Panametrics CGA 351, User Manual, Page: 87 / 119

CGA 351 User’s Manual 81
Chapter 5.
Replacing the Thermocouple
The thermocouple is mounted on the bottom of the sensor furnace and extends approximately 2–3 in. into the sensor
furnace.
Note: For information regarding component locations and/or wiring connections in an optional enclosure, see
Appendix C.
CAUTION!
To prevent damage, the oxygen sensor must cool for about two hours after the unit is powered down
before the sensor enclosure door may be opened. Then, replace the thermocouple and reconnect the
power as quickly as possible to prevent corrosion of the analyzer components due to acid
condensation.
IMPORTANT:
These symbols indicate Caution - dangerously hot surfaces and risk of electric shock, respectively:
A standard screwdriver is the only tool needed for replacement of the thermocouple. Complete the following steps, in
the order shown, to remove the defective thermocouple:
1. Disconnect the main power to the CGA 351.
WARNING!
Failure to cut the main power at the external
disconnect device before proceeding will result in
serious personal injury.
2. Open the cover on the sensor and electronics enclosures.
WARNING!
The sensor furnace may still be hot. Always use
heat-resistant gloves when handling it.
3. Remove the oxygen sensor/manifold assembly, as described in the previous section.
4. Disconnect the thermocouple leads from TB2 in the electronics enclosure (make a note of the terminal pins for
each lead), and pull the leads through the conduit and into the sensor enclosure.
5. Remove the screw that secures the integral thermocouple clamp to the bottom of the sensor furnace.
Replacing the Thermocouple (cont.)
6. Extract the thermocouple from the sensor furnace, through the opening in the bottom of the sensor enclosure.
Install the new thermocouple by completing the following steps:
1. Insert the new thermocouple into the sensor furnace, being careful not to strike it against the heating element or
the pipe wall inside the sensor furnace.
2. Secure the thermocouple clamp to the bottom of the sensor furnace with the screw previously removed.
3. Route the thermocouple wires through the conduit and into the electronics enclosure.
4. Connect the thermocouple wire leads to the same pins from which the old leads were removed. The positive
(yellow) and negative (red) leads must be connected with the correct polarity.
5. Reinstall the oxygen sensor/manifold assembly into the bottom of the sensor enclosure and install the upper and
lower oxygen sensor clips, as described in the previous section.
6. Close the covers on both enclosures.
7. Energize the main power to the meter and calibrate the oxygen sensor (see “Calibrating the CGA 351” on
page 62).
This completes the replacement of the thermocouple.
Replacing the Sensor Furnace
The sensor furnace, which maintains the oxygen sensor at a stable operating temperature, is located in the sensor
enclosure and is easily replaceable. The following tools are required:
•
screwdriver