User Manual

PID is easy
Easy Book
170 Manual, 03/2014, A5E02486774-AF
PID algorithm
The PID (Proportional/Integral/Derivative) controller measures the time interval between two
calls and then evaluates the results for monitoring the sampling time. A mean value of the
sampling time is generated at each mode changeover and during initial startup. This value is
used as reference for the monitoring function and is used for calculation. Monitoring includes
the current measuring time between two calls and the mean value of the defined controller
sampling time.
The output value for the PID controller consists of three components:
● P (proportional): When calculated with the "P" component, the output value is proportional
to the difference between the setpoint and the process value (input value).
● I (integral): When calculated with the "I" component, the output value increases in
proportion to the duration of the difference between the setpoint and the process value
(input value) to finally correct the difference.
● D (derivative): When calculated with the "D" component, the output value increases as a
function of the increasing rate of change of the difference between the setpoint and the
process value (input value). The output value is corrected to the setpoint as quickly as
possible.
The PID controller uses the following formula to calculate the output value for the
PID_Compact instruction.
y
Output value
x
Process value
w
Setpoint value
s
Laplace operator
K
p
Proportional gain
(P component)
a Derivative delay coefficient
(D component)
T
1
Integral action time
(I component)
b Proportional action weighting
(P component)
T
D
Derivative action time
(D component)
c Derivative action weighting
(D component)
The PID controller uses the following formula to calculate the output value for the PID_3Step
instruction.
y
Output value
x
Process value
w
Setpoint value
s
Laplace operator
K
p
Proportional gain
(P component)
a Derivative delay coefficient
(D component)
T
1
Integral action time
(I component)
b Proportional action weighting
(P component)
T
D
Derivative action time
(D component)
c Derivative action weighting
(D component)