Thermo 42i - Connecting the GPT Apparatus

Calibration
Calibration
Thermo Electron Corporation Model 42i Low Source Instruction Manual 4-3
42i Low Source, and then reintroduced to the instrument. The Model 42i
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 42i 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.