Flowrate %
mA
Figure 22 - 4-20 mA profile
Original 4-20 mA profile
Scaling factor of 0.5
Scaling factor of 1.5
The 4-20 mA profile is a linear relationship where y=mx+c the scaling factor alters the
gradient m. The speed limit function in control settings will also scale the analog signal.
The difference between scaling factor and speed limit is that the speed limit is a global
variable applied in all modes. The speed limit cannot exceed the high flow rate set point
(B).
The speed limit function takes precedence over the scaling factor. For example if the
qdos20 4-20 mA profile is 0 % flow at 4 mA to 100 % flow at 20 mA and a speed limit of
33 rpm is applied, followed by a scaling factor of 0.5, then the output will be 30 %. If a
scaling factor of 2 is applied in the same scenario then the output will be 33 rpm or 60 %,
as the speed limit takes precedence over the scaling factor.
If you are using manual scaling it is recommended to not use speed limit to avoid
confusion.
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