Teledyne LGA-3500 - Laser Gas Analysis system - Manual (Page 81)

Laser Gas Analyzer Maintenance and Calibration
Teledyne Analytical Instruments 67
Maintenance and Calibration
The Model 3500 Laser Gas Analysis System needs to be
maintained and calibrated periodically to ensure it is working properly.
6.1 Maintenance
There are no user serviceable parts within the Model 3500. Daily
preventive maintenance is limited to:
• Checking and adjusting the purge gas flow
• Visually inspecting and cleaning the optical devices
• Optimizing the optical transmission.
The Model 3500 Laser Gas Analysis System incorporates a purging
system to protect the optical parts in the transmitter unit and the receiver
unit from contamination by dust, water vapor, and process gas
deposition. Maintaining an appropriate purge gas flow rate is a key
factor in its ability to keep the components functioning. However, dust
and other pollutants in the environment still could contaminate the
optical parts during extended operation of the system which would result
in lower the transmittance between the transmitter and receiver as well
as influence the overall performance of the system. For this reason it is
important to clean the optical parts periodically. Drift in the optical
transmission alignment may also occur after a period of time, and needs
to be re-adjusted and optimized periodically.
The Model 3500 uses specially designed signal processing circuits.
As long as signal voltage from the sensor is no less than 30% of its
normal value, the system measurement and analysis performance is not
affected. It greatly reduces the demand of cleaning the optical parts and
re-adjusting the optical transmission alignment.
6.1.1 Adjusting the Purge Gas Flow
The purge system is equipped with a gas regulator which provides
steady purge gas flow even when the gas source pressure fluctuates over
a large range. However, if excessive dust or other particles are present in