4 an example of computation – INFICON Composer Gas Concentration Controller User Manual
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Composer Operating Manual
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Enter the programming mode again. Modify the process parameters with
newly found values. Also, select the control loop type of your choice. Exit
programming mode. Now is the time to verify the control loop's actions with
the new found process parameters.
15
Wait until the mole-% returns to zero and steady light illuminates.
16
Press the START button to initiate control loop action. This should verify
that the loop parameter values are reasonable. When satisfied, press
BYPASS to terminate the bubbler flow. In the same manner, verify that the
other control loop type also works with the same set of process parameters.
17
When finished, press STOP button to terminate all gas flows.
3.2.3.4 An Example of Computation
This example applies to all the cases described above. Suppose, the bubbler
MFC's full scale is 500 sccm and is flowing 100 sccm in steady state. If the
displayed concentration is 2 mole-%, then the control output is (5 V*100/ 500)
= 1.0 volt. The process gain = (2 mole-% / 1.0 V) = 2 mole-%/volt.
When the concentration reaches 1/e of its steady state value, it will be (2
mole-% * 0.37) = 0.74 mole-%.
Let us assume that, after the bubbler flow is stopped it takes 7 seconds for the
concentration to start to fall. So, the dead time is 7 seconds. If it takes 28
seconds for it to reach 0.74 mole-%, then the time constant is (28 sec - 7 sec)
= 21 seconds.
3.2.4 What if the NOVRAM’s Battery Fails and
I Lose All My Stored Parameters?
The expected life for the nonvolatile memory used in the Controller is in excess
of 10 years. Therefore, failure shouldn’t happen very soon; but when it does, be
prepared. It is much easier to restart if you have a copy of all of the parameter
values for each Controller. This can be a record saved on a floppy disk or on
paper, preferably stored in several places. Replacement of the NOVRAM
should be done by a factory representative. Refer to
and Repair Support, on page 1-4
for information on how to get help.