Last Updated on August 5, 2022 by Electricalvolt

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 calculation.

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 Physical Value to mA**

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

P_{v } = Physical value corresponds to mA

I_{ } = Current_{ }value corresponds to Physical Value

P_{vhigh } = Maximum range of physical value

P_{vlow }= 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*

*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*

*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**

**Example 2**

Range : -50 to 50 mbar

Output : 4 to 20 mA

*Calculate current for – 25mbar*

*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*

*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**

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