Thermo 42i, Instruction Manual

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Calibration
Calibration
Thermo Electron Corporation Model 42
i
Low Source Instruction Manual 4-3
42 i Low Source, and then reintroduced to the instrument. The Model 42 i
Low Source should give identical responses to the test gases whether they are
introduced via the sample port or the zero or span ports. If not, the
plumbing and/or valves should be serviced.
The following procedure discusses calibration of the Model 42 i Low Source
analyzer using the gas phase titrator and zero gas generator previously
described. It is suggested that a calibration curve have at least seven points
between the zero and full scale NO concentrations. Although the
seven-point curve is optional, two of whatever number of points is chosen
should be located at the zero and 90% levels and the remaining points
equally spaced between these values.
Connecting the GPT
Apparatus
Use the following procedure to connect the GPT apparatus.
1. Assemble a dynamic calibration system such as the one shown in
Figure 4-1 .
2. Ensure that all flowmeters are calibrated under the conditions of use
against a reliable standard, such as a soap-bubble meter or wet-test
meter. All volumetric flow rates should be corrected to 25
°
C and 760
mm Hg.
3. Precautions should be taken to remove O
2
and other contaminants
from the NO pressure regulator and delivery system prior to the start of
calibration to avoid any conversion of NO to NO
2
. Failure to do so can
cause significant errors in calibration. This problem can be minimized
by:
a. carefully evacuating the regulator after the regulator has been
connected to the cylinder and before opening the cylinder valve;
b. thoroughly flushing the regulator and delivery system with NO
after opening the cylinder valve;
c. not removing the regulator from the cylinder between calibrations
unless absolutely necessary.