Metek 920, Operator'S Manual With Essential Health And Safety Requirements

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Installation and Start-Up | 3-43
4. Record the analyzer’s initial Measure and Reference PMT signal read-
ings. See “Recording Initial Readings” in this chapter.
5. Change the Flow Control mode back to “ 0 ” ( Analyzer Control ).
6. Return to RUN mode.
7. Turn off the Zero gas.
The Zero is complete and the analyzer is now on-line.
Setting the Zero Gas Flow Rate
When the flow control solenoid is in a de-energized state, instrument
air flows into the sample path via a flow controlling rotameter and a
Manifold. The Zero gas flow rate must be high enough to adequately
purge the Measuring Cell of sample gas to obtain a “good zero.” A
good
zero can be defined as a state where the concentration outputs of the ana-
lyzer are stable and further increases in Zero gas flow rate do not reduce
the concentrations observed on the analyzer User Interface. A nominal
flow rate of 5–10 SCFH should be sufficient for this purpose.
Set the response time first to ensure a good zero.
Some applications may require a higher flow rate.
Since excess air flow into the analyzer sample system will cool the
Measuring Cell and Analyzer Oven, the optimum Zero gas flow rate is the
lowest consistent with a good zero.
During warm-up of the sample system or when the analyzer is in
Standby, a lower Zero gas flow will decrease the cooling effects of pro-
longed air running throughout the sample system. The most important
factor during these conditions is to keep the sample system free of con-
tamination by the sample gas.

(FlowCtrl) CAL

F5 2

Del 0 Ent Ent

NOTE