During calibration of a pressure sensor (4-20ma) I was unable to achieve an precise calibration 0 to 30.00 PSIA within 0.7 PSIA at the lower or upper range when using the scaling functions.
The sensor was calibrated from the manufacture within 0.1% accuracy.
I decided to check the Analog Input with a calibrated Fluke Processmeter from: 4.000 ma to 20.000ma.
The Hardware was configured for 4-20ma input and default scaling 0 to 8191 inputs with strong filtering enabled. Unilogic version 1.22.13
Here are the results:
Fluke(ma)
Actual Count
Expected Count
Count Diff.
4.0000
-45
0
-45
6.0000
954
1024
-70
8.0000
1954
2048
-94
12.0000
3953
4096
-143
14.0000
4957
5119
-162
16.0000
5951
6143
-192
18.0000
6951
7167
-216
20.0000
7949
8191
-242
The counts are non-linear corresponding to the 4-20ma inputs, i would expect the counts difference to be constant.
I was not able to check all the channels, but could this be just a bad channel or are the values within the specification of the AI card?