VLT
®
Series 3500
66
★ = ROM default setting. ✔ = Normal Danfoss setup. Text in ( ) = display text. Figures in [ ] are used when communicating with the bus.
120 Control Range (CONTRL RAN)
Value:
0 to 100% ★ 100%
Function:
The regulator range (bandwidth) limits the output from the
PID controller as a % of f
MAX
.
Description of choice:
A desired % value of f
MAX
can be selected. If the regulator
range is reduced, speed variations will become smaller dur-
ing initial adjustment.
121 Proportional Gain (PROPRT/L G)
Value:
00.00 to 10.00 ★ 00.01
Function:
The proportional gain sets the amplification factor of the er-
ror (the difference between the feedback signal and the
setpoint).
Description of choice:
Quick regulation is obtained at a high amplification, but if
the amplification is too high, the process may become un-
stable due to overshoot.
122 Integral Time (INTEGRAL T)
Value:
OFF to 9999.99 sec. ★ OFF
Function:
The integral time determines how long the PID controller
takes to correct the fault. The integral time results in a delay
of the signal, and therefore has a dampening effect that will
improve stability.
Description of choice:
Quick regulation is obtained through a short integral time.
However, if this time is set too short, the process will be-
come unstable. If the integral time is set long, regulation
becomes unnecessarily slow.
Off
means that the function is
inactive.
123 Differential Time (DIFFERENTL)
Value:
OFF to 10.00 sec. ★ OFF
Function:
Quick control is obtained by a short differentiation time. If
this time is too short, the process may become unstable.
When the differentiation time is set at 0 sec., the differential
function is not active.
Description of choice:
In typical pump and fan systems, the differential function is
not used.
124 Lowpass Filter (LOWPASS FI)
Value:
00.0 to 10.00 sec. ★ 00.0 sec.
Function:
The feedback signal is dampened by means of a lowpass
filter with a time constant (τ) of 0-10 sec. When set for 00.0
seconds, the lowpass filter is deactivated.
Description of choice:
If a time constant (τ) is programmed to be 0.1 sec., the cut-
off frequency for the lowpass filter will be 1/0.1 = 10 Hz.
The PID controller will then regulate a feedback signal
which varies at a frequency of less than 10 Hz. If the feed-
back signal varies at a higher frequency than 10 Hz, the
PID controller will not react.
125 Feedback Factor (FEEDBACK F)
Value:
0 to 500% ★ 100%
Function:
The feedback factor is used if the transmitter cannot be se-
lected optimally for the scale range of the setpoint.
Description of choice:
A value can be programmed which scales the feedback sig-
nal to fit it to the desired setpoint. If 50% is used as
setpoint, for example, and the feedback signal is only 25%,
parameter 125 enables programming of 200%, which
means that the feedback signal is recorded as 50% (25% x
200% = 50%).
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