Rockwell Automation 1336E IMPACT Adjustable Frequency AC Drive User Manual V 1-4.XX User Manual
Page 119
Setting Up the Input/Output
7-7
Determining the offset and scale parameters for analog outputs can be
confusing. You need to calculate the offset before you can calculate
the scale. However, because the drive applies the scale first and then
the offset, you need to take the inverse of your results. For example, if
you calculated a scale factor of 2 and you were trying to convert from
±4096 drive units to a ±10V output, you would actually want to use a
scale factor of 1/2, or 0.5.
Figure 7.5 shows an example of the scale and offset values for an
analog output parameter.
Figure 7.5
Example of Scale and Offset for Analog Outputs
Figure 7.5 is used to help explain the offset and scale values for
analog output. To determine the offset and scale values, you need to:
1. Compare the output range to the internal units range. In the
example shown in Figure 7.5, you would compare the ranges
represented by A and B.
In the example shown in Figure 7.5, the ranges were different so
we used Step 2.
2. Calculate the offset. For example, if you need a 0 to +10V input
and you have a
±4096 internal range, you need to offset the 0 to
+10V range to get a
± range. In this case, you would have an
offset of -5.
3. Take the opposite sign of what your offset calculations show. In
this case, the true offset would be +5. Therefore, when +5 is
added to the range values after the range is converted to an analog
value, the range comes out to 0 to 10V.
Analog
Output
Offset
Scale
+10
0
+5
–5
+1024
–1024
+4096
–4096
0.25
+5
0
0
5
Digital to
Analog
Converter
±1024 =
±5V
Internal
Units
Range of the drive
output in internal
units after the scale
is applied
Range of the analog
output before the
offset is applied
Add drive
A
C
B
By adding +5 to both
±5, you get the 0–10V
range your meter requires.
By multiplying
±4096 by 0.25,
you get
±1024 which, when
converted, equals
±5V.
5V
0V
10V
If the ranges are:
Then you:
Go to:
The same (that is, both
±,
both 0 to +n, or both 0 to -n)
Do not need an offset
Different
Need an offset