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34 MAY 2014 | FUEL OIL NEWS | www.fueloilnews.com By GeorGe Lanthier* testing Gas thermocouples The Testing of DC Milli-Voltage Is Important When Analyzing a Potential Problem HVAC/ HYDRONICS T his article is based on another of our Firedragon Field Notes that you can find on our website at www.FiredragonEnt.com The Field Note is taken from my book 'WIRING & Fuel Burning Equipment - Volume Two - Meters' © . The subject for this article is our #GA1 gas valve thermo- couple adapter. The adapter is used for testing gas valve pow- ered thermocouples. The GA1 has 11/32" U.S. threads, is gold plated for highly accurate readings and is used for gas valves both old and new and is exclusive to us. To perform these tests a multimeter such as our 81B, 88E or DM3218 must be used. Don't be confused by the figure numbers, it's because we're quoting the book and it's a legal thing. The testing of DC milli-voltage is important when ana- lyzing a potential problem with a standing gas pilot system. By using the meter on the mV scale we can determine if the heat from the pilot flame is working with the thermocouple generator to produce power to run our control system. The three tests we will examine are the open circuit test, Figure 3-7, the closed circuit test, Figure 3-8, and the drop out test. In Figure 3-7 we show a meter being used while perform- ing an open circuit test. The procedure for completing this test is as follows: • Turn the gas valve to the 'OFF' position. • Remove the thermocouple from the gas valve connection. • Connect the meter by clips to the thermocouple line and set the meter to read DC milli-volts (mVDC). Make sure the leads are in the proper terminals. Connect the black lead using the alligator clip to the end ball or contact portion of the thermocouple, and the red lead with an alligator clip to the copper portion of the thermocouple. • Set the gas valve to the 'PILOT' position. • Press the control knob down and light the gas pilot and observe the pilot flame. It should be set to the manufacturer's recommendations. • Take the reading, normally between 20 and 30 mVdc indicates a good thermocouple voltage or as required by the manufacturer. In Figure 3-8 we show a meter being used while performing a closed circuit test. The procedure for complet- ing this test is as fol- lows: • Turn the gas valve to the 'OFF' position. • Remove the thermocouple from the gas valve connection. • Turn the gas valve to the 'OFF' position. • Remove the ther mocouple from the gas valve connec tion and install a GA1 thermocouple test adapter, Figure 3-9. Connect the meter by clips to the thermocouple line and set the meter to read DC milli-volts (mVdc). Make sure the leads are in the proper terminals. Connect the black lead using an alligator clip to the set screw of the adapter, and the red lead using the alligator clip to the copper portion of the therm\couple. • Set the gas valve to the 'PILOT' position. • Press the control knob down and light the gas pilot and observe the pilot flame. It should be set to the manufacturer's recommendations. • Take the reading, normally between 10 and 15 mVdc indicates a good thermocouple voltage or as required by the manufacturer. In Figure 3-10 we show a meter being used while performing a drop out test. The pro- cedure for completing this test is as follows: Figure 3-7 Figure 3-8 Figure 3-10