Rockwell Automation 1746-NR8 SLC 500 RTD/Resistance Input Module User Manual - Manual (Page 55)

Publication 1746-UM003A-EN-P
Channel Configuration, Data, and Status 4-7
Default scaling can be selected for scaled-for-PID data format and proportional
counts data format. User-set scaling can be defined for proportional counts data
format. For a description of default scaling, see page 4-7 (scaled-for-PID data
format) and page 4-8 (proportional counts data format). For a description of
user-set scaling using proportional counts data format, see page 4-9.
The equations on page 4-11 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 page 4-13 and page 4-14. 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 and 16383. Zero (0) corresponds
to the lowest temperature value of the RTD type or the lowest resistance value
(ohms). The value 16383 corresponds to the highest temperature value for that
RTD or the highest resistance value (ohms). For example, if a 100
Ω
Platinum
RTD (
α
= 0.003916) is selected, then the relationship of temperature and
module counts is:
The following illustration shows the linear relationship between output counts
and temperature when one uses scaled-or-PID data format.
Figure 4.2 Linear Relationship Between Temperature and PID Counts
Temperature Counts
-200°C 0
+630°C 16383
Counts
16383
°C
630°C -200°C