INFICON Composer Gas Concentration Controller - Manual (Page 92)

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Composer Operating Manual
15 Enter these values through the menu Setup >> Process Parameters. Also,
select the control loop type of your choice.
16 Press the SEND button on the pop up window. Now is the time to verify the
control loop's actions with the new found process parameters.
17 Wait until the mole-% returns to zero and steady light is illuminated. 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 bubbler flow. In the same manner, verify that the other control loop
type also works with the same set of process parameters.
18 When finished, press STOP button to terminate all gas flows.
3.2.3.2 Using Composer’s System I/O Interface
The standard system I/O interface contains electrical connections for all
instrument required operating commands (see
section 4.3.6.1, Description and
Purpose of SYSTEM I/O Connector, on page 4-22 ). A simple user interface may
be built with momentary contact push button switches and status LEDs.
Using the Setup software, configure the instrument for control with appropriate
gas flow parameters. Use reasonable guesses for control parameters (such as,
PROCESS GAIN = 2.0, DEAD TIME = 5 sec, TIME CONSTANT = 10 sec).
If the reactor is configured with bypass or dilution plumbing, use the BYPASS
input to start carrier gas flow. When stable conditions are achieved, zero the
instrument using SET ZERO input.
Enter the control mode by using the START CONTROL input. The bubbler gas
flow will slowly increase. When reasonable gas flow is achieved, activate the
HOLD input to maintain fixed gas flow rates.
Wait until the measured concentration ceases to increase. Compute process
gain from the knowledge of concentration and the bubbler flow rate. For
example, if the stable concentration reading is 0.2 mole-% and the bubbler flow
rate is 20 sccm through a mass flow controller of 200 sccm capacity, then the
controller output is 0.5 volt (5 volt * 20 sccm / 200 sccm). Consequently, the
process gain, Kp, is 0.4 (0.2 mole-% / 0.5 volt).
Activate the BYPASS input again to stop the bubbler flow. Use a stopwatch or
timer to determine the dead time (time interval between the stopping of bubbler
flow and a noticeable change in the concentration reading). In the same
manner, determine the time constant, by measuring the time interval between
the start of concentration change and its falling to 37% of the original
concentration reading.