Further measurement can be carried out using the method shown in Figure 2. For unidirectional thyristors, when the switch K is closed, the light should be on, but when the switch K is turned off, the light should still remain on. Otherwise, it indicates that the thyristors are damaged.
For bidirectional thyristor, when the switch K is closed, the light should light up, and when the switch K is turned off, the light should remain on. Then reverse connect the battery and repeat the above steps, all of which should be the same result to indicate that it is good. Otherwise, it indicates that the device has been damaged.
Bidirectional controllable silicon also has three poles, which are controlled by Ij to connect with the first anode T1 and the second anode T2. In fact, T1 and T2 are interchangeable. The basic symbol detection method for bidirectional thyristor is shown in the above figure.
1. Polarity discrimination
Discrimination between T1 and G poles: Use a multimeter to measure the forward and reverse resistance between each pole in Rx10 gear. If it is found that the forward and reverse resistance between a certain two poles is very small (about 150ll), then these two poles are T1 and G poles. Then set the multimeter to f-Rx1 gear and rotate to measure the reverse resistance of these two poles. The black probe with the smaller resistance value is connected to T1 pole, the other is the control pole C, and the remaining T2 pole. The bidirectional thyristor is the MAC97A6/M329 model, measured using an MF47F multimeter. If the resistance value measured when using Rx100 gear is different (around 500ll), attention should be paid. If testing high-power thyristors, the data will be different. Small currents cannot be triggered, and a multimeter needs to be connected in series with an additional voltage to perform the test.
2. Distinguishing between good and bad and continuity
The multimeter can be placed in Rxlk gear to measure the resistance between T1 and T2, G and T1. If the resistance is very small, it indicates that the thyristor has broken down. If the measured positive and negative resistance values of G and T2 poles are both high (normally around a few hundred ohms), it indicates that the circuit has been disconnected.
