6.2
OXYGEN CELL REPLACEMENT
:
6.2.1 The oxygen cell, located within the sensor barrel, has a life expectancy of at least one
year. The cell is similar to a battery except unlike a battery, it produces a current which is
directly proportional to the level of oxygen it senses in a gaseous environment. In normal
air, the current generated by a live cell is approximately 0.8 milli-amperes, which
produces a conditioned reading on the display of 20.9% ±0.2. This current output is very
constant in normal air throughout the cell’s life. At end of life the output drops quickly
and reading in the air will suddenly drop below 20.9%. When the push button calibration
procedure given in Section 7.0 can no longer be performed, the cell must be replaced.
6.2.2 To replace the cell, unscrew the retaining cap and screen at the lower extremity of the
sensor barrel housing assembly. The cell housing can not be extracted by holding in a
vertical position. Unplug cell from its mating connector. Replace with fresh cell, making
sure to seat connector and mating plug securely before re-assembly into barrel housing.
Re-insert cell into the barrel, while slightly rotating the cell assembly. Replace screen and
retaining cap. Then follow procedure given for cell calibration in Section 7.0.
6.3
GAUGING TAPE REPLACEMENT
In case of damage, the gauging tape may be replaced by following the procedure below:
6.3.1 Remove the oxygen sensor assembly by unplugging it from the tape end.
6.3.2 Remove storage barrel by loosening cap nuts on the side of the tape wiper housing.
6.3.3 Remove the round vapor seal assembly on the top of the tape wiper housing by backing
off the Allen set screw which holds it in place.
6.3.4 Now place the tape wiper in the off position and remove the tape wiper housing by
unfastening the (4) machine screws in the front of mounting plate. Pull the wiper
assembly out.
6.3.5. Completely unreel the old tape assembly.
6.3.6 Remove the six machine screws from the hub cover and lay it to the side.
6.3.7 Remove the battery from the battery holder and unplug the battery cap.
6.3.8 Note that the end of the metallic tape inside the hub is grounded by a machine screw and
washer. The tefzel tape cover at this point has been trimmed away to permit good ground
contact. Also note that the tape’s outer conductors are spliced to two of the wires that
originated at circuit board. Notice the color of these wires so that when re-assembling, the
correct wire will be connected t the top and bottom tape conductor.
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