Multimeter for measurement of thyristors
There are two types of thyristors: one-way thyristors and two-way thyristors, both of which have three electrodes. One-way thyristor has cathode (K), anode (A), and control electrode (G). A two-way thyristor is equivalent to two single-phase thyristors connected in reverse parallel. That is, 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. The rest is the control Pole (G).
1. Distinguish between unidirectional and bidirectional thyristors: first test two poles, if the forward and reverse measurement pointers do not move (R×1 block), it may be A, K or G, A pole (for unidirectional thyristors ) may also be T2, T1 or T2, G pole (for a two-way thyristor). If one of the measurement indications is tens to hundreds of ohms, it must be a unidirectional thyristor. 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 the forward and reverse test indications are tens to hundreds of ohms, it must be a bidirectional thyristor. Then turn the knob to R×1 or R×10 and retest. There must be one resistance value that is slightly larger. The larger one is connected to the red pen as the G pole, the black pen is connected to the T1 pole, and the remaining one is the T2 pole. .
2. Difference in performance: Turn the knob to R×1 gear. For 1~6A one-way thyristor, the red pen is connected to the K pole, and the black pen is connected to the G and A poles at the same time. Keep the black pen from leaving the A pole state. Disconnect the G pole, and the pointer should indicate dozens of ohms to one hundred ohms. At this time, the thyristor has been triggered, and the trigger voltage is low (or the trigger current is small). Then momentarily disconnect the A pole and then connect it again. The pointer should return to the ∞ position, indicating that the thyristor is good.
For 1~6A triac, the red pen is connected to the T1 pole, and the black pen is connected to the G and T2 poles at the same time. Disconnect the G pole while ensuring that the black pen does not break away from the T2 pole. The pointer should indicate tens to more than one hundred. ohms (depending on the current size of the thyristor and different manufacturers). Then swap the two pens and repeat the above steps to measure once. If the pointer indication is slightly larger than the last time by more than ten to dozens 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 pole or T2 pole connected, and the pointer immediately returns to the ∞ position, it means that the trigger current of the thyristor is too large or damaged. Further measurement can be made according to the method in Figure 2. For one-way thyristor, when switch K is closed, the light should be on, and when K is turned off, the light still remains on, otherwise the thyristor is damaged.
For a two-way thyristor, when switch K is closed, the light should light up, and when K is turned off, the light should not go out. Then reverse the battery connection and repeat the above steps. If the result is the same, it means it is good. Otherwise, the device is damaged.
The two-way thyristor also has three poles, which control rice G, the first anode T1, and the second anode T2. In fact, T1 and T2 are used interchangeably. The basic detection method of the symbol of a triac is shown in the figure above.
1. Polarity discrimination
Distinguish between T1 pole and G pole: Use Rx10 block of multimeter to measure the positive and reverse resistance between each pole respectively. If it is found that the positive and reverse anode resistance between two poles are very small (about 150ll), then this The two poles are T1 and G pole. Then set the multimeter to 'f-Rx1', and measure the reverse resistance of these two poles in turn. The black test lead with the smaller resistance measured is connected to the T1 pole, the other is the control pole C, and the remaining is T2. pole. The bidirectional thyristor is model MAC97A6/M329, measured with MF47F multimeter. If the measured resistance value is different when using Rx100 block (around 500ll), please pay attention. If you measure high-power thyristors, the data will be different. Small currents cannot be triggered, and the multimeter needs to apply an external (series) voltage.
2. Distinguish the quality and continuity
You can put the multimeter in the Rxlk block and measure the resistance between T1 and T2, G and T1. If the resistance is very small, it means that the thyristor has broken down. If the measured forward and reverse resistance values of G and T2 poles are both very large (normally they should be around several hundred ohms). It means the circuit is broken.
To determine the conductivity of the thyristor, connect the black test lead of the multimeter to the T1 pole and the red test lead to the T2 pole. Use a dry battery as the trigger power source (you can also use another multimeter Rx1 instead). At this time, the hands of the meter are in a conductive state, and the dry battery is still in a conductive state after being separated. This is the conductive function for judging T1 to T2. The principle is very simple. The positive electrode of the battery is connected to T1, and a trigger voltage is formed on the negative electrode of the G fake dry battery. The current path is: from the dry battery ten to T1 to the G thousand battery. The current path is formed and is triggered. At this time, the multimeter also serves as a power supply. Use, +-T1-T2 in the negative test lead and +-T2 in the positive test lead to form a path from T1 to T2.
