Rockwell Automation 1762-IR4 RTD/Resistance Input Module - Manual (Page 45)

Publication 1762-UM003A-EN-P - February 2003
Module Data, Status, and Channel Configuration 3-11
Figure 3.1 Linear Relationship Between Temperature and Proportional Counts
The value +32767 corresponds to the highest value for the device. For
example, if a 100
Ω
platinum 385 RTD is selected, the lowest
temperature of -200
°
C corresponds to -32768 counts. The highest
temperature of 850
°
C corresponds to +32767 counts. See Determining
Effective Resolution and Range on page 3-20.
Scaling Examples
+ 32,767
-32,768
850 ˚C
±200 ˚C
Counts
°C
EXAMPLE
Scaled-for-PID to Engineering Units x1
•
input type = 200
Ω
Platinum RTD
• α
= 0.00385°C
•
range = -200 to +850°C S
LOW
= -200°C S
HIGH
= +850°C
•
channel data = 3421(scaled-for-PID)
Engineering Units Equivalent = S
LOW
+ (S
HIGH
- S
LOW
) x (channel data/16383)]
Engineering Units Equivalent = -200°C + [(+850°C -(-200°C)) x (3421/16383)] =
19.25°C