The difference between the setpoint and process variable is the error signal. To suppress
a small constant oscillation due to the manipulated variable quantization (for example in
pulse duration modulation with PULSEGEN), a dead band is applied to the error signal
(DEADBAND). If DEADB_W = 0, the dead band is switched off.
The PID algorithm operates as a position algorithm. The proportional, integral (INT), and
derivative (DIF) actions are connected in parallel and can be activated or deactivated
individually. This allows P, PI, PD, and PID controllers to be configured. Pure I and D con-
trollers are also possible.
It is possible to switch over between a manual and an automatic mode. In the manual
mode, the manipulated variable is corrected to a manually selected value. The integrator
(INT) is set internally to LMN - LMN_P - DISV and the derivative unit (DIF) to 0 and
matched internally. This means that a switchover to the automatic mode does not cause
any sudden change in the manipulated value.
The manipulated value can be limited to a selected value using the LMNLIMIT function.
Signaling bits indicate when a limit is exceeded by the input variable. The LMN_NORM
function normalizes the output of LMNLIMIT according to the following formula:
LMN_FAC has the default 1 and LMN_OFF the default 0.
The manipulated value is also available in the peripheral format. The CRP_OUT function
converts the floating-point value LMN to a peripheral value according to the following for-
mula:
A disturbance variable can be fed forward at the DISV input.
Complete Restart/Restart
n FB 41 CONT_C has a complete restart routine that is run through when the input
parameter COM_RST = TRUE is set.
n During startup, the integrator is set internally to the initialization value I_ITVAL. When
it is called in a cyclic interrupt priority class, it then continues to work starting at this
value.
n All other outputs are set to their default values.
The block does not check for errors, so no error Information is output.
Error Signal
PID Algorithm
Manual Value
Manipulated Value
Feedforward Control
Modes
Error Information
VIPA SPEED7
Standard
PID Control > FB 41 - CONT_C - Continuous control
HB00 | OPL_SP7 | Operation list | en | 18-30 840
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