Forming The Error - Siemens SIMATIC Manual

Example of Process Value Normalization
If you want to enter the setpoint as a percentage, and you have a temperature
range of -20 to 85 °C applied to CRP_IN, you must normalize the temperature
range as a percentage.
The schematic below shows an example of adapting the temperature range
-20 to 85 °C to an internal scale of 0 to 100 %:
PV_NORM [%]
-20

Forming the Error

The difference between the setpoint and process value is the error before the
deadband.
The setpoint and process value must exist in the same unit.
Deadband (DEADB_W)
To suppress a small constant oscillation due to the manipulated variable
quantization (for example in pulse duration modulation with PULSEGEN) a
deadband (DEADBAND) is applied to the error. If DEADB_W = 0.0, the deadband
is deactivated. The effective error is indicated by the ER parameter.
ER = (SP_INT - PV) + DEAD_W
PID Temperature Control
A5E00125039-02
Continuous Temperature Controller FB 58 "TCONT_CP"
100
75
50
25
PV_OFFS = 0-0.9524*(-20)
= 19.05
20 40
PV_FAC = 100/(85-(-20))
= 0.9524
60 80 85 CRP_IN
ER
ER = (SP_INT - PV) - DEAD_W
DEADB_W
[°c]
SP_INT - PV
2-3