Example: How To Create A Feedback Loop For The Manipulated Value - Allen-Bradley Micro800 General Instructions Manual

Programmable controllers

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Table of Contents

Proportional Integral Derivative (PID) instruction

Input parameters

Warning for the Auto Tune sequence. Possible values are:

0 - no auto tune done.

1 - in auto tune mode.

2 - auto tune done.

-1 - ERROR 1 input automatically set to TRUE, no auto tune possible.

-2 - ERROR 2 auto tune error, ATDynaSet expired

Gains calculated after AutoTune sequences.

Example: How to create a feedback loop for the manipulated value

Adding a feedback loop for the manipulated value prevents excessive overshooting

by providing a minimum and maximum value for the MV.

Temperature feedback loop example

At the beginning of the temperature control process, the difference between the

process value (PV) and the setpoint value (SP) is large, as shown in the following

graph. In this example of a temperature feedback loop, the PV starts at 0 degrees

Celsius and moves towards the SP value of 40 degrees Celsius. Notice also that the

fluctuation between the high and low manipulated value (MV) decreases and

stabilizes with time. The behavior of the MV depends on the values used in each of

the P, I, and D parameters.

Rockwell Automation Publication 2080-RM001D-EN-E - February 2015