Ge 4-9, User-set scaling – Rockwell Automation 1746-NR8 SLC 500 RTD/Resistance Input Module User Manual User Manual
Page 57
Publication 1746-UM003A-EN-P
Channel Configuration, Data, and Status 4-9
User-Set Scaling
Proportional Counts - If the user wants to configure the module to scale the
data word to something other than -32,768 to +32,767, the user defines what
the upper and lower limits are going to be. However, the maximum range
remains -32,768 to +32,767. The user defines what the upper and lower limits
are going to be by placing the range in the user-set scaling words for that
channel. 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 is configured for user-set scaling is
channel 3. As shown in the following illustration, the user has programmed the
channel 3 configuration word for 1000
Ω
potentiometer (bits 0 to 3):
proportional counts data format (bits 4 and 5): and configuration words 14
and 15 for scaling. The program for the following example is described on
page 5-4 in chapter 5.
The user desires 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 ohms) and 50 ft./minute (1000 ohms).
As shown in the illustration on below, the user selects a 1000
Ω
potentiometer
as the input type. If the user chooses engineering units as the data format, the
module data word is a value between 0 and 1000 ohms. However, if the user
chooses the proportional counts data format and utilizes the user-set scaling
feature, the number 3 can be entered in O:e.14 and the number 50 in O:e.15.
In this situation, the RTD module returns a number between 3 and 50 in its
data word. This action saves the user time in ladder programming.
Figure 4.4 User-set Scaling Using Proportional Counts Data Format
0
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
1
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
1
0
0
0
0
Selected Proportional Counts Data Format
Selected 1000
Ω
Pot
Channel 3
Configuration Word
O:e.3
Channel 3
Range
Lower scale limit set
for 3
Upper scale limit set
for 3
O:e.14
O:e.15