Thermo Scientific 42i Instruction Manual page 148

Calibration
Calibration in Dual Range and Auto Range Mode
Alternative Calibration
Procedure Using NO
Permeation Tube
Calibration in Dual
Range and Auto
Range Mode
Set NO and NO
Background Readings to
4-16 Model 42i Instruction Manual
Although it is recommended that a GPT system be used to calibrate the
analyzer, the procedure described in the Code of Federal Regulations, Title
2
40, Part 50, Appendix F using a NO
alternative procedure for calibrating the instrument.
The dual/auto range calibration feature is used to calibrate the analyzer at
two different span levels (as opposed to a single span level in the standard
mode) generating a "tailored multi-point" calibration curve stored in the
analyzer's memory. This feature may be used:
When widely different gas levels are being monitored, such as a factor
●
of 10 or greater apart
If precision and span levels are being introduced using separate tanks
●
If more than one multi-component cylinder is being used to calibrate
●
the instrument
Properly designed chemiluminescence analyzers are inherently linear over a
wide dynamic range; and under normal USEPA compliance situations this
feature is not required. Dual calibration may be used for span levels less
than a factor of 10 apart, however if this is done to correct for a significant
non-linearity, it may mask the problems causing the effect, such as, bad
calibration cylinder, leaks in sampling lines, or low ozonator output.
Use the following procedures to calibrate the analyzer in dual or auto range
mode.
Use the following procedure to set the NO and NO
x
to zero. Both the Set NO background and NO
operate the same way, and the following procedure also applies to the NO
Zero
and NO background screen.
x
For detailed information about the menu parameters and the icons used in
these procedures, see the "Operation" chapter.
1. Follow the "Pre-Calibration" procedure described previously in this
chapter.
2. Introduce zero air to the SAMPLE bulkhead and allow the analyzer to
sample zero air until the NO, NO
permeation tube may be used as an
2
background readings
x
background screens
x
, and NO responses stabilize.
x 2
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