Set the signal type and the range of the instrument, then type any one of the signal, the percent, the real value or the PLC counts. The others fill in. Example: a 4-20 mA level transmitter on a 22 ft tank reads 12 mA at 50%, which is 11 ft.

1. The instrument range

Signal type Signal at 0% mA Signal at 100% mA Real value at 0% Real value at 100% Unit label (ft, psi, gpm, °F...) Relationship

2. Convert

Type in any box. The others update.

Signal mA Percent % Real value ft PLC counts

Counts scale Counts at 0% Counts at 100%

Points along the range

Percent	Signal	Value	Counts

The same point in every signal type

Useful for matching a 0-10 V input to a 4-20 mA output, or the other way around.

Signal type	At this point

Loop resistor (mA to volts)

A precision resistor turns a current loop into a voltage. 250 ohms turns 4-20 mA into 1-5 V.

Current mA Resistor Ω Voltage V

Loop power check

Does the supply have enough voltage at 20 mA?

Supply V Transmitter minimum V Receiver resistance Ω

Tank level to pressure

For a pressure transmitter at the bottom of an open tank. Use this to find the pressure range to set for the tank height.

Liquid height Height unit Specific gravity (water = 1)

How the 4-20 mA converter works

A 4-20 mA transmitter sends its reading as a current. Zero percent of the range is 4 mA and 100 percent is 20 mA, so the signal is a straight line between them. Tell the tool the range of the instrument (for example 0 to 22 feet), then type any one of the signal, the percent, the real value or the PLC counts and the rest fill in. It also handles 0-20 mA, 0-10 V, 1-5 V, 0-5 V, 2-10 V, custom ranges and square-root flow signals.

Steps

Choose the signal type. The 0% and 100% signal boxes fill in, and you can edit them for a custom range.
Enter the real range of the instrument, such as 0 and 22 with the unit ft.
Type in any box: the signal in mA or V, the percent, the real value, or the PLC counts. The other three update.
Use the table for common points, the signal-type table to match a 0-10 V input to a 4-20 mA output, and the loop tools to check a resistor or loop power.

Example

A 22 ft tank with a 4-20 mA level transmitter: 4 mA is 0 ft, 12 mA is 50% or 11 ft, 16 mA is 75% or 16.5 ft, and 20 mA is 22 ft. The span is 16 mA, so each foot is about 0.727 mA. The formula is mA = 4 + 16 x (percent / 100).

Questions

How do I convert mA to percent?: Subtract 4 and divide by 16. For example, 12 mA gives (12 - 4) / 16 = 50%. For a 0-20 mA signal, divide by 20.
How do I find the mA for a level in a tank?: Divide the level by the full range to get the fraction, then mA = 4 + 16 x fraction. At 11 ft in a 22 ft tank the fraction is 0.5, so the signal is 12 mA.
What does the square-root setting do?: Flow measured with a differential pressure transmitter is proportional to the square root of the pressure signal. With square root on, 50% signal is about 70.7% of full flow.
Why does 4 mA mean zero?: A live zero means a reading of 0% still carries current. If the loop reads 0 mA, the wire is probably broken, so a fault looks different from a real zero.
What are PLC counts?: An analog input card turns the signal into a whole number. Many cards use 0 to 27648 for the span of the range, others use 6400 to 32000 or 0 to 32767. Pick the scale your card uses, or enter your own.
Does it work offline?: Yes. It runs in your browser and nothing is sent anywhere.

4-20 mA converter