How to Test TRIAC with Multimeter?

In this article, we shall discuss how to test TRIAC with a multimeter. The triac is one of the important devices in the power semiconductor devices family. The triac is widely used for controlling the AC voltage.

How to test TRIAC with Digital Multimeter OR using Ohmmeter?

The symbol of the triac is given below.

Introduction 

1. The TRIAC is 5 layer, 3 terminal Power semiconductor device.
2. It has a pair of phase-controlled SCRs connected in an inverse parallel manner on the same chip.
3. It is a bidirectional device, which means it can conduct current in both directions.

Step by step Procedure 

1. The below steps explains how to test triac with a multimeter.
2. Select the multimeter setting on resistance mode.
3. find out the polarity of the ohmmeter lead using P-N junction diode. When positive lead is connected to the anode and negative lead is connected to cathode shows continuity.
4.  The triac remains in its off state when the positive voltage is applied at MT1 and the negative voltage is applied at MT2 with gate current zero.
5. In a similar way,  the triac remains in its off state when the positive voltage is applied at MT₂ and the negative voltage is applied at MT₁ with gate current zero.
6.  In steps No. 3 &4 of triac testing, the ohmmeter should indicate no continuity through the triac. It means triac offers very high resistance.
7. In steps No. 3 &4 of triac testing, if the ohmmeter shows continuity through the triac. It means triac is short circuit and defective.
8.  Now, if the gate of the triac gets positive voltage the device turns on either MT1 is positive with respect to MT₂ or MT₂ is positive with respect to MT₁. This can be done by connecting the gate of triac to positive lead( It may be MT₁ or MT₂ terminal, depending on which terminal has positive voltage through ohmmeter. 
9. As per step No.8, the triac must turn on and must show very low resistance or continuity between MT₁ and MT₂. If triac shows continuity triac under test is OK.  
10. If triac does not turn on as per step 8, triac offers very high resistance and triac is defective.
11. By following above steps, we can test the Triac with multimeter.
    

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