Thermo Electron 48C, Instruction Manual

Page: 154 / 204

Chapter 9 Optional Equipment
TEFLON PARTICULATE FILTER
A 5-10 micron pore size, 2 inch diameter Teflon
→
element is available for the Model
43C. This filter should be installed just prior to the
SAMPLE
bulkhead. When using a
filter, all calibrations and span checks must be performed through the filter.
PURGE HOUSING
This housing is attached between the optical bench and Bodine8 motor faceplate
(Figure 9-8). It surrounds the gas correlation wheel and allows purging the area around
the gas correlation wheel with a gas other than that present in the local atmosphere. This
option increases reliability in the presence of contaminants that could interfere with the
analytical process. It should be noted that this setup is standard on the Models 41C and
41CHL.
Calibration note: The stability of the purge gas is very important. Since this gas is in the
same optical path as the sample, changes in the composition of the purge gas can change
the calibration of the instrument. Therefore, either zero air or a nontoxic dry inert gas,
such as nitrogen, is recommended for use in this option. Other than the effect of the
purge gas, operation and calibration of the instrument is not affected by the addition of
the purge housing.
A constant purge flow of approximately 140 cc/minute is recommended for optimum
performance. This is produced by feeding a purge gas to the rear panel bulkhead at a
constant pressure of 15 psig. A 0.006" glass capillary (green, TEI Part No. 4115),
mounted inside the capillary housing on the rear panel of the instrument will deliver the
required 140 cc/minute purge flow. Flows greater than this are not recommended due to
unstable cooling effects on the IR source. Lower flows are acceptable as long as the
purge housing is adequately purged for the application.
9-10