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12.
MANUAL CALIBRATION, SENSOR REPLACEMENT, PUMP ADJUSTMENT
Manual calibration is required if a sensor has drifted too far to be calibrated automatically
and sometimes when a sensor is replaced. Since the procedures described below accesses basic
operating parameters, safeguards have been built to ensure that the set-up mode is not entered
accidentally.
To access the set-up mode, remove the instrument from its carryall and take out the
elongated rubber plug on its side. Place the instrument on a flat surface with some stop to keep
the instrument in place.
switches #1 and #2 (see Figure 7) simultaneously with a small implement wide enough to reach
both switches.
While switches #1 and #2 are depressed, turn the frontpanel switch from the
% Oxygen position to AUTO ZERO. The instrument will enter the set-up mode for manual
calibration and adjustment; the display will show "Pu" (pump).
The parameters that can be accessed in the set-up mode are described in Table 5. Each
state is reached sequentially by pressing switch #2 and can be adjusted by using switches #1 and
#2 in the same way as described in detail for setting alarm levels (see Section 11). Ordinarily,
only some of the parameters need be adjusted during manual calibration or when installing a new
sensor. The main adjustments to an instrument in the field are described separately below.
A.
Manual Calibration
If the sensitivity of a sensor has drifted too far to be automatically adjusted, "no go" will
appear during autocalibration. The sensor must then be calibrated manually.
To calibrate, enter the set-up mode (see above) and press switch #2 until GAS 2 appears
on the display (4 depressions). If clean air is being pumped through the instrument, the display
should show 0.00 or -0.00. Introduce calibration gas (2.5% methane) and adjust the display by
using switch #1 and switch #2, as described in Section 11 and in the example below, until the
display reads 2.50.
Example: The display reads 1.45 with calibration gas. To adjust, press switch #1. The
display will flash the left most digit, a zero. Press switch #2. The display will now flash the
second digit, 1. Press switch #1 to advance to 2; press switch #2. The third digit, 4, will now be
flashing. Press switch #1 to advance the third digit to 5. Press switch #2; the last digit, 5, will
now be flashing. Press switch #1 until this digit is zero, and then press switch #2. The display
will show "GAS 2" followed by a number which ought to be 2.50. If this number is more than
2.52 or less than 2.48, repeat the procedure (beginning with switch #1) to adjust again to 2.50.
The procedure for calibrating manually the CO sensor is similar. After entering the set-
up mode, switch #2 is pressed until "CO" appears on the display followed by a number (7
depressions). The number is adjusted to 100 (assuming the calibration gas contains 100 ppm
CO) by using switches #1 and #2 as described in Section 11.
Set the front panel switch to the % Oxygen position and press both
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