Cleveland Motion Controls Quantum Tension Controller REV A - Manual (Page 28)

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5.0 Menu PID
5.4 PID Menu
Principle
The P.I.D. is the heart of the controller calculation system when using the Closed loop mode.
P , I , and D parameters are the coefficients which give the actual output result from the
Measurement - Set point difference .
CAUTION : the PID calculation must be disabled during the machine rest periods to avoid that
a static Measurement - Set point difference increases the output value to the maximum (giving
a very high overshoot for the next machine restart) .
The following process has obviously to be managed by the global machine management system
! (using the external switches Reg and Init) .
How does it work
There are two options for the PID calculation principle :Fixed PID (coefficients) or Variable PID
(coefficients) which have to be chosen in the PID Menu (" click in the box " choice mode) .
The Variable PID option is very useful when the Fixed PID is unable to keep the same stability
level for the whole range of the Web diameter variation .
The Variable PID option offers to define a P, I and D specific value for the min. diameter, and a
different one for the max. diameter . the three P, I, and D parameters will be automatically
updated in relation to a diameter measurement input (linear variation between min. and max.
for each parameter)
P parameter: This parameter is the direct gain on the Measurement - Set point difference .
The P coefficient will directly affect the global system response time .
CAUTION : The higher the value, the higher the response time, but with a lower stability .
I parameter: This parameter is used to cancel the " static error " by the accumulation of this
error from the beginning, and by adding this error to the set point until reaching the equality .
When the Measurement - Set point difference becomes null, the Integral value is stabilized.
A high coefficient value will make the system more reactif by decreasing the time for the
Measure to reach the Set point actual value .
D parameter: This parameter is used to help the system to react for fast transients.
It is generally only used for the Dancer applications, in order to stabilize the dancer position
when the web speed is variable .
CAUTION : this parameter is used for react to transients, but it means that it could be highly
sensitive to the electric interferences on the measurement signal .Be very careful to connect the
wiring shields at the best .
Process
The PID calculation is managed by the external switches Reg and Init.
Init Reg PID calcul mode
0 0 Stopped (blocked)
1 0 initialisation
0 1 processing
1 1 processing
CAUTION : when using the diameter calculation (counters inputs), the initialisation of diameter
calculation is managed by the same external switches (Reg = 0 , Init = 1)