Rockwell Automation 1746-INT4 Thermocouple/MV Isolated/ User Manual - Manual (Page 49)

Publication 1746-UM614B-EN-P - September 2007
Channel Configuration, Data, and Status 49
Select the Correct Data Format
To provide the highest display resolution, select Scaled-for-PID or
Proportional Counts. To use either one, you may have to convert
channel data to/from Engineering Units, manually or logically.
The following examples show you how to do this.
Use Scaled-for-PID and Proportional Counts
You must obtain the minimum (S
LOW
) and maximum (S
HIGH
) values
of the temperature or millivolt range for the channel’s input type, and
use them in your computations.
We present these values in the section Using Channel Data Words on
page 51, in the table Format of a Channel Data Word.
Scaling Examples: Convert Between Units
Convert from Scaled-for-PID to Equivalent Engineering Units in °C
Equation: Engr Units Equivalent =
S
LOW
+ [(S
HIGH
– S
LOW
) x (Scaled-for-PID value displayed / 16,384)]
Assume type J input type, scaled-for-PID, channel data = 3421.
From Channel Data Word Format table, S
LOW
= –210 °C and S
HIGH
= 760 °C.
Solution: Engr Units Equivalent = -210 °C + [(760 °C – (-210 °C)) x (3421 / 16,384)] = -7.46 °C
Convert from Engineering Units in °C to Equivalent Scaled-for-PID Count
Equation: Scaled-for-PID Equivalent =
16,384 x [(Engineering Units desired – S
LOW
) / (S
HIGH
– S
LOW
]
Assume type J input type, scaled-for-PID, desired channel temp. = 344 °C.
From Channel Data Word Format table, S
LOW
= –210 °C and S
HIGH
= 760 °C.
Solution: Scaled-for-PID Equivalent = 16,384 x [(344 °C – (-210 °C)) / (760 °C – (-210 °C))] = 9357.
Convert from Proportional Counts to Equivalent Engineering Units in °F
Equation: Engr Units Equivalent = S
LOW
+ [(S
HIGH
– S
LOW
) x [(Proportional Counts value displayed + 32,768) / 65,536]]
Assume type E input type, proportional counts, channel data = 21,567 counts.
From Channel Data Word Format table, S
LOW
= –454 °F and S
HIGH
= 1832 °F.
Solution: Engr Units Equivalent = -454 °F + [[1832 °F – (-454 °F)] x [(21,567 + 32,768) / 65,536]] = 1441.3 °F
Convert from Engineering Units in °F to Equivalent Proportional Counts
Equation: Proportional Counts Equivalent = {65,536 x [(Engineering Units desired – S
LOW
) / (S
HIGH
– S
LOW
)]} – 32,768
Assume type E input type, proportional counts, desired channel temp. = 1000 °F.
From Channel Data Word Format table, S
LOW
= -454 °F and S
HIGH
= 1832 °F.
Solution: Proportional Counts Equivalent = {65,536 x [(1000 °F – (-454 °F)) / (1832 °F – (-454 °F))]} – 32,768 = 8916 counts.