INFICON Composer Gas Concentration Controller - Manual (Page 82)

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Composer Operating Manual
3.1.15 How to Sample Flow with a Composer
When the flow through a pipe exceeds the Transducer’s 1800 sccm limit,
sampling of the process is required. In our experience simply bypassing some
of the process gas through the Transducer can compromise the Composer’s
precision, long term accuracy and add noise due to pressure and flow
fluctuations.
Our recommendation is to “buffer” the flow through the transducer by adding a
Mass Flow Controller (MFC) upstream of the Transducer in the sample line.
This device will stabilize the flow and in most cases restore the instrument’s full
measurement capability. In some extreme cases it may be necessary to also
add downstream buffering with a Back Pressure Controller. Try to maintain at
least 100 Torr in the Transducer for best operation. It may be necessary to
slightly restrict the process tubing in order to induce flow through the sample
tube. See
Figure 3-8 .
An added benefit of adding the MFC to the sample tube is that flow through the
Transducer is made visible and easily verified.
Figure 3-8 Flow Sampling
MFC
Composer
Transducer
Composer
Controller
Read
Out
Back
Pressure
Controller
Pump
May require restriction to induce
flow through sample tube.
Optional;
For maximum
sensitivity or if
severe instability
exists.