Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 111)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 111
Feedback and I/O Chapter 2
Square Root
The square root function can be applied to each analog input through the use of
P256 [Anlg In Sqrt]. Enable the function if the input signal varies with the square
of the quantity (for example drive speed) being controlled.
If the mode of the input is bipolar voltage (-10…10V), then the square root
function returns 0 for all negative voltages.
The function uses the square root of the analog value as compared to its full scale
(for example
) and multiplies it times the full scale of
what it controls (for example 60 Hz).
The complete function can be describes as follows:
Setting high and low values to 0V, 10V, 0 Hz, and 60 Hz, the expression reduces
to the following:
5V 0.5 or 50% and 0.5 0.707 = =
Analog Value - [Analog In x Lo]
[Analog In x Hi] - [Analog In x Lo]
-------------------------------------------------------------
⎝ ⎠
⎛ ⎞ (
Speed Ref A Hi
[ ] – [Speed Ref A Lo]
)
[Speed Ref A Lo] + ×
Analog Value
10V
------------------------
⎝ ⎠
⎛ ⎞ 60 Hz
Ч
10
9
8
7
6
5
4
3
2
1
0
0 1 2 3 4 5 6 7 8 9 10