# 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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### 18 thoughts on “Formula to Calculate 4-20 mA from Process Variable”

1. Thanks for sharing

2. usefull

3. for calculating mA, what is 6.25 value please explain

• Hello Mazhar, 100/(20-4) = 6.25

4. 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

5. 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.

6. Thanks for the clarification ?

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

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

9. % to MA

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

10. 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.

11. 1500*16=24000
24000/2500=9.6
9.6+4=13.6

12. 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

13. direct formula
1500/2500*16+4=13.6ma

14. 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