West Control Solutions N8840 - Manual (Page 25)

3.7 Second PID parameter set
The process characteristic is frequently affected by various factors such as
process value, correcting variable and material differences.
To comply with these requirements, the 8840 profiler can be switched over
between two parameter sets.
Parameter sets PArA and PAr.2 are provided for heating and cooling.
Dependent of configuration ( ConF/LOG/Pid.2), switch-over to the second
parameter set ( ConF/LOG/Pid.2) is via one of digital inputs di1, di2, di3,
key è or interface (OPTION).
g
Self-tuning is always done using the active parameter set, i.e. the second
parameter set must be active for optimizing.
Operation
8840 profiler 25 Second PID parameter set
Parameter adjustment effects
Parameter Control Line-out of disturbances Start-up behaviour
Pb1 higher increased damping slower line-out slower reduction of duty cycle
lower reduced damping faster line-out faster reduction of duty cycle
td1 higher reduced damping faster response to disturbances faster reduction of duty cycle
lower increased damping slower response to disturbances slower reduction of duty cycle
ti1 higher increased damping slower line-out slower reduction of duty cycle
lower reduced damping faster line-out faster reduction of duty cycle
Formulas
K = Vmax * Tu controller behavior Pb1 [phy. units] td1 [s] ti1 [s]
With 2-point and
3-point controllers,
the cycle time must be
adjusted to
t1 / t2 ≤ 0,25 * Tu
PID 1,7 * K 2 * Tu 2 * Tu
PD 0,5 * K Tu OFF
PI 2,6 * K OFF 6 * Tu
P K OFF OFF
3-point-stepping 1,7 * K Tu 2 * Tu