4-20mA to Process Variable Formula


#1

This current to measurement conversion tool will convert an electrical signal within the range of 4 to 20 milliamps to the ideal reading of any linear measurement type and create an incremental milliamp conversion scale for each measurement range entered.

Formula

This tool uses the following formula to calculate the the measurement reading output from a current signal input over a 4-20mA range:

Measurement Rdg = Low Limit + (High Limit – Low Limit) x (mA out -4) / 16

Parameters

Current Loop Signal (4-20mA) Reading

Add the current loop signal reading in milliamps (mA) between 4 and 20 mA that you want to convert.

Measurement Unit

Enter the measurement unit associated with the output values.

Lowest Measurement

Add the minimum possible value for the measurement range of your instrument. For example zero would be a typical value for most instrumentation but you can also add negative (-) or positive (+) values as well. A value in any engineering units can be used as long as it relates to a linear measurement, and the same unit is used for the Highest value.

Highest Measurement

Add the maximum possible value for the measurement range of your instrument, e.g. full scale or full range. This value can be negative (-) or positive (+). Any engineering units can be used as long as it relates to a linear measurement, but the same unit must be used for the Lowest value.

Measurement Reading – Answer

This is the ideal converted measurement for your instrument and therefore represents a perfect reading excluding the measurement uncertainty error of your instrument. The answer value is displayed in the same engineering unit that you entered for the Lowest and Highest range points.

Help

Conversion precision

How precise is the converted measurement?
The linear measurement Answer is displayed to a precision of 9 significant figures.

Inverted signal

How do I convert an inverted or reversed 4-20mA signal?
Swap around the values you enter into the Lowest and Highest text boxes

Calibrating 4-20mA device

Can I use this converter to calibrate a 4-20mA measurement device?
You can partly use this converter to aid calibration. When you calibrate you will need to precisely measure both the input and output parameter. You can use this converter to determine the ideal measurement reading and compare it with the calibration measurement to determine the calibration error.

Input or output 4-20mA

Do I enter the input or the output value for the 4-20mA signal?
This converter is not input or output specific, so you can convert either ‘input to output’ or ‘output to input’.

Linear measurement

What is a linear measurement?
This means that if you were to plot input and output readings on a graph they would produce a straight line.