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THEORY OF OPERATION M300EU
Addendum to M300E/EM Manual P/N 04288
The auto-reference measurement takes approximately 15 minutes. To ensure that the sample chamber of the
optical bench is properly purged when switching between the sample and auto-reference measurements and
vice-versa, each auto-reference cycle includes a 3 minute dwell period before and after the actual
measurements are made. This cycle is restarted every 4 hours by an ACAL sequence, programmed at the
factory (see Section 6.4).
Figure 10-2: Auto-Reference Measurement Cycle
10.2. PNEUMATIC OPERATION
With the exceptions to the difference discussed on other portions of this addendum regarding the A-REF CO
scrubber and the Nafion
®
dryer, (See Sections 3.2, 5.1.1, 5.1.2, 5.1.3, 10.1.1 & 0) the pneumatic operation is the
same as that described in Section 10.3 of the M300E/EM Operators Manual (P/N 04288).
10.2.1. THE A-REF CARBON MONOXIDE SCRUBBER
A special CO scrubber is used to remove all of the CO from the gas stream when the instrument is performing
an auto-reference measurement. The scrubber contains a substance that catalyses a chemical reaction
converting any CO in the gas stream to CO
2
.
NOTE
To operate properly, the gas flowing though the scrubber must contain at least 5% O
2
.
This includes calibration gases such as zero air and span gas.
The O
3
scrubber is located inside the auto-reference valve assembly.
50 05831 Rev. 01