The formula for calculating equivalent current (ma) from known process variable (PV), Lower range value (LRV) and Upper range value (URV).
The formula is:
SPAN = URV – LRV
Where
PV = Process Variable
LRV = Low Range Value
URV = Upper Range Value
mA = milli ampere
Consider left side of formula for Process variable, LRV of transmitter lower range, Span is the difference between LRV & URV of transmitter ranges.
Consider right side of formula for current (ma), LRV of standard current range .i.e is 4ma,
Span is the difference between LRV (4ma) & URV (20ma) of standard current range
.i.e. 20 – 4 = 16, Using this formula we can calculate mA from pv and as well as pv from mA.