Zener 8000 Application Manual page 14

Application SW08024: PID Irrigator
PID Tuning Guide
The Proportional gain:
Prop. Band value is the proportion of input required to generate 100% at the output of the PID control. For
example H01 Prop. Band is 200.0%, the proportional gain is 100/200 = 0.5. That is 2 units of input will generate
1 unit of output. The higher the % value, the lower the 'proportional gain'.
The integral time: The integral action adds a corrective component to reduce a constant error difference
between set point and feedback signals. The greater the error, the quicker the gain increases. The H02 Integ.
time value sets the time to 'repeat' the error difference between set point and feedback signals - This assumes
the Proportional gain is equal to 1.
A low H02 Integ. time value attempts to regulate the process variable quickly. However if excessively low, over
shooting and under shooting will be more prominent.
A high H02 Integ. time value diminishes over shooting and under shooting. However regulation takes longer to
achieve.
Guide to PID Tuning:
The guide below assumes short ramp times. Long ramp times will dominate system
performance and the steps below will have little or no effect.
Step Problem
The plumbing is set for typical flow
but the system responds too slowly
1.
The system starts to overshoot or
oscillate
2.
The system still responds slowly
(after adjusting H01 Proportional
3.
band )
The system starts to overshoot or
oscillate
4.
(after initial adjustments to H02
Integral Time )
Page 13 Document: IM00160A
amplifies the difference between the set point reference and feedback signals. The H01
Action
1.1 Stop the ZENER 8000 & pump
1.2 Halve the value of H01 Proportional band. Avoid adjustments below 10%.
1.3 If H01 Proportional band is below 10% proceed to step2.
1.4 Stop & restart the ZENER 8000 & pump.
1.5 Observe the time it takes to reach pressure (or reacts to changes)
1.6 Repeat from step 1.2 if the response is slow. Otherwise proceed to step 2.
2.1 Stop the ZENER 8000
2.2 Double the value H01 Proportional band
2.3 Start the ZENER 8000 and observe the time it takes to reach pressure or reacts to
changes
2.4 Repeat from step 2.1 if the system still overshoots or oscillates. Otherwise
proceed to step 3.
3.1 Halve the H02 Integral Time
3.2 Observe the time it takes to reach the pressure (or reacts to changes)
3.3 Repeat from step 3.1 if the response is still slow. Otherwise proceed to step 4
4.1 Double the H02 Integral Time
4.2 Observe the time it takes to reach the pressure (or reacts to changes)
4.3 Repeat from step 4.1 if the system still overshoots or oscillates
4.4 If the response is acceptable then you may stop tunning
15/07/19