PID Proportional-Integral-Derivative Control
Proportional-Integral-Derivative Control (PID) function blocks implement a standard PID control algorithm.
|Name||Function block name, see common parameters|
|DYN dynamic option, see common parameters|
|/||Mixed inputs option, see common parameters|
|Input||The measured value or (process value) that is to be controlled.|
|Set Point||The target value (set point) that the control block is striving to attain.|
|Control parameters||Proportional||Control's Proportional setting.|
|Integral||Control's Integral setting.|
|Derivative||Control's Derivative setting.|
|Deadband Increasing/Decreasing||If the error value is less than this value the control will not change its output. This can help prevent unnecessary cycling. There are two separate parameters which are applied depending on whether the output would be increasing or decreasing.|
|Ramp Rate||Limits the rate at which the output is allowed to change, the value is expressed as % per second. For example, if set at 20 a step PID output change from 0 to 100% would require 5 seconds to ramp up to 100%.|
|If defined allows a digital input block to temporarily enable or disable the PID algorithm. When disabled the output goes to zero also it becomes possible to set the output value directly, via MBus_ioFlash or Modbus. When enabled the output will ramp to its required value over the entered "Ramp Time" interval.|
|/||Toggles between Reverse and Direct acting
(push to switch between modes):
- In Reverse mode, the PID response is in inversely proportional with the weighted sum of the control parameters, heating application for example.
- In Direct mode, the PID response is in direct proportion with the weighted sum of the control parameters, cooling application for example.
This parameter can also be dynamically controlled by another block in the MBus_ioFlash program.
PID Control Algorithm Primer
controller (PID controller) attempts to correct the error
between a measured process variable and a desired set point
by calculating and then outputting a corrective action that can adjust the
PID controller algorithm involves three separate parameters; the Proportional,
the Integral and Derivative values. The Proportional value
determines the reaction to the current error, the Integral
determines the reaction based on the sum of recent errors and the Derivative
determines the reaction to the rate at which the error has been changing. The
weighted sum of these three actions is used to adjust the process via a control
element such as the position of a control valve or the power supply of a heating
"tuning" the three constants in the PID controller algorithm the PID
can provide control action designed for specific process requirements. The
response of the controller can be described in terms of the responsiveness of
the controller to an error, the degree to which the controller overshoots the
setpoint and the degree of system oscillation. Note that the use of the PID
algorithm for control does not guarantee optimal control of the system.