How should an SCR be tested with an ohmmeter?

Testing a Silicon Controlled Rectifier (SCR) with an ohmmeter requires understanding the device's operation and its terminal configuration. To properly test an SCR, it is essential to apply the correct voltage polarity while taking measurements across its terminals.

When the testing is performed with the positive lead connected to the anode and the negative lead connected to the cathode, and the gate is shorted to the anode, this allows the SCR to be turned on. In this configuration, the gate voltage is effectively applied, meaning that if the SCR is functioning correctly, it should show a low resistance reading. This indicates that the SCR is in the conducting state.

The gate terminal's role is to control the conduction of the SCR; when a small sufficient gate current is supplied (by shorting the gate to the anode during testing), it allows the SCR to conduct current from the anode to the cathode. This condition can then be measured with an ohmmeter, verifying that the SCR is capable of switching on.

Other configurations do not suitably activate the SCR for testing purposes or may not accurately reflect its operational state.