Calculate the equivalent 4-20mA signal from Porcess 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 m^{3}/hr

Lower Range Value, LRV = 0 m^{3}/hr

Upper Range Value, URV = 2500 m^{3}/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.

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