Rockwell Automation 1746-NR4 SLC RTD/Resistance Input Module User Manual - Manual (Page 71)

Publication 1746-UM008B-EN-P - December 2006
Channel Configuration, Data, and Status 71
Scaling Examples
The following examples are using the default scaling ranges.
Scaled-for-PID to Engineering Units
Equation Engr Units Equivalent = S
LOW
+ [(S
HIGH
- S
LOW
) x (Scaled-for-PID value displayed / 16383)]
Assume that the input type is an RTD, Platinum (200
Ω, a = 0.00385 °C, range = -200 °C…850 °C),
scaled-for-PID display type. Channel data = 3421.
Want to calculate °C equivalent.
From Channel Data Word Format (Table Data Formats for RTD Temperature Ranges for 0.5 and 2.0 mA
Excitation Current through Table Data Format for 500
Ω Resistance Input), S
LOW
= -200 °C and S
HIGH
= 850 °C.
Solution Engr Units Equivalent = -200 °C + [(850 °C - (-200 °C)) x (3421 / 16383)] = 19.25 °C.
Engineering Units to Scaled-for-PID
Equation Scaled-for-PID Equivalent = 16383 x [(Engineering Units desired - S
LOW
) / (S
HIGH
- S
LOW
)]
Assume that the input type is an RTD, Platinum (200 Ω, a = 0.00385 °C, range = -200 °C…850 °C),
scaled-for-PID display type. Desired channel temp. = 344 °C.
Want to calculate Scaled-for-PID equivalent.
From Channel Data Word Format (Table Data Formats for RTD Temperature Ranges for 0.5 and 2.0 mA
Excitation Current through Table Data Format for 500
Ω Resistance Input), S
LOW
= -200 °C and S
HIGH
= 850 °C.
Solution Scaled-for-PID Equivalent = 16383 x [(344 °C - (-200 °C)) / (850 °C - (-200 °C))] = 8488.
Proportional Counts to Engineering Units
Equation Engr Units Equivalent = S
LOW
+ {(S
HIGH
- S
LOW
) x [(Proportional Counts value displayed + 32768) / 65536]}
Assume that input type is a potentiometer (1000 Ω, range = 0 to 1000 Ω), proportional counts display type.
Channel data = 21567.
Want to calculate ohms equivalent.
From Channel Data Word Format (Table Data Formats for RTD Temperature Ranges for 0.5 and 2.0 mA
Excitation Current through Table Data Format for 500
Ω Resistance Input), S
LOW
= 0
Ω and S
HIGH
= 1000
Ω
Solution Engr Units Equivalent = 0
Ω + {[1000Ω - (0 Ω)] x [(21567 + 32768) / 65536]} = 829 Ω.
Engineering Units to Proportional Counts
Equation Proportional Counts Equivalent = {65536 x [(Engineering Units desired - S
LOW
) / (S
HIGH
- S
LOW
)]} - 32768
Assume that input type is a potentiometer (3000 Ω, range = 0 to 3000 Ω), proportional counts display type.
Desired channel resistance value = 1809 Ω.
Want to calculate Proportional Counts equivalent.
From Channel Data Word Format (Table Data Formats for RTD Temperature Ranges for 0.5 and 2.0 mA Excitation
Current through Table Data Format for 500
Ω Resistance Input), S
LOW
= 0
Ω and S
HIGH
= 3000
Ω.
Solution Proportional Counts Equivalent = {65536 x [(1809 Ω - (0 Ω)) / (3000 Ω- (0Ω))]} - 32768 = 6750.