Rockwell Automation 1746-NR8 SLC 500 RTD/Resistance Input Module User Manual - Manual (Page 60)

Publication 1746-UM003A-EN-P
4-12 Channel Configuration, Data, and Status
Proportional Counts to Engineering Units
Equation:
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, S
LOW
= 0
Ω
and S
HIGH
= 1000
Ω
.
Solution:
Engineering Units to Proportional Counts
Equation:
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, S
LOW
= 0
Ω
and S
HIGH
= 3000
Ω
.
Solution:
The following table shows the temperature ranges of several 1746-NR8 RTDs.
The table applies to both 0.25 and 1.0 mA excitation currents. The
temperature ranges of the remaining RTDs vary with excitation current, for
example, 1000
Ω
Platinum 385, 1000
Ω
Platinum 3916
,
and 10
Ω
Copper 426.
Engr Units Equivalent SLOW SHIGH - SLOW
( )
Proportional Counts value displayed + 32768
( )
65536
------------------------------------------------------------------------------------------------------------------------- ×
 
 
 
+ =
Engr Units Equivalent 0
Ω
1000 ohms - 0 ohms
[ ]
21567 32768 +
( )
65536
-------------------------------------------- ×
 
 
 
826 ohms = + =
Proportional Counts Equivalent 65536
Engr Units desired - SLOW
( )
SHIGH - SLOW
( )
-------------------------------------------------------------------------- ×
 
 
 
- 32768 =
Prop. Counts = {65536 x [1809 ohms - 0 ohms]} -32768 = 6750