Ametek Thermox CEM O2/TM, User Manual

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7-8 | Thermox CEM O2/TM
Furnace Replacement
To replace the furnace, do the following (see Figure 7-3):
1. Disconnect cell clips.
2. Remove the thermocouple from the furnace (see the Thermocouple
Replacement section in this chapter for help).
3. Disconnect the furnace leads from terminals R and S on the sensor
board.
4. Loosen the compression fitting on the underside of the cell housing
using two 11/16” wrenches, and loosen the smaller union fitting on the
convection loop return using a 13/16” wrench and an 11/16” wrench.
To prevent stripping threads on any of the fittings, loosen each in turn
at small increments - don’t completely loosen the one fitting and then
try to loosen the other fitting.
5. While holding the furnace in one hand, remove the convection loop
mounting clamp, being sure to save the mounting clamp and screws
for when you install the new furnace.
6. Gently pull the cell housing out of the furnace and remove the fur-
nace.
7. Slip the new furnace onto the cell housing and attach the cell housing
using the furnace mounting clamp.
8. Remount the cell housing (reverse the actions taken in step 4).
9. Reinstall the thermocouple (reverse the actions taken in step 2).
10. Using an ohm meter, check for short circuits of the heater coil to the
metal thermocouple sheath. The resistance should be infinite. If you
measure a short circuit, loosen the screw that secures the thermocou-
ple and relocate slightly until resistance is infinite. Check that neither
furnace lead is short circuited to the metal furnace cover.
11. Reattach cell clips.
12. Reattach furnace leads (reverse the actions taken in step 3). Polarity is
not important.
13. Calibrate the system.