Rockwell Automation 1746-NR4 SLC RTD/Resistance Input Module User Manual - Manual (Page 79)

Publication 1746-UM008B-EN-P - December 2006
Channel Configuration, Data, and Status 79
User-set Scaling
Proportional Counts - The second case to consider is User-set Scaling
using proportional counts when the scaling select bits 13 and 14 are
set to 01 or 10. Here you can configure the module to scale the data
word to something other than -32,768 to 32,767. However, the
maximum range remains -32,768 to +32,767. You define what the
upper and lower limits are going to be by placing the range in the
user-set scaling words for range 0 (words 4 and 5) or range 1 (words 6
and 7). The module scales the input data to the upper and lower limit
in an linear relationship. The following example clarifies this feature.
In this example, the RTD module channel that will be configured for
user-set scaling is channel 3.
As shown in User-set Scaling Using Proportional Counts Data Format
on page 80, you have programmed the channel 3 configuration word
for 1000
Ω potentiometer (bits 0…3): proportional counts data format
(bits 4 and 5): and configuration words 4 and 5 for scaling (bits 13 and
14).
The program for the following example is described on page 95 in
Chapter 6.
EXAMPLE
You desire to control the line speed of a conveyor. A
1000
Ω potentiometer is used to sense the conveyor
line speed. The line speed varies between 3
ft/minute (0
Ω) and 50 ft/minute (1000 Ω).
As shown in User-set Scaling Using Proportional
Counts Data Format on page 80, you select a 1000
Ω
potentiometer as the input type.
If you choose engineering units as the data format,
the module data word is a value between 0…1000
Ω.
However, if you choose the proportional counts data
format and utilizes the user-set scaling feature, the
number 3 can be entered in O:e.4 and the number
50 in O:e.5. In this situation, the RTD module returns
a number between 3…50 in its data word. This
action saves you time in ladder programming.