Filter Requirements; Flow Rate - GE Optica Operator's Manual

Filter Requirements

Flow Rate

Installation
If the gas to be monitored is free from particulates and hydrocarbon
liquids or vapor, filtering is not necessary. However, most sample gas
streams contain some particulates, and using a filter reduces the need
for frequent mirror cleaning. On the other hand, filtering tends to
slow the system's response, particularly at low frost points.
The series 912 filters manufactured by Balston Company (or
equivalent) are effective for most applications. For particulates and
liquid hydrocarbons, use a Balston type DX filter element.
To filter out very fine particles, the type DX can be followed by a type
BX filter. A type CI filter can be used to remove hydrocarbon vapors.
If the sample gas is heavily and routinely contaminated, we
recommend using a quick-change filter element. Avoid using glass
wool, cellulose, and other hygroscopic materials as a filter medium.
It is important to have adequate flow through the sensor. Too little
flow can slow the response (particularly at very low frost points). Too
much flow can cause instability of the control system at high dew
points and can reduce the depression capability of the thermoelectric
cooler at very low dew points. Too much flow also accelerates the
rate of system contamination. A flow rate of 2 to 2.5 ft3/h (a little
over 1 liter/min) is ideal for most applications. In many cases, flow
rates between 0.2 and 5 ft3/h (0.1 and 2.5 liter/min) may be used.
January 2006
2-15