Teledyne LGA-3500 - Laser Gas Analysis system - Manual (Page 82)

Maintenance and Calibration Model 3500
Teledyne Analytical Instruments 68
the purge gas source, the filter may clog after a period of time. This will
result in a fluctuation flow rate.
When a drop in the flow meter reading occurs, adjust the needle
valve (Figure 3.6) on the apparatus to increase the flow rate. If the
required flow rate cannot be achieved by opening the needle valve, the
filter is probably clogged and needs to be replaced.
To replace the filter cartridge:
1. Turn off the purge gas source.
2. Remove the screw on the side of the purge housing and remove
the filter (Figure 3.6).
3. Open the filter, and replace the old filter cartridge with a new
one. See the Parts Listing in the Appendix for the proper part
number for your instrument.
4. Reinstall the filter into the housing and fasten the screw.
5. Turn on the purge gas source.
6. Adjust the needle valve and set the flow rate to its the required
value.
CAUTION: DO NOT SHUT OFF THE PURGE SYSTEM TO
CHANGE THE FILTER CARTRIDGE WHEN THERE IS
GAS FLOW IN THE ENVIRONMENT UNDER TEST.
POLLUTANTS IN THE ENVIRONMENT COULD
DAMAGE THE OPTICAL PARTS.
6.1.2 Clean the Optical Parts
For most applications, the time interval to do optical parts cleaning
usually exceeds 3 months. Even for highly dusty applications, with
proper purging, the optical parts are kept clean for a relatively long time.
TAI recommends cleaning the system optical parts once every two or
three months to ensure that the system will run continuously and
dependably with minimum downtime. If the purge system malfunctions,
check the optical parts for contamination.
The optical transmission information is shown on LCD screen. The
transmittance decreases when the optical parts become dirty or the
optical transmission alignment between the transmitter and receiver is
off from the optimal position. The transmittance information thus can be
used as an indicator to determine whether the optical parts need cleaning