INFICON Composer Gas Concentration Controller User Manual
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Composer Operating Manual
3.2.3.3 Using Composer’s Front Panel Keypad (LCD Display
Option)
1
Press the PROG button on the keypad to enter programming mode. Set
appropriate MFC parameters, gas parameters and total gas flow. Choose
reasonable values for target concentration, process gain, dead time and
time constant parameters. These are temporary values which will be
modified later.
2
If total flow is to be conserved, the DIP SW#5 on CFGR2 must be set.
3
Connect MFC control cables to the back of the instrument. Press PROG
button again to end programming mode.
4
Evacuate the cell and gas line.
5
Press the BYPASS button on the keypad to start dilution gas flow. When line
pressure stabilizes, the concentration steady sign illuminates.
6
Press REF ZERO on the keypad to establish pure carrier gas frequency.
7
Now press the START button on the keypad. This will activate the control
loop, thus initiating bubbler gas flow.
8
Watch the displayed concentration. If the response is too slow, enter the
programming mode again, reduce the process gain value and then exit
programming mode. In this manner, keep adjusting the gas flows until the
concentration is in the neighborhood of your desired operating point.
9
Press the HOLD button to maintain gas flows at the present rate and wait
until the concentration stable sign is on.
10
When the concentration steady sign illuminates, note the bubbler flow by
pressing the B button on the keypad. Also note the displayed mole-%.
11
Compute:
bubbler control output as (5.0 volt)*(bubbler flow)/(bubbler full scale)
Process Gain as (displayed mole-%)/(bubbler control output).
12
Compute 1/e of the steady state concentration value as
(displayed mole-%)* 0.37.
13
For this step, use an external timer/stop watch. Reset the timer. Immediately
press the BYPASS button on the keypad. Observe the displayed
concentration. Note the time at which the concentration starts to fall. This is
approximately the dead time. Note the time at which the displayed mole-%
reaches approximately 37% of its original value. This time is the sum of the
dead time and the process time constant. Thus, all three process
parameters are known.