Check the triggering ability of the thyristor

To make the thyristor conductive, the following conditions must be met:

Firstly, the thyristor is in a forward connection, with the anode connected to the positive pole of the power supply and the cathode connected to the negative pole of the power supply;

Secondly, a positive trigger signal VGT should be applied to the door.

Once the thyristor is turned on, the gate loses its control function, and the thyristor can only turn off when the anode voltage VA drops by a certain specified value or when a reverse voltage is applied.

Select the R × 1 (or R × 10) range for the multimeter. Due to the battery voltage in the table being only 1.5V lower than the normal VGT value (usually 2.5-4V), the thyristor will not be damaged. The measurement is carried out in two steps:

The first step is to disconnect switch S. At this point, the thyristor has not yet conducted, and the measured resistance value is high. The meter needle should stop at infinity. Then close the switch and connect the gate to the anode, causing the gate potential to rise. This is equivalent to adding a positive trigger signal, so the thyristor conducts and the resistance reading is several ohms to tens of ohms.

Step two, disconnect the switch again. If the reading remains unchanged, it proves that the quality of the thyristor is good.