Multimeter to measure silicon controlled rectifier_how to measure the quality of silicon controlled rectifier
There are two types of thyristors: one-way thyristor and two-way thyristor, both of which have three electrodes. A one-way thyristor has a cathode (K), an anode (A), and a control electrode (G). The bidirectional thyristor is equivalent to two single thyristors connected in reverse parallel. That is, one of the unidirectional silicon anodes is connected to the other cathode, and its leading end is called T2 pole, and one of the unidirectional silicon cathodes is connected to the other anode, and its leading end is called T2 pole, and the rest are control poles. Pole (G).
1. Discrimination of unidirectional and bidirectional thyristors: firstly measure the two poles, if the positive and negative measurement pointers do not move (R×1 block), it may be A, K or G, A poles (for unidirectional thyristors) ) It may also be T2, T1 or T2, G pole (for triac). If one of the measurements indicates tens to hundreds of ohms, it must be a one-way 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 the positive and negative test indications are tens to hundreds of ohms, it must be a triac. Then turn the knob to R×1 or R×10 to retest, there must be one resistance value slightly larger, then the red pen connected to the slightly larger one is the G pole, the black pen is connected to the T1 pole, and the rest are T2 poles .
2. The difference in performance: Turn the knob to R×1 gear, for 1~6A unidirectional 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, and the black pen is not separated from the A pole. Disconnect the G pole, and the pointer should indicate tens 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 turn off the A pole momentarily and turn it on again, the pointer should return to the ∞ position, indicating that the SCR is good.
For 1~6A bidirectional thyristor, 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. The G pole should be disconnected under the premise of ensuring that the black pen does not separate from the T2 pole. The pointer should indicate tens to more than one hundred Europe (depending on the size of the thyristor current and different manufacturers). Then reverse the two pens, repeat the above steps to measure once, and the pointer indication is more than ten to tens of ohms larger than the previous time, indicating that the SCR is good, and the trigger voltage (or current) is small. If the G pole is turned off while the A pole or T2 pole is kept connected, the pointer immediately returns to the ∞ position, indicating that the trigger current of the thyristor is too large or damaged. It can be further measured according to the method in Figure 2. For the one-way thyristor, the light should be on when the switch K is closed, and the light should not go out when the K switch is turned off, otherwise the thyristor is damaged.
For bidirectional thyristor, close the switch K, the light should be on, turn off K, the light should not go out. Then reverse the battery, repeat the above steps, should be the same result, it is good. Otherwise, the device is damaged.
The bidirectional thyristor also has three poles, which control rice G, the first anode T1, and the second anode T2. Actually T1 and T2 are used interchangeably. The basic detection method of the symbol of the triac is shown in the figure above.
1. Polarity discrimination
Discrimination between T1 pole and G pole: Use the multimeter Rx10 to measure the forward and reverse resistances between the poles. If you find that the positive and negative resistances between certain two poles are very small (about 150ll), then this The two poles are T1 and G poles. Then set the multimeter to the 'f-Rx1 gear, and measure the reverse resistance of these two poles in turn. The black test pen with the smaller resistance value is connected to the T1 pole, the other is the control pole C, and the rest is T2. pole. Take} bidirectional thyristor is MAC97A6/M329 model, measured with MF47F multimeter. If the measured resistance value is different when Rx100 is used (around 500ll), attention should be paid. If you measure a high-power thyristor, the data will be different, and the small current cannot be triggered, and the multimeter needs to be connected with an external (series) voltage to proceed.
2. Distinguishing between good and bad and continuity
Put the multimeter in the Rxlk block and measure the resistance between T1 and T2, G and T1. If the resistance is small, it means that the SCR has broken down. If the measured positive and negative resistances of G and T2 poles are very large (normally should be around hundreds of ohms). It means that the circuit has been disconnected.
To judge the conduction ability 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 supply (you can also replace it with another multimeter Rx1), then the hands of the meter are in the conduction state, and the dry battery is still in the conduction state, which is the conduction function for judging T1 to T2. The principle is very simple. Connect the positive pole of the battery to T1 to form a trigger voltage for the negative pole of the G fake dry battery. The current path is: from dry battery ten-T1 to G-thousand battery, the current path is triggered. At this time, the multimeter is also used as a power supply. Use, + in the negative pen - T1 - T2 - one in the positive pen, forming a path from T1 to T2.
The conduction performance from T2 to T1 is opposite to this polarity, and the town uses the same method to judge.
Experience shows that the gears of the multimeters used for different types of thyristors are different, and the measured resistance values are also different. For example, when it is difficult to find a small resistance value with Rx100 block, it is easy to find it with Rx10 block. SCR models are different, and the measured resistance values are quite different. For example, when measuring the one-way thyristor MCR100, only a small resistance value can be measured with the resistance range Rx1—R×1k of the multimeter in turn (no The second larger resistance value); For example, when measuring the one-way thyristor FD315M, when measuring with positive and negative test leads in turn, there are two resistance values when measuring with Rx100 or RXlk, but it is not easy to find which is smaller , If you use Rx1 or Rx10 to measure, it is easier to find a small resistance value. It is easy to find the G pole with the black test pen, and the K pole with the red test pen, so you must not be rigid.
