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Teledyne Analytical Instruments
11
Thermal Conductivity Analyzer Model 212R
2.3.4 Installation of Cylinder Supplies.
The reference and standard gas cylinders should be installed as close to the
analyzer as possible. Each cylinder should be provided with a dual stage,
metallic diaphragm, pressure reducing regulator. When installing the regulators,
crack the cylinder valve open so that gas is flowing. This procedure will prevent
air from being entrapped in the regulator, and eliminate a common source of
supporting gas contamination. Improper installation of a cylinder regulator can
appreciably change the composition of a standard gas. Air trapped in the regula-
tor will diffuse back into the cylinder, and the impurity concentration of the
composition will be altered. When dealing with the zero gas, the alteration of the
composition can be significant.
Once installed, prior to use, the regulators for reference, span and zero
gases must be purged by alteratively pressuring the first stage, with the second
stage off, then bleeding out the first stage by opening the second stage, back and
forth several times.
Note: Make sure to close the cylinder prior to bleeding the first stage
through the second.
2.3.5 Sample Pressure.
The sample point should be equipped with a metallic diaphragm pressure
regulator and the pressure reduced to between 10 and 50 psig. The regulator
should be installed as close to the sample point as possible to minimize sample
line lag time.
2.3.6 Interconnecting Lines.
The inlet and vent connections are identified on the analyzer outline dia-
gram. The connections are stainless steel 1/8" female pipe couplings that are
braised into a gas connector bar mounted within the analyzer. The braised pipe
coupling was selected as a transition so that the torque generated during installa-
tion of the external system would be isolated from the internal system. Bulkhead
type fittings can be accidently twisted, and leaks promoted in hard to reach areas
within the analyzer. TAI suggests that 1/4" tubing and adapter fittings be used
throughout the external sampling and supporting gas system.