Rockwell Automation 1746-NI8 SLC 500 Analog Input Modules User Manual - Manual (Page 51)

5–10 Channel Configuration, Data, and Status
Publication 1746Ć6.8 - April 1997
1746-NI4 Data Format Units to “Real” Units
Situation: A transducer is being used to measure flow rate.
The –10V dc to +10V dc signal is proportional to 0–100 GPM.
The channel data word is in 1746-NI4 data format.
The channel data = 10000.
Find: “Real” units equivalent in GPM.
Equation:
Real Units Equivalent + channel data value
ǒ
S
HIGH
* S
LOW
input range
Ǔ
where: S
LOW
= 0 GPM
S
HIGH
= 100 GPM
channel data word = 5500
NI4 full scale default value (from table on page 5–6) = 65535
Solution:
Real Units Equivalent + 10000
ǒ
100 GPM * 0 GPM
65535
Ǔ
+ 15.26 GPM
User Defined Limits Data Format to “Real” Units
Situation: A transducer is being used to measure pressure.
The –10V dc to +10V dc signal is proportional to 0–200 psi.
The channel data word is in user defined data format.
The lower scale limit (configuration word 8) = 0.
The upper scale limit (configuration word 9) = 20000.
The channel data word = 16600.
Find: “Real” units equivalent in psi.
Equation:
Real Units Equivalent + channel data word
ƪ
(S
HIGH
* S
LOW
)
ǒupper scale limit * lower scale limitǓ
ƫ
where: S
LOW
= 0 psi
S
HIGH
= 200 psi
Solution:
Real Units Equivalent + 16600
ƪ
ǒ200 psi * 0 psiǓ
(20000 * 0)
ƫ
+ 166.00 psi