For any unit conversion on any PLC, you can use four function math with the following for PLC Analog Input Conversion Formula, which assumes integer math, as follows :
Formulas:
DataOffset = Data in input register at 4 mA (or zero analog signal of whatever range – for example 0 VDC on a 0-10 VDC transmitter)
DataSPan = Data at 20 mA – Data @ 4 mA
FACTOR = arbitrary factor (multiple of 10) needed to get proper resolution and accuracy
EU = Engineering Units x FACTOR
EUOffset = Engineering Units @ 4 mA x FACTOR
EUSpan = (Engineering Units @ 20 mA – Engineering Units @ 4 mA) x FACTOR
DATA = Actual data reading in input register
Note: PLC raw counts may vary from system to system.
0-60 psig from 4-20 mA with resolution of 0.1 psig:
FACTOR = 10
Data @ 4 mA = 6240
Data @ 20 mA = 31208
DataOffset = 6240
DataSpan = 31208 – 6240 = 24968
EUOffset = 0 x 10 = 0
EUSpan = (60 – 0) x 10 = 600
DATA = 18975
EU = ((EUSpan x (DATA – DataOffset))/DataSpan) + EUOffset
EU = ((600 x (18975 – 6240)) / 24968) + 0 = 306
ProcessValue = EU / FACTOR
Process Value = 306 / 10 = 30.6 psig
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