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11.
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 access 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 pan head #4-40 black screw (see Figure 3) from
the right side of the instrument (as you face it) using a Phillips screwdriver and access a push-
button switch with a short rod 3/32" (or less) in diameter. Place the instrument on a flat surface
with some stop to keep the instrument in place. Set the front panel switch to the position nearest
AUTO ZERO and press both the push-button and RESET simultaneously. With both switches
depressed, turn the front panel switch to AUTO ZERO and release buttons. The instrument will
enter the set-up mode for manual calibration and adjust; the display will show
"Pu"
(pump).
The parameters that can be accessed in the set-up mode are described in Table 2. Each
state is reached sequentially by pressing the push-button and can be adjusted by using RESET
and the push-button in the same way as described in detail for setting alarm levels (see Section
10). 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,
"nogo"
will
appear during auto calibration. The sensor must then be calibrated manually.
To calibrate, enter the set-up mode (see above) and press the push-button 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 the RESET and the push-button, as described in Section 10 and in the example
below, until the display reads 2.50.
Example:
The display reads 1.45 with calibration gas. To adjust, press RESET. The
display will flash the left most digit, a zero. Press the push-button. The display will now flash
the second digit, 1. Press RESET to advance to 2; press the push-button. The third digit, 4, will
now be flashing. Press the RESET to advance the third digit to 5. Press the push-button; the last
digit, 5, will now be flashing. Press RESET until this digit is zero, and then press the push-
button. 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 RESET) to
adjust again to 2.50.
The procedure for calibrating manually the CO sensor is similar. After entering the set-
up mode, the push-button 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 RESET and the push-button as described in Section 10.
