320 Rockwell Automation Publication 2080-UM002M-EN-E - April 2022
Appendix E PID Function Blocks
Troubleshooting an
Autotune Process
You can tell what is going on behind the autotune process from the sequences
of control output. Here are some known sequences of control output and what
it means if autotune fails. For the ease of illustrating the sequence of control
output, we define:
•Load: 50
•Step: 20
PID Application Example
The illustration above shows a basic water level control system, to maintain a
preset water level in the tank. A solenoid valve is used to control incoming
water, filling the tank at a preset rate. Similarly, outflowing water is controlled
at a measurable rate.
IPID Autotuning for First and Second Order Systems
Autotune of IPID can only work on first and second order systems.
A first order system can be described by a single independent energy storage
element. Examples of first order systems are the cooling of a fluid tank, the
Output Sequence 1: 50
→ 70 → 30
Sequence Condition Autotune Result Action for Autotune Fail
Process value reached 'first peak' and 'second'
peak in time
Likely successful NA
Output Sequence 2: 50 → 70 → 50
Sequence Condition Autotune Result Action for Autotune Fail
Process value not able to reach 'first peak' Likely unsuccessful Reduce Deviation or Increase Step
Output Sequence 3: 50 → 70 → 30 → 50
Sequence Condition Autotune Result Action for Autotune Fail
Process value not able to reach second peak Likely unsuccessful Increase Deviation or increase Step
Output Sequence 4: 50 → 70
Sequence Condition Autotune Result Action for Autotune Fail
Process value not able to reach First peak in
time
Likely unsuccessful Increase ATDynamSet
Water In
Water Level
Tank
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