Cell Calibration And Offset - Ametek 2850 User Manual

Cell Calibration and Zero Offset
Cell calibration is achieved by measuring the moisture concentration of the reference
gas after a known quantity of moisture has been added to it by the moisture genera-
tor. The measured value is compared to the known value stored in memory and the
moisture span (the system constant Moist_Span) is adjusted accordingly. Refer to the
Calibration Data Sheet supplied with the analyzer for the precise moisture generator
value.
The Calibration Cycle can be initiated on demand (see Calib Button, below) or config-
ured to run automatically at a user set interval (see Set Auto-Cal Time, (Chapter 4)).
Depending on how the system is configured, the moisture span will be verified or ad-
justed during the auto-cal cycle and then the system will return to normal operation.
Note that when a new span value is calculated, the new value will be compared to
the Max_Span_Err and Max_Span limits stored in memory. If the new value exceeds
these limits, the system alarm will be activated. Refer to (Chapter 4): Alarms and
Alerts for an explanation of these two limits and information on setting and changing
them.
For extremely low concentration (< 1ppm) applications, the analyzer cell must be ze-
roed before calibration. The offset frequency between the sample and reference gases
is measured and is used to adjust the value of polynomial coefficient D (the system
value PolyCoeff_D). This value is part of the polynomial expression used to calculate
moisture concentration. The offset frequency can vary over time and the value of
coefficient D must be verified periodically and adjusted when necessary.

NOTE
If analyzer is properly configured, the zero cycle can be run automatically (see Start
Auto-Zero, (Chapter 4)) or manually (see Flow Dry Sample, (Chapter 4)). Depend-
ing on how the system is configured, coefficient D will be verified or adjusted during
the zero cycle and then the system will return to normal operation. Note that when
a new coefficient D value is calculated, the new value will be compared to the Max_
Zero_Err and Max_Zero limits stored in memory. If the new value exceeds these
limits, the system alarm will be activated. Refer to (Chapter 4): Alarms and Alerts for
an explanation of these two limits and information on setting and changing them.
Calib Button
CALIB
To access the Calibration Menu, press the
the desired menu item is highlighted and press
for information on setting the various calibration and zero cycle timers (the system
variables Cal_Cycles, Zero_Cycles, and Equil_Cycles).
4-4 2850 Moisture Analyzer
Additional external valves and sample connections are required to run the zero
functions. Please refer to Figures C1 and C2 in Appendix C for the proper con-
figuration. External valves used to switch gas through the external dryer must be
opened manually before zero cycle and closed following zero cycle.
button. Scroll through the menu until
calib
. Refer to (Chapter 5): Timing
enter