Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 26)

3) Exit the Real Time display mode.
4) Exit the TGA program.
5) Shut off power to the TGA PC and monitor.
6) Shut off the TGA sample pump.
7) Shut off power to the TGA enclosure.
8) Shut off the reference gas supply.
9) Shut off the air gap purge supply, if applicable.
10) Shut off calibration gas supplies, if applicable.
If the TGA100 is not to be operated for an extended period, allow the laser to warm up. If the laser is to be operated
again in the near future, it is recommended to keep the laser cold to avoid temperature cycling the laser.
2.3.3 System Checks
The TGA100 is often used for long term continuous measurements. It is necessary to periodically check the status of
the system, perform routine maintenance, and transfer data for offline analysis.
1) Look for a message printed in red above graph 1 indicating the system has restarted. If it has restarted, it is
important to verify it is on the correct absorption line.
2) Verify concentration data collection and site means or gradient mode are ON (if used).
3) Verify the line lock is ON. If the TGA100 is in dual ramp mode, also verify the Ramp B line lock is ON.
4) Note the DC current (it is recommended that this be recorded in a log book). Compare it to the expected value to
verify the laser is still operating on the desired absorption line. If the TGA100 is in dual ramp mode, also note the
Ramp B offset.
5) Verify that the concentration and concentration noise are as expected. If the TGA100 is in dual ramp mode, also
verify the Ramp B concentration and noise.
6) Note the sample pressure (it is recommended that this be recorded in a log book). Compare this to the previous
values. The pressure will decrease over time as the sample intake filter(s) becomes plugged.
7) Note the laser heater voltage (it is recommended that this be recorded in a log book). Compare this to the previous
values. The vacuum inside the laser dewar will gradually degrade. This degradation reduces the thermal isolation
between the outer wall of the laser dewar and the laser itself. Over time, as more heat is transferred to the laser by
the degraded vacuum, less heat is needed to maintain the laser at the set temperature, and the laser heater voltage
will gradually decrease. Therefore, monitoring the laser heater voltage may give an indication of when it is time to
evacuate the dewar. This is especially important for cryocooler systems and for lasers that must operate at very
cold temperatures.
8) Exit the real time screen and stop the TGA program.
9) Download data. The details will vary from one system to another. The data can then be transferred by copying to
CD ROM, Zip disk, etc. Check the files to verify the expected files are present.
10) As soon as the data are downloaded, restart the TGA program and go to the real time screen. This will let the laser
and detector temperatures stabilize as the next steps are completed.
11) If needed, fill the laser dewar with liquid nitrogen. If the TGA is equipped with liquid nitrogen cooled detectors,
fill these as needed.
12) Check the reference gas tank and regulator pressure. Check other tanks (air gap purge, calibration, etc.) as needed.
13) If a change in the sample pressure indicates the sample intake filter(s) must be changed, shut off the sample
vacuum pump. Wait for the pressure to reach ambient, and then replace the filter element(s). Restart the sample
vacuum pump.
14) Restart the TGA (see section 2.3.1).
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