Pid Function Block (Pid Controller) - Samson 3787 Mounting And Operating Instructions

7.4.3.2 PID Function Block (PID controller)

A PID Function Block includes the input channel processing, the PID control and the analog
output channel processing.
The configuration of the PID Block (PID controller) is dependent on each automation task.
Simple control loops, feedforward controls, cascade control and cascade control with limits
can be implemented in combination with a further controller block.
The following options exist for processing the measured variable within the PID Function
Block (PID controller):
Signal scaling, signal limits, control of the modes, feedforward control, limit control, alarm
detection and passing on the signal status.
The PID Block (PID controller) can be used for various automation strategies. The Block has a
flexible control algorithm which can be configured depending on the application.
The PID Block receives its set point depending on the operating mode (MODE_BLK) from the
CAS_IN, RCAS_IN or SP input variables. PV_SCALE, SP_HI_LIM, SP_LO_LIM, SP_RATE_UP
and SP_RATE_DN are used to form an internal operating set point.
The Block receives the actual value over the IN input variable. The process variable PV is
formed from this, 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, from the process variable PV (actual value) and from the system deviation.
The individual PID components are included in the calculation of the manipulated variable as
follows:
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-
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.
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 com-
ponent on the control loop increases when the value of the integration time is reduced.
Derivative component:
In controlled systems with long delay times, e.g. in temperature control loops, it makes
sense to use the derivative component RATE of the controller. Using the derivative compo-
Parameter description
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EB 8383-1 EN