Operating instructions

NOTE
Always set the desired for par. 20-14 Maximum
Reference/Feedb. before setting the values for the PID
controller in parameter group 20-9*.
20-94 PID Integral Time
Range: Function:
20.00
s
*
[0.01 -
10000.00 s]
Over time, the integrator accumulates a
contribution to the output from the PID
controller as long as there is a deviation
between the Reference/Setpoint and
feedback signals. The contribution is propor-
tional to the size of the deviation. This ensures
that the deviation (error) approaches zero.
Quick response on any deviation is obtained
when the integral time is set to a low value.
Setting it too low, however, may cause the
control to become unstable.
The value set, is the time needed for the
integrator to add the same contribution as
the proportional part for a certain deviation.
If the value is set to 10,000, the controller will
act as a pure proportional controller with a P-
band based on the value set in par. 20-93 PID
Proportional Gain. When no deviation is
present, the output from the proportional
controller will be 0.
20-95 PID Differentiation Time
Range: Function:
0.00
s
*
[0.00 -
10.00 s]
The differentiator monitors the rate of change of
the feedback. If the feedback is changing quickly,
it will adjust the output of the PID Controller to
reduce the rate of change of the feedback. Quick
PID Controller response is obtained when this
value is large. However, if too large of a value is
used, the frequency converter’s output frequency
may become unstable.
Differentiation time is useful is situations where
extremely fast frequency converter response and
precise speed control are required. It can be
difficult to adjust this for proper system control.
Differentiation time is not commonly used in VLT
HVAC Drive applications. Therefore, it is generally
best to leave this parameter at 0 or OFF.
20-96 PID Diff. Gain Limit
Range: Function:
5.0 * [1.0 -
50.0 ]
The differential function of a PID Controller
responds to the rate of change of the feedback. As
a result, an abrupt change in the feedback can
cause the differential function to make a very large
change in the PID Controller’s output. This parame-
ter limits the maximum effect that the PID Control-
ler’s differential function can produce. A smaller
value reduces the maximum effect of the PID
Controller’s differential function.
This parameter is only active when par. 20-95 PID
Differentiation Time is not set to OFF (0 s).
Parameter Description
VLT
®
HVAC Drive Programming Guide
MG.11.CA.02 - VLT
®
is a registered Danfoss trademark 131
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