control relay and the controlling device.
Relay
on
off
period
period
period
etc.
7.10
Setting up the PI pulse width controller
1. Set the
A
x
OPEr
function to
A
x.
tP
.
2. Set the control setpoint
A
x.
SP
to the required setting.
3. Set the control span
ctrI SPAN
to the required setting.
4. Set the proportional gain
A
x.
PG
to an arbitrary value e.g.
0.500
.
5. Set the integral gain
A
x.
IG
to
0.000
(i.e. off).
6. Set the low and high integral
A
x.
IL
and
A
x.
IH
limits to an arbitrary value e.g.
20.00
.
7. Set the bias
A
x.
bs
to
50.0
.
8. Set the cycle
A
x.
dc
period to
20
seconds.
Initialise the control system and monitor the control results. If the original settings causes process
oscillations then gradually decrease the proportional gain until the oscillations decrease to an
acceptable steady cycle. If the original settings do not cause process oscillations then gradually
increase the proportional gain until a steady process cycling is observed.
Once the steady cycling state is achieved note the difference between the display value and the
control setpoint value. Gradually increase or decrease the bias value until the displayed value
matches (or cycles about) the control setpoint value.
Gradually increase the integral gain until the process begins to oscillate. Then reduce the integral
gain slightly to regain the control without this added oscillation.
Create a step change to the process conditions and observe the control results. It may be necessary
to fine tune the settings and use integral limits to obtain optimum results.
Set up sequence
Symptom
Solution
Proportional gain
Slow response
Increase proportional gain
Proportional gain
High overshoot or oscillation
Decrease proportional gain
Proportional bias
Process above or below setpoint
Increase or decrease bias as required
Integral gain
Slow response
Increase integral gain
Integral gain
Instability or oscillations
Decrease integral gain
40 of
RM4AVMAN-2.1-0
