Home » Formula to Calculate 4-20 mA from Process Variable

Formula to Calculate 4-20 mA from Process Variable

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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16 comments

Gunjan Raval August 29, 2016 at 3:56 pm

Thanks for sharing

Noor Mustafa August 30, 2016 at 7:21 pm

usefull

Mazhar October 19, 2016 at 7:28 am

for calculating mA, what is 6.25 value please explain

S Bharadwaj Reddy October 20, 2016 at 1:17 am

Hello Mazhar, 100/(20-4) = 6.25

Hashim November 22, 2016 at 4:11 pm

Dear can You explain correctly how 6.25 came. While we are dividing 100/(20-4) it’s not showing 6.25

S Bharadwaj Reddy November 23, 2016 at 4:07 am

Hi, 100/(20-4) = 100/16 = 6.25

Etuk Victor January 30, 2017 at 10:47 am

Very good formula, but how did u derive or get the +25

S Bharadwaj Reddy January 30, 2017 at 12:58 pm

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.

Etuk Victor January 30, 2017 at 4:01 pm

Thanks for the clarification ?

Ray April 8, 2017 at 3:57 pm

Another simple formula for converting Percentage into equivalent 4-20mA current,
4-20mA = (percentage*16)+ 4
Example : 60%*16+4=13.6

Danish September 25, 2017 at 4:09 pm

how 60%+25/6.25=13.6mA,,please answer me

S Bharadwaj Reddy September 25, 2017 at 4:12 pm

Hi, Please see brackets, (60+25)/6.25 = 85/6.25 = 13.6

muhammad imran ali September 28, 2017 at 6:35 am

please check formala
% to MA

%= 60
how much MA at 60%
so
60/6.25+4= 13.6

Jagan ch September 29, 2017 at 2:54 pm

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.

keenam Augustine January 24, 2020 at 9:18 am

1500*16=24000
24000/2500=9.6
9.6+4=13.6

Mubeen February 7, 2020 at 1:02 pm

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

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