Calibration
Calibration in Dual Range and Auto Range Mode
Thermo Scientific
42iQ Instruction Manual
4-17
Where:
[NO
2
]
OUT
= NO
2
output concentration in ppm
P = permeation rate in μg/min
F
T
= total flow rate of gas after mixing chamber (F
P
+ F
D
) in liters/minute
K (NO
2
) = 0.382 constant for NO
2
permeant
Commercial permeation systems, such as the Thermo Scientific 146iQ
Multigas Calibration System, are available for this requirement. Refer to
the instrument instruction manual for more information.
In addition to the 146iQ and other commercial permeation systems, the
42iQ can also be configured with an optional permeation oven to supply
calibration gas for the instrument. The operation of the internal
permeation oven is described in Chapter 9, “
Optional Equipment
”.
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 U.S. EPA 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 procedure to set the NO and NO
x
backgrounds to zero.
Both the NO and NO
x
background screens operate the same way.
Note
The NO channel should be calibrated first and then calibrate the
NO
x
channel.
▲
Commercial Permeation
Systems
Calibration in Dual
Range and Auto
Range Mode
Set NO and NO
x
Backgrounds to Zero
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