How to use a multimeter to measure the polarity of a thyristor
1. Polarity discrimination
Discrimination between T1 and G poles: Use a multimeter Rx10 to measure the positive and negative resistance between each pole. If it is found that the positive and negative resistance between two poles is very small (about 150ll), then these two poles are T1 and G poles. Then set the multimeter to the 'f-Rx1' position and measure the reverse resistance of these two poles alternately. Connect the black probe with the smaller resistance to the T1 pole, the other to the control pole C, and the remaining to the T2 pole. The bidirectional thyristor is the MAC97A6/M329 model, measured with an MF47F multimeter. If the resistance value measured when using Rx100 gear is different (around 500ll), attention should be paid. If measuring high-power thyristors, the data will be different. Small currents cannot be triggered, and a multimeter requires an external (series) voltage to be used.
2. Distinguish between good and bad and conductivity
Can the multimeter be placed in the Rxlk position 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 very high (normally around several hundred ohms), it indicates that the circuit has been broken.
To determine the conductivity of the thyristor, connect the black probe of the multimeter to the T1 pole and the red probe to the T2 pole. Using a dry battery as the trigger power source (or using another multimeter Rx1 as a substitute), the hands of the meter will be in a conductive state, and the dry battery will still be in a conductive state after leaving. This is the ability of the conductive component to distinguish between T1 and T2. The principle is very simple. Connect T1 to the positive pole of the battery, and a trigger voltage is formed on the negative pole of the G fake dry battery. The current path is: from the dry battery ten T1 to one thousand G batteries, a current path is formed and triggered. At this time, the multimeter also serves as a power source. The negative probe+- T1- T2 and the positive probe+- T2 form a path from T1 to T2.
The conductivity performance from T2 to T1 is opposite in polarity, and the same method is used for discrimination.
Experience has shown that different models of thyristors use multimeters with different gear positions, and the measured resistance values are also different. For example, when using the Rx100 gear, it is difficult to detect smaller resistance values, but switching to the Rx10 gear makes it easier to detect. The measured resistance values vary greatly depending on the type of thyristor. For example, when measuring the unidirectional thyristor MCR100, using the resistance range Rx1-R × 1k of the multimeter to measure alternately can only result in one smaller resistance value (without a second larger resistance value); For example, when measuring the unidirectional thyristor FD315M, when using positive and negative probes alternately, there are two resistance values when using Rx100 or RXlk for measurement, but it is not easy to find which one is smaller. If using Rx1 or Rx10 gear for measurement, it is easier to find the smaller resistance value. Use a black probe to determine the G pole and a red probe to determine the K pole, which is easier to find. Therefore, it is important not to use a rigid sleeve.
