T
ROUBLESHOOTING
748250-L Rosemount Analytical October 1999
5-3
Model 880A Non-Dispersive Infrared Analyzer
5.2 VOLTAGE CHECKS
Refer to Section 3.7 and ensure that the voltages for the detector signal and the three
power supplies are correct.
5.3 OSCILLATOR TUNE ADJUSTMENT
This procedure should not be performed on a routine basis:
1. Refer to Section 3.7, and access the Oscillator Tune display.
2. Refer to Figure 3-1. Adjust coil knob (Oscillator Tune, located on top of the
detector housing) until a maximum reading is obtained on the display.
3. Adjust the coil
counterclockwise
until the unit reads between 75 and 80% of the
maximum value.
5.4 PREAMP GAIN
The preamp gain is used to adjust the fullscale value at TP2 and the diagnostic
display to 7.5V. To prevent saturation, this value must never be higher than 7.5V,
fullscale. If this value is too low or is above 7.5V, adjust the preamp gain.
1. Refer to Section 3.7, and access the Detector Signal display.
2. Flow SPAN calibration gas for the least sensitive range through the SAMPLE CELL
until display reading stabilizes.
An example:
Range 1 - 500 ppm CO
Range 2 - 2000 ppm CO
Range 3 - 5000 ppm CO
In this case, the least sensitive range would be 5000 ppm.
If the calibration gas is not equal to fullscale, find the percent fullscale of the
calibration gas by looking at the application curve at the back of the manual.
Multiply this value by 7.5 and record the resultant value for Step 5. For example, if
the SPAN gas is 67 % of fullscale, then
(0.67)(7.5)= 5
In this case, the value to be used in Step 5 is 5.
3. Refer to Figure 3-1. Adjust the displayed value with preamplifier gain
potentiometer R3, located on the Signal Board, for the value obtained in Step 4.
THIS VALUE SHOULD NEVER BE HIGHER THAN 7.5.
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