4-20 mA to Physical Value Conversion and Vice Versa

4-20 mA to Physical Value Conversion and Vice Versa is very important for calculating the physical value of pressure, temperature. Also, we will learn the conversion process of physical value to 4-20 mA.

Nowadays different types of Transmitters have their widespread applications in factories in place of usual Indicators.

All instruments operate from the BMS room (Building Management System). Therefore, it is not possible to visit the location and see the readings of various instruments like Pressure Gauge, Temperature Gauge. 

The transmitters are the devices that are used for transmitting the signals from a large distant place to the BMS room.

The transmitter transmits a signal in the range 4-20 mA or 0-10 V. mA stands for Milliampere and V stands for voltage.

In this article, we will learn how to convert transmitted signal 4-20 mA to physical Value (Pressure, Temperature, etc.)

4-20mA means the minimum current is 4 mA and the maximum current is 20 mA.

Formula to Convert mA to Physical value

Formula to Convert mA to Physical value

Formula to Convert Physical Value to mA

Formula to Convert Physical Value to mA

Physical Value can be anything such as Pressure, Temperature, etc. The mathematical procedure for conversion remains the same.

Pv   = Physical value corresponds to mA
I      = Current  value corresponds to Physical Value
Pvhigh    = Maximum range of physical value
Pvlow      = Minimum range of physical value
I high       = Maximum Current value
I Low       = Minimum Current value

How to Convert Physical value to 4-20 mA?

Let us take examples to understand the conversion process of physical quantity to 4-20 mA.

Example 1

Range: 0 to 150 bar                          
Output: 4 to 20 mA

Calculate Pressure for 12 mA

Formula to Convert mA to Physical value

Step 1 : Maximum range of pressure – minimum range of pressure
=150-0=150bar

Step 2  : Output current – minimum range of Current
=12 – 4 = 8 mA

Step 3  : Max mA – Min mA
= 20-4=16mA

Step 4  : Min Pressure
= 0 bar

Pressure = (150/16) * 8 + 0
= 75 bar

Calculate Current for 100 bar

Step 1     : Max mA – Min mA
= 20-4=16mA

Step 2       : Applied pressure – minimum range of pressure
=100-0=100 bar

Step 3       : Maximum range of pressure – minimum range of pressure
=150-0=150bar

Step 4       : Min mA
= 4mA

I (mA) = (16/150) *100 + 4
= 14.67mA

pressure to mA conversion

Example 2

Range  : -50 to 50 mbar                            
Output : 4 to 20 mA

Calculate current for – 25mbar

Step 1       : Max mA – Min mA
= 20-4=16mA

Step 2       : Applied pressure – minimum range of pressure
= -25 – (- 50) = 25 mbar

Step 3       : Maximum range of pressure – minimum range of pressure
= 50 – (-50) =100 mbar

Step 4       : Min mA
= 4mA

I (mA) =   (16/100) *25 + 4
=   8 mA

Calculate Pressure for 12 mA

Step 1       : Maximum range of pressure – minimum range of pressure
= 50-(-50)=100 mbar

Step 2       : Output current – minimum range of Current
=12 – 4 = 8 mA

Step 3       : Max mA – Min mA
= 20-4=16mA

Step 4       :   Min Pressure
= -50 mbar

Pressure =   (100/16) *8 + (-50)
= 0 mbar

pressure to mA conversion

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