3-46 | Model 931S / Model 932S UV Analyzers
Optional pressure transducer (pressure compensation):
The analyzer pressure – if the optional pressure transducer is used – can
also be used to set the sample flow rate by first measuring the sample
stream pressure with no flow (Metering Valve or Drive Air Isolation Valve
closed) and then adjusting the Metering Valve (or Aspirator Drive Air
Regulator with the Drive Air Isolation Valve open) to obtain a pressure of
5–10 mmHg less than the value obtained with the valve closed. Check the
Measuring Cell pressure (Cell Pres) on the Analog Inputs dialog box.
To avoid damaging the pressure transducer, do not set the pressure
higher than the pressure transducer rating, either 0–210 kPaa,
(0–30 psia), 0–700 kPaa (0–100 psia), or 1380 kPag (200 psia) for the
0–3450 kPaa (0–500 psia) transducer.
1380 kPag (200 psia) is the maximum Cell Pressure allowed for the
analyzer certification.
For more information about the pressure compensation option, refer to
“Cell/Miscellaneous (Compensations) Parameters” in Chapter 4.
Setting the Zero Gas Flow Rate
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 analyzer are
stable and further increases in Zero gas flow rate do not reduce the con-
centrations observed in the analyzer System 200 Software (Status tab).
is necessary to get a good zero response. To obtain a good Zero gas flow
rate, adjust the rotameter for a flow rate of 1 L/min (2 SCFH).
If the Zero gas flow is set too high, the Zero gas cylinder will need to be
changed more often. It is important to note that in the simplest analyzer
configuration with only one solenoid, if the analyzer is powered down
or has a fault, the analyzer will flow Zero gas. A very high or prolonged
Zero gas flow will empty a Zero gas cylinder fairly quickly when there is a
fault. This is less critical if plant nitrogen or instrument air is being used as
the Zero gas.
Set the response time first to ensure a good zero.
Some applications may require a higher flow rate.
NOTE
Setup (tab)Analog
Inputs
!
CAUTION
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