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.
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
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
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