Proportional counts to engineering units, Engineering units to proportional counts – Rockwell Automation 1746-NR8 SLC 500 RTD/Resistance Input Module User Manual User 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