5.2 Instrument Checks
The instrument requires little maintenance, other than the filter column (if fitted), source block
purge (if fitted), sample flow adjustment (if necessary), and zero and span adjustment (see
section 4).
5.2.1 Source Block Purge (when fitted)
Certain instruments fitted with the ‘SB’ type IRGA bench have a CO
2
trap to remove traces of
the gas from the source block. The trap is a glass jar which protrudes through the front panel
of the instrument, filled with indicating soda lime (see section 2.8.2). The colour of the soda
lime should be checked regularly, and the contents replaced when only the very end of the jar
remains green. The jar is removed by unscrewing.
When replacing or handling chemicals, avoid physical contact and wash hands
afterwards.
Dispose of chemicals carefully and in accordance with any local Health & Safety
requirements.
5.2.2 Filter Column (when fitted)
If a Filter Column is fitted, regularly check the condition of the chemical it contains. The
characteristic to look for when the chemical is exhausted depends on that used and is described
in Section 2.8.
Replace the chemical before it is completely exhausted to avoid subsequent ‘hang-up’. If it is
used in an exhausted state it may cause unstable operation of the Instrument.
When replacing or handling chemicals, avoid physical contact and wash hands
afterwards.
Dispose of chemicals carefully and in accordance with any local Health & Safety
requirements.
5.2.3 Sample Flow
Once set, sample flow should not require adjustment unless it moves near the shaded areas on
the flow meter. Before adjusting flow internally, check sample and exhaust piping for
obstruction, state of filters etc.
If necessary, adjust the flow using the pump speed control (RV2 on the power supply board) or
sample throttle (when fitted).
If the flow continues to fall off over a period of time, it may indicate that the lines are becoming
blocked, as indicated in the previous section.
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