BT CGA-411 Operation Manual page 37

D. Replacement of the Oxygen Sensor
The oxygen cell should not be opened since it contains a corrosive electrolyte. The old
cell should be returned to Bascom-Turner for proper disposal. Please use the container furnished
with the replacement cell for the return.
The tool required for replacement is a Phillips #1 screwdriver. If the new sensor requires
adjustment, then a small implement wide enough to reach both push-button switches on the side
of the instrument is also required.
I. Replacement of the Oxygen Cell
1. Follow steps 1 through 3 for replacing the CO/H
from the instrument.
2. Locate the oxygen cell, a white cylinder about 1" in diameter resting against the side
of the gas manifold. Lift the clip that secures the cell against the manifold and
remove the cell.
3. Verify that an O-ring is in place at the sensor port. Place the new oxygen cell in
position with the screened opening against the O-ring. Slide the clip in place taking
care not to crimp or damage the electrical leads of the cell.
4. Reconnect the four connectors to the bottom of the board and return the main board
into place in the case by following instructions 6 through 8 for replacing the
CO/H S cell (Section 12C). Be sure to allow sufficient time for the CO cell to
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stabilize before autozeroing. After AUTO ZERO, place the selector switch at the %
Oxygen position and verify that the detector reads 20.9 ±0.1 % Oxygen.
II. Adjustment of the Oxygen Cell
Verify that the oxygen cell is working correctly by sampling low pressure (6"-7" of water)
system gas for about one minute. The detector should read 0.2 (or less) % Oxygen with the
selector switch at the % Oxygen display. If it does not, the detector must be adjusted as
described below.
Enter the manual calibration mode (see the beginning of this Section 12) and press switch
#2 until O2 appears on the display followed by 9999 (9 depressions of switch #2). Introduce low
pressure system gas, or pure methane, for at least 40 seconds. Press switch #1 to "flash" the first
digit of the display. Press switch #1 again to advance the first digit to 0 (zero). The display will
now read 0999 with the underlined digit flashing. Press switch #2 once to advance the display to
"Air", the beginning of the normal AUTO ZERO routine. Do not allow to autozero, but turn the
front panel switch to the % Oxygen position and verify that the reading is 0.2 or less. Remove
the system gas, allow the instrument to purge in air for at least 40 seconds, and AUTO ZERO. If
"nogo" appears during AUTO ZERO, use the coarse zero routine described in Section 6.
S cell and remove the main board
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