PID ProportionalIntegralDerivative Control 
ProportionalIntegralDerivative Control (PID) function blocks implement a standard PID control algorithm.
Parameter  Description  
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%.  
Enable
& Ramp Time 
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
control mode
(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 PrimerA proportional–integral–derivative
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
process accordingly. 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
element. By
"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.
