Proportional Integral Derivative Function Block - Samson 3730-5 Configuration Manual

FOUNDATION™ fieldbus parameters
7.3.2

Proportional Integral Derivative Function Block

A PID Function Block contains the input channel processing, the proportional-integral-derivative
(PID) control loop and the analog output channel processing.
The configuration of the PID Block (PID controller) depends on the automation task.
Simple control loops, control loops with ouput value feedforwarding, cascade control and cas-
cade controls with limitation in combination with another controller function block can be imple-
mented.
The following options are available for data processing within the PID Function Block (PID con-
troller): Signal scaling and limiting, mode control, feedforward control, override tracking,
alarm limit detection and signal status propagation.
The PID Block (PID controller) can be used for various automation strategies. The block has a
flexible control algorithm that can be configured to match the application.
The PID Block receives its set point depending on the mode (MODE_BLK) from the input vari-
ables CAS_IN, RCAS_IN or SP. PV_SCALE, SP_HI_LIM, SP_LO_LIM, SP_RATE_UP and
SP_RATE_DN are used to generate an internal working set point.
The block receives the process value over the IN input variable which is used to generate the
process variable PV, taking into account the PV_SCALE and the filter of the first order
PV_FTIME.
These values are fed to the internal PID algorithm. This algorithm consists of a proportional, an
integral and a derivative component. The output value is calculated from the set point SP and the
process variable PV resulting from the system deviation.
The individual PID components are included in the calculation of the output variable as follows:
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Proportional component:
The proportional component reacts immediately and directly when the set point SP or the
process variable PV. The output variable is changed by the proportional factor GAIN.
This change corresponds to the system deviation multiplied by the gain factor. If a control-
ler works only with a proportional component, the control loop has a steady-state error
signal.
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Integral component:
The system deviation resulting from the calculation of the output variable using the pro-
portional component is integrated over the integral component of the controller until it is
negligible. The integral function corrects the output variable depending on the size and
duration of the system deviation. If the value for the integration time RESET is set to zero,
the controller works as a P or PD controller. The influence of the integral component on
the control loop increases when the value of the integration time is reduced.
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KH 8384-5 EN