Rockwell Automation 1336E IMPACT Adjustable Frequency AC Drive User Manual V 1-4.XX - Manual (Page 121)

Setting Up the Input/Output 7-9
Figure 7.6
Example of Scaling and Offset for 4 – 20 mA Inputs
In this example, the 4 – 20 mA input is offset and scaled to provide
±2048 range from the 4 – 20 mA input. To do this, you would need to:
1. Compare the range of the output that you want to 4 – 20.
In the example shown in Figure 7.6, the ranges were the same, so
we used Step 3.
2. Calculate the offset.
3. Convert the mA range to a digital range, if you have not already
done so. Keep in mind that 20 mA equals 2048 and 4 mA equals
0.
4. Compare the output of the conversion to internal units to the
output range you want.
In the example shown in Figure 7.6, the ranges were different, so
we used Step 5.
5. Calculate the scale. In this example, the internal units were +2048
and you needed 4096; therefore, you would use a scale value of 2.
6. Enter the offset and scale values into the appropriate parameters.
4–20 mA
Input
Offset Scale
+20
+4
+20
+4
+2048
0
+4096
0
2 0
Analog to
Digital
Converter
20=2048
4=0
Drive Output
Range of the
input after the offset
is applied
Range of the
input in internal
drive units
4 – 20 mA Pot
A C B
By subtracting 0mA from
both 20 and 4, you main-
tain the current range,
with +4 as the zero point. By multiplying +2048 by2,
you get the +4096 range
you were looking for
.
If the ranges are: Then you: Go to:
The same (that is, both positive) Do not need an offset Step 3
Different Need an offset Step 2
If the values are: Then you: Go to:
Identical Do not need to scale the value Step 6
Different Need to scale the value Step 5