Calibration
Calibration in Dual Range and Auto Range Mode
4-12 Model 42i Low Source Instruction Manual Thermo Electron Corporation
Calibration in Dual
Range and Auto
Range Mode
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 NO and NO
x
background readings to
zero. Both the Set NO Background and Set NO
x
Background screens
operate the same way, and the following procedure also applies to the Set
NO
x
background screen.
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
x
, and NO
2
responses stabilize.
3. When the responses stabilize, from the Main Menu choose Calibration
> Calibrate NO Background.
4. The Set NO Background screen displays the current NO background
and NO concentration.
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