INFICON Composer Gas Concentration Controller - Manual (Page 80)

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Composer Operating Manual
3.1.13.6 Determining Process Control Loop Parameters (Bulk
Flow)
3.1.13.6.1 Gain, Kp
The most important parameter for good feedback control in the Bulk Flow
Control configuration is K
p
. It is an easy one or two step experimental exercise
to determine this parameter.
Step 1- While in External (reactor) control, establish a “normal” flow of gas
through the bubbler. When stable, note the displayed concentration. Use this
value for the Concentration Target parameter and enter it into the Composer. If
this value is already known for a given bubbler and system, use that value.
Step 2 – Using your knowledge of the full-scale flow for the Bubbler’s MFC,
estimate its flow at 1 volt. Multiply this estimated flow by the Concentration
Target to determine the K
p
for the delivery system.
NOTE: Most MFCs provide full flow at 5 volts.
Example
Bubbler’s MFC full-scale flow is 200 SCCM
Full-scale flow is 5 volts
Concentration reading was 0.8500%
Calculate:
K
p
= [200 sccm / 5 V] * 0.85 = 34.00 sccm / V
3.1.13.6.2 Dead Time
For Bulk Flow Control set this parameter to 2 seconds initially, but never less
than 1.0 seconds.
3.1.13.6.3 Time Constant
For Bulk Flow Control set this parameter to 1 second.