Maintenance and Troubleshooting | 6-17
General Troubleshooting
Your system may pass calibrations yet still seem to be reading incorrect
oxygen levels. If this is the case, check the following.
Leak Check
Leaks can lead to inaccurate readings especially if operating under a sig-
nificant pressure or vacuum. Check that all compression fitting and pipe
thread connections are leak tight.
You can check for leaks by sniffing the fittings with another gas. Use a
piece of tygon or plastic tubing with a 1/8” stainless steel nozzle to apply
the gas from a cylinder. Using stainless steel prevents any problems that
might occur with plastic melting the nozzle on hot sensor components.
To do this, connect a vacuum pump to the outlet of the sensor (should be
between 3 and 5 psi) and apply a low calibration gas (we recommend a
low PPM gas for the best results) to the inlet of the sensor. This pulls the
low calibration gas into the sensor. Allow the gas to stabilize and then
measure the cell millivolts. Spray 100% oxygen over the sample inlet
plumbing and when the cell millivolt decrease, it indicates a leak in that
area of the plumbing (a vacuum of the process pulls in the gas). If not con-
venient to view the control unit display, you can also apply a volt meter to
terminals 1 and 2 on the sensor board (Cell + and Cell -) to see if the cell
millivolrs change, indicating a leak.
If you want, you can also remove the sensor form the process (after al-
lowing the sensor to cool) and pressurize it with 5 lb. of air, plugging any
existing ports, the inlet probe and exhaust tube holes. Then go over the
sensor fitting with a leak detector fluid. If you see bubbles it indicates a
leak. If using this method, be sure to prevent the liquid from reaching the
furnace. If the furnace does get wet, allow it sufficient time to thoroughly
dry.
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