Sako SKI600, Manual

Page: 123 / 180

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of the regulating speed, which may result
in fluctuation. The regulating method is as
follows: set integral time a large value and
derivative time zero, use proportion regulation
alone to operate the system, check the steady
deviation (offset) of feedback signal and
reference when modifying the reference. If
the offset is in the same direction of reference
changing (for example, increase the reference,
and the feedback value is always smaller than
reference after the system became stable);
otherwise, decrease proportional gain and
repeat the process above until the offset
reaching a quite small value.
Integral time (Ti):
It determines the speed of integral regulation.
When feedback shows deviation with
reference, output regulation value increases
continuously. If the deviation exists
continuously, the regulation value will stay
increasing until no deviation. The integral
regulator can eliminate offset effectively,
but being too strong can result in repeating
overshoot and cause fluctuation to system.
The adjustment of integral time parameter
usually goes in descending order with
observation of the effect at the same time
until a steady speed fulfilling requirement is
reached.
Derivative time (Td):
It determines the adjustment intensity of
deviation changing rate.
When the deviation is changing, regulation
value in proportion to deviation changing rate
is output. This regulation value is only relevant
to the direction and value of deviation
change, not of the deviation itself. Derivative
F8.08
Sampling cycle T
0.01 ～ 100.00s
0.10
0.00: automatic
Sampling cycle corresponds to feedback.
Regulator operates once in every
sampling cycle. The longer of the cycle,
the slower of the response, but the better
of the suppress effect to interference
signal. Normally no need to set this
parameter.
F8.09
Error limit
0.0 ～ 100.0％
0.0%
Error limit is the ratio of deviation (feedback
and reference) absolute value to reference.
PID regulator stops operation when feedback
is within this range, as showed in the following
figure. Setting this parameter correctly is
helpful to improve the system stability, as
frequent adjustment around target value can
be avoided.
Fig. F8-3 Error Limit Schematic Diagram
3FGFSFODF
5JNF
&SSPS
-JNJU
5JNF
0VUQVU
'SFR
'FFECBDL
4.2 Detailed Function Description
regulation is processed according to variation
trend when feedback signal is changing so as
to suppress the change. Please be cautious
to use it, because it will amplify interference
of system easily, especially those whose
changing frequency is relatively high.