How to test SCR using Multimeter

This post will discuss about testing SCR – Silicon Controlled Rectifier with thte help of Ohmmeter.

The thyristor pin assignment  diagram of TO-220 package is given for ready reference.

Identify the terminals of the Ohmmeter:

• Using a junction diode, we can find out which ohmmeter lead is positive and which is negative.
• Connect the general purpose PN junction diode to across the positive and negative terminals of the Ohmmeter.
• The ohmmeter will indicate continuity only when the positive lead is connected to the anode of the diode and the negative lead is connected to the cathode.
• The SCR can be tested with an ohmmeter based on this concept.

Procedure to Test the SCR with the help of Ohmmeter:

• To test the SCR, connect the positive output lead of the ohmmeter to the anode and the negative lead to the cathode.
• The ohmmeter should indicate no continuity.
• Touch the gate of the SCR to the anode.
• The ohmmeter should indicate continuity through the SCR.
• When the gate lead is removed from the anode, conduction may stop or continue depending on whether the ohmmeter is supplying enough current to keep the device above its holding current level.
• If the ohmmeter indicates continuity through the SCR before the gate is touched to the anode, it indicates that the SCR is shorted.
• If the ohmmeter will not indicate continuity through the SCR after the gate has been touched to the anode, it indicates that the SCR is open.