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Input Processing
Input Processing
The input signal to IN is filtered through a lag filter whose time constant is set in
PV_FTIME, and then set as the process variable (PV).
Setpoint (SP) Limiters
The path for computing the SP differs depending on the mode. In Cas mode, CAS_IN is
used for SP. In RCas mode, RCAS_IN is used for SP. If the value of CAS_IN or
RCAS_IN, whichever is used, is greater than SP_HI_LIM (high limit) or less than
SP_LO_LIM (low limit), the internal SP is set to the respective limits. When the target
mode is Auto or Man, and when SP-PV tracking is not specified at the same time, the
rate of change in the setpoint is also limited (by the values of SP_RATE_UP and
SP_RATE_DN).
PID Computation
For PID control, the block employs the PV-proportional and PV-derivative type PID
control algorithm (referred to as the I-PD control algorithm) for Auto and RCas mode.
This algorithm measures control stability against sudden changes in the setpoint, such
as when you enter a new setpoint value. At the same time, the IPD algorithm ensures
excellent controllability by performing proportional, integral, and derivative control
actions in response to changes of characteristics in the controlled process, changes in
load, and occurrences of disturbances.
For Cas mode, PV-derivative type PID control algorithm (referred to as the PI-D control
algorithm) is employed in order to obtain better performance against the changes in the
setpoint.
The algorithm is automatically changed by the block according to the mode. A basic
form of each algorithm is expressed in the equation below.
In Auto / RCas mode
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PID Function Block
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