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4 Operations/Analysis Unit
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
period). In this case, nitrogen or dry air (typically-100OF dewpoint or 2ppm
water) can be used. Manually switch in the zero offset check from the
control unit to operate the zero solenoid flag (depending upon the application,
this may or may not simultaneously insert a zero flag into the light path;
indeed, 90% of the time it is not needed). The factory zero offset value
was set from its best determined factory calibration and was approximately
set between 10-20% of the full scale range for the zero. After the field on-
line calibration, a zero offset value around a 10-20% meter range should be
set, using the potentiometer adjustment located within the analyzer control
unit to bring it into the 10-20% range. This may require a short term
area declassification (on explosion proof units) in order to make this adjust-
ment.
The zero offset adjustment potentiometer is panel-mount located
within the control unit. The potentiometer identified (zero- offset) is
adjusted while the reproducible zero fluid background is in the sample
cell. (This zero check may be automatically or manually operated
depending upon the sample system and electronic instrument design).
RECORD the zero calibration reading for future reference and
agreement checks of the zero stability.
Note the instrument zero reading should typically be between 10-20%
of full scale calibrated range (chosen at the factory), This reading
should always repeat on nitrogen with the zero offset and/or
flag introduced. If not, readjust the instrument fine or coarse zero
potentiometer (s) or microprocessor/computer etc., to read the
correct concentration value known (determined after the original on-
line process calibration).
Span calibration check after performing a process on-line calibration.
After zero calibration above.
To check span on the analyzer, immediately back-flush out the
process fluid and dry the cell with a reproducible zero fluid that does
not contain any of the analyte. In this case, nitrogen or dry air
(typically -75 ‘C dew point or less than 1 PPM water) should be
used. Manually introduce the span flag from the readout control unit
to operate the solenoid containing the appropriate span filter into the
light path of the analyzer (this may be automatically or manually
operated depending upon the sample system and electronic instru-
ment design). RECORD the span calibration reading for future
calibration reference of the span sensitivity agreement. The filter
span flag is chosen at the factory to represent an upscale reading of
typically between 60-90% of the full scale range.
NOTE: The zero or span flag readings should always repeat if the
analyzer remains in calibration. Any drift in the zero or span can