Siemens SIMATIC S7-1200 Function Manual page 284

Instructions
9.1 PID_Compact
During controller tuning and in automatic mode, PID_Compact 1.0 is set to "Inactive"
operating mode under the following conditions:
● New mean value >= 1.1 x old mean value
● New mean value <= 0.9 x old mean value
● Current sampling time >= 1.5 x current mean value
● Current sampling time <= 0.5 x current mean value
Sampling time of the PID algorithm
The controlled system needs a certain amount of time to respond to changes in the output
value. It is therefore not advisable to calculate the output value in every cycle. The sampling
time of the PID algorithm represents the time between two calculations of the output value. It
is calculated during tuning and rounded to a multiple of the cycle time. All other functions of
PID_Compact are executed at every call.
PID algorithm
PID_Compact is a PIDT1 controller with anti-windup and weighting of the proportional and
derivative actions. The following equation is used to calculate the output value.
Symbol
y
K
p
s
b
w
x
T
I
a
c
284
Description
Output value
Proportional gain
Laplace operator
Proportional action weighting
Setpoint
Process value
Integral action time
Derivative delay coefficient (T1 = a × T
Derivative action time
Derivative action weighting
)
D
Function Manual, 03/2017, A5E35300227-AC
PID control