Rockwell Automation 1746-NR4 SLC RTD/Resistance Input Module User Manual - Manual (Page 68)

Publication 1746-UM008B-EN-P - December 2006
68 Channel Configuration, Data, and Status
Using Scaled-for-PID and Proportional Counts Formats
The RTD module provides eight options for displaying input channel
data. These are 0.1 °F, 0.1 °C, 1 °F, 1 °C, 0.1
Ω, 1 Ω, Scaled-for-PID,
and Proportional Counts. The first six options represent real
engineering units and do not require explanation. The Scaled-for-PID
selection allows you to directly interface RTD Data into a PID
instruction without intermediate scale operations. The Proportional
Counts selection provides the highest display resolution, but also
require you to manually convert the channel data to real Engineering
Units.
Default scaling can be selected for scaled-for-PID data format and
proportional counts data format. User-set scaling can be selected for
proportional counts data format.
For a description of default scaling, see Scaled–for–PID and
Proportional Counts Data Format. For a description of user-set scaling
using proportional counts data format, see page 67.
The equations on page 71 show how to convert from Scaled-for-PID
to Engineering Units, Engineering Units to Scaled-for-PID,
Proportional Counts to Engineering Units, and Engineering Units to
Proportional Counts.
To perform the conversions, you must know the defined temperature
or resistance range for the channel’s input type.
Refer to the Channel Data Word Format in the tables on pages 72…73.
The lowest possible value for an input type is S
LOW
, and the highest
possible value is S
HIGH
.
Scaled–for–PID
If the user selects scaled–for–PID as the data format, the data word for
that channel is a number between 0…16,383. Zero (0) corresponds to
the lowest temperature value of the RTD type or the lowest resistance
value (ohms). The value 16,383 corresponds to the highest
temperature value for that RTD or the highest resistance value (ohms).
For example, if a 100
Ω Platinum RTD (a = 0.003916) is selected, then
the relationship of temperature and module counts is shown in the
following table.
Relationship Between Temperature and Counts
Temperature Counts
-200 °C (-328 °F) 0
+630 °C (1166 °F) 16383