4
R
OUTINE
O
PERATION AND
T
HEORY
748250-L Rosemount Analytical October 1999
4-1
Model 880A Non-Dispersive Infrared Analyzer
4.1 ROUTINE OPERATION
First set the range for desired operating range: 1, 2, or 3. Then follow the steps for
zero and span (Sections 3.8 and 3.9). Next supply sample gas through the instrument.
The Model 880A will now automatically and continuously analyze the sample stream.
As a check of instrument performance, it is recommended that the operator keep a log
of the zero/span status (percentage of pot value).
4.2 RECOMMENDED CALIBRATION FREQUENCY
Maximum permissible interval between calibrations depends on the analytical
accuracy required and cannot, therefore, be specified. It is recommended initially that
the instrument be calibrated once every 24 hours and that this practice be continued
unless experience indicates that some other interval is more appropriate.
Readout accuracy is directly proportional to change in barometric pressure (i.e., a
change in cell pressure of 10 mm of mercury will result in a readout error of
approximately 1% of reading). Therefore, if barometric pressure changes significantly,
it is advisable to recheck the calibration against an upscale standard gas.
4.3 SHUTDOWN
The Model 880A will retain settings during prolonged shutdown. Recalibrate the
instrument upon restart.
4.4 DETECTION SYSTEM THEORY
As shown in Figure 1-1, infrared radiation is produced from two separate energy
sources. This radiation is interrupted by a chopper at 5 Hz. Depending on the
application, the radiation may then be optically filtered to reduce background
interference from other infrared-absorbing components.
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