Rockwell Automation 1791-XXXX ANALOG BLOCK I/O - Manual (Page 15)

Introducing Block I/O
Chapter 1
1-8
User Scaling
User scaling is available only when using the block transfer mode. This
mode allows you to define S
max
and S
min
in engineering units in the block
transfer write data table. The integer range is 32,767 to –32,768.
Important: If the range of user scaling values is set less than the range of
binary counts scaling values, input resolution is sacrificed.
Scaling Example
Using the +10V range scale, the following illustration shows five possible
input signals.
14 Bits
13.96 Bits
Nominal Range
10.25 10 0 -10 -10.25
Resolution
Input Signal
Margin Margin
The following table shows how the five signals will be scaled using each
of the three scaling methods. In the user scaling column, the S
max
was set
to represent 5000 and the S
min
was set to represent 0.
I t V l
Scaling Method
Input Value
Binary Counts Default User
Approx. +10.25V 8395 10250 5062
+10.000V 8191 10000 5000 (Smax)
0.000V 0000 00000 2500
-10.000V -8192 -10000 0000 (Smin)
Approx. -10.25V -8396 -10250 -0062
The type of output your block I/O module has depends on its catalog
number:
1791-N4V2 and 1791-NDV have two +10V voltage outputs
1791-N4C2 and 1791-NDC have two 0-20mA current outputs
For any of the above modules, if your program tries to write a value which
is outside the output range, the output will be clamped at either the
maximum or minimum value. This condition will be indicated in the block
transfer read status word.
Outputs