Armfield Instruction Manual
104
Once again note the operation of the peristaltic pump and observe the fluid level in
the process vessel.
Wait until the oscillations in fluid level stabilise in magnitude and duration, then select
the
icon to finish data logging.
Create a new results sheet by selecting the
icon in the tool bar of the software.
Select the
icon to begin data logging.
Open valve SOL 2 so that both valves SOL 2 and SOL 3 are open. Note whether it is
possible to maintain the fluid level in the vessel by controlling the peristaltic pump
speed alone. If the fluid level remains stable, wait until the oscillations in fluid level
stabilise in magnitude and duration, then select the
icon to finish data logging. If
the fluid level falls continuously, wait until the level is 50mm below the Set Point then
stop logging.
Close both valves SOL 2 and SOL 3 and allow the fluid to return to the set point.
Set Point
Investigate the effect of changing the pressure Set Point for the controller:
Create a new results sheet by selecting the
icon.
In the software, alter the pressure switch set point to 100mm.
Select the
icon to begin data logging.
Continue logging until the oscillations reach constant magnitude and duration, then
select the
icon to finish data logging.
Repeat the procedure, altering the set point and recording the change in fluid level
until the oscillations reach stable values. Suggested values for the pressure switch
set point value are 150, 250 and 300mm. Remember to create a new results sheet
for each set of data.
PID Settings and optimisation
With proportional control action, the controller produces a signal that is proportional
to the error (the difference between the monitored variable and the set point value).
This creates an offset between setpoint value and actual value (the controller only
supplies an output when there is an error, so there is no controller output when the
value is not at the set point). It also generates an overshoot (the system will oscillate
above and below the setpoint value at the start of the control period until stability is
attained).
Without logging the data:
With the I and D settings at 0s (zero), observe the variations in fluid level.
Alter the setting for Proportional Band (P) in the software to 10%, and continue to
observe the variations in fluid level.
To Next Page
Loading...