Samson 3730-5 - PID Function Block

17.2.7 PID Function Block
A PID Function Block contains the input channel processing, the proportional-integral-deriva
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tive (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 manipulate variable feedforwarding, cascade con
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trol and cascade controls with limitation in combination with another controller function
block can be implemented.
The following options are available for processing the measured variable within the PID
Function Block (PID controller): Signal scaling and limiting, mode control, feedforward con
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trol, limit control, 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
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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 operating set point.
The block receives the actual 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 manipulated variable is calculated from the set
point value SP and the process variable PV (actual value) resulting from the system deviation.
The individual PID components are included in the calculation of the manipulated 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 (actual value). The manipulated variable is changed by the propor
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tional factor GAIN. This change corresponds to the system deviation multiplied by the
gain factor. If a controller works only with a proportional component, the control loop
has a permanent system deviation.
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Integral component:
The system deviation resulting from the calculation of the manipulated variable using the
proportional component is integrated over the integral component of the controller until it
is negligible. The integral function corrects the manipulated 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 compo
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nent on the control loop increases when the value of the integration time is reduced.
116 EB 8384-5 EN
Appendix