Siemens Simatic S7-1500 - Properties; Properties of the CPU Part

Principles for control
2.3 Characteristic values of the control section
PID control
Function Manual, 03/2017, A5E35300227-AC
21
The controllability of the controlled system can be estimated based on the ratio T
u
/T
g
, or T
u
×
v
max
/X
max
. Rule:
Process type
T
u
/ T
g
Suitability of the controlled system for controlling
I
< 0,1
can be controlled well
II 0.1 to 0.3 can still be controlled
III
> 0,3
difficult to control
Influence of the dead time on the controllability of a controlled system
A controlled system with dead time and recovery reacts as follows to a jump of the output
value.
T
t
Dead time
T
u
Delay time
T
g
Recovery time
y
Output value
x
Process value
The controllability of a self-regulating controlled system with dead time is determined by the
ratio of T
t
to T
g
. T
t
must be small compared to T
g
. Rule:
T
t
/T
g
≤ 1