How to Calculate 4-20mA current loop from Process Variable value of a field transmitter. Check the formula to find out equivalent 4-20mA signal from Process Variable.
Calculate 4-20mA from Process Variable
Formula :
First calculate equivalent percentage from the process variable
Percentage = ( X – LRV / URV – LRV ) . 100
Then calculate equivalent 4-20mA signal from percentage
4-20mA = ( Percentage + 25 ) / 6.25
Where,
X is Process Variable
LRV is Lower Range value
URV is Upper Range Value
Example:
A Flow transmitter has a range of 0 to 2500 m3/hr and it is displaying flow rate of 1500 m3/hr. calculate the transmitter output current.
Process variable = 1500 m3/hr
Lower Range Value, LRV = 0 m3/hr
Upper Range Value, URV = 2500 m3/hr
Note: units must be same for process variable, LRV & URV
Percentage = (1 500 – 0 / 2500 – 0 ) . 100 = 60 %
4-20 mA Signal = (Percentage + 25) / 6.25 = (60 + 25) / 6.25 = 13.6 mA
Also you can use online Instrumentation Calculator for Automatic calculations. Click Here.
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Thanks for sharing
usefull
for calculating mA, what is 6.25 value please explain
Hello Mazhar, 100/(20-4) = 6.25
Dear can You explain correctly how 6.25 came. While we are dividing 100/(20-4) it’s not showing 6.25
Hi, 100/(20-4) = 100/16 = 6.25
Very good formula, but how did u derive or get the +25
Hi, Percentage range is 0 to 100 i.e. starting from zero and current range is 4 to 20 i.e. starting from 4. Thats why we added 25 there. In order to get clear picture, try to calculate equivalent mA value for 0% with & without 25 in the formula.
Thanks for the clarification ?
Another simple formula for converting Percentage into equivalent 4-20mA current,
4-20mA = (percentage*16)+ 4
Example : 60%*16+4=13.6
how 60%+25/6.25=13.6mA,,please answer me
Hi, Please see brackets, (60+25)/6.25 = 85/6.25 = 13.6
please check formala
% to MA
%= 60
how much MA at 60%
so
60/6.25+4= 13.6
have a one dought about a soot blowing control valve calibartion. Today I done calibartion but it is not full closed valve passing when a giving 0 commond.it is passing 5kg pressure what can I do? Please tell me a prosedure.
1500*16=24000
24000/2500=9.6
9.6+4=13.6
What is the problem in this calculation…. For 20mA reading is 2500, then for x mA reading is 1500, We calculate x=20*1500/2500= 12mA… What am I missing here
direct formula
1500/2500*16+4=13.6ma
The LRV (lower range value) will usually be 0 for flows and pressures but not for load cells, drum levels, temperatures, etc.
For example, a -80C freezer may have a temperature transmitter calibrated from -100C to 20C. Formula 1 becomes useful. If the freezer temperature is -70C then what is the ma output from the transmitter?
First, find the transmitter span.
Span is URV – LRV or 20 – (-100) = 120C. Remember SPAN is always ONE number and RANGE is always TWO numbers.
Use the formula at the top to find the percentage:
(-70 – (-100)) / 120 = 30 / 120 = .25 or 25%.
To find the current use one of the formulas above or : (.25 x 16) + 4 = 8 ma