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4-20mA Formulas and Examples

4-20 mA transmitter current output can be converted to the voltage within a specified range, from 0 to a maximal amplitude Vmax, as shown in the following picture:

4-20ma-formulas-and-examples

 

 Calling I the output current and V the Voltage—or other physical variables (PV) —between Vmin (which is usually 0) and Vmax; the conversion formulas are as follows:

 

  • I [mA] = ( ( (V − Vmin) / ( Vmax − Vmin) ) × 16 ) + 4

  • V [Voltage] = ( (I − 4 ) / 16) × ( Vmax − Vmin ) + Vmin

  • PV [units] = ( (I − 4 ) / 16) × ( PVmax − PVmin ) + PVmin

Where,

I is the current,

V is the voltage,

PV is the Process Variable

min is the Lower Range Value of the respective signal

max is the Upper Range Value of the respective signal

Note that the values and units of min and max are units must be same.

Example 1 :

A Analog output card gives an output voltage of 2.5V and its overall range is 0-5V. calculate the equivalent 4-20mA current value.

I =  ( ( (VVmin) / ( VmaxVmin) ) × 16 ) + 4

I =  ( ( (2.5 − 0) / ( 5 − 0) ) × 16 ) + 4

I = 12 mA

Example 2 :

A transmitter output range is 13.5mA and its output range is 4-20mA. Calculate equivalent voltage. consider 0-10V is the output voltage range.

V = ( (I − 4 ) / 16) × ( VmaxVmin ) + Vmin

V = ((13.5 – 4)/16 x (10 – 0 ) + 0

V = 5.9375 V

Example 3 :

A Flow transmitters output current is 16.5mA and its range is 0-1500 m3/hr. Calculate the equivalent flow rate value.

PV = ( (I − 4 ) / 16) × ( PVmaxPVmin ) + PVmin

PV = ( (16.5 − 4 ) / 16) × ( 1500 − ) + 0

PV = 1171.87 m3/hr

Also Read : 4-20mA Transmitter Principle

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12 comments

shajib September 10, 2016 at 5:41 pm

Thanx, Realy it is important for me.

Reply
kingsley September 14, 2016 at 2:49 pm

Thanks very much sir, this is very important.

pls how do i print it.

Reply
jee October 16, 2016 at 5:26 pm

formula wrong ex: range -50 to 50 psi i get 12 mA what is the pv value?

Reply
S Bharadwaj Reddy October 16, 2016 at 10:46 pm

Hi Balajee, Formula Working fine. Please see : PV = [ (12-4)/16 X { 50- (-50) } ] + (-50) = ( 0.5 X 100 ) – 50 = 0. Also Click Here to Use online Calculator for fast calculations.

Reply
balaji October 17, 2016 at 5:05 pm

yes Mr S Bharadwaj reddy its by mistake. Thanks 4 reply

Reply
mohammed hafez November 26, 2016 at 8:10 am

I(mA)=16/(Vmax-Vmin)(V-Vmin)+4Vmax/(Vmax-Vmin)

Reply
Kartik lad August 4, 2017 at 6:07 pm

0 psi

Reply
Khuram meHar November 26, 2016 at 8:06 pm

How amazing very good effort.

Reply
omar April 7, 2017 at 6:34 am

thanks

Reply
prasad anrak August 7, 2017 at 9:31 am

thank you brother

Reply
sudhesh katare September 15, 2017 at 2:52 pm

how to calculate the % of valve opening at milli ampere 4 to 20

Reply
S Bharadwaj Reddy September 15, 2017 at 3:17 pm

Hi, For 4-20mA to 0 – 100 % Conversion : CLICK HERE

Reply

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