Convert 4-20 mA to 0-10 V, 1-5 V and 0-5 V

By Wu Peng, Senior Process Instrumentation Engineer · Last reviewed July 26, 2026

To convert 4-20 mA to 0-10 V you put the loop current through a precision resistor and read the voltage across it, or you use an active converter. A resistor alone cannot give you a true 0 V. Because 4 mA still has to drop something, 500 ohm turns 4-20 mA into 2-10 V, not 0-10 V. Only an active converter, or rescaling inside the controller, puts the zero back at 0 V.

That 2 V offset is 20 percent of a 0-10 V span. Miss it at commissioning and every reading sits 20 percent of span high at zero. Below: resistor values, the loop-compliance limit that decides whether 500 ohm is legal on your supply, NAMUR fault currents in volts, the reverse conversion, and the wiring practice that protects the signal.

Contents

• Two conversion methods
• Resistor values and voltages
• Why 0-10 V fails
• Loop compliance limits
• Input impedance error
• Fault levels in volts
• Converting voltage to current
• Wiring and safety
• Choosing the target range
• FAQ

Two conversion methods

A 4-20 mA loop carries information as current, and every receiver measures it the same way: the current runs through a known resistance and the input reads the voltage across it. The two methods differ only in what sits between loop and input.

Passive shunt (burden) resistor. One precision resistor in series with the loop, at the receiving device. It needs no power. It scales the signal but cannot shift it, so the output keeps the live zero: 1-5 V, 2-10 V or 0.4-2 V.

Active signal converter. A powered module that applies gain and offset, so it can produce a true 0-10 V or 0-5 V output, usually with galvanic isolation. Vendor data for DIN-rail isolators in this class quotes 0.2 percent accuracy, an input burden near 100 ohm and 4 kV isolation.

Resistor values and voltages

Ohm’s law does the whole job: V = I x R. ANSI/ISA-50.1-1982 (R1992) names 250 ohm as the standard load resistor and allows 50 to 1000 ohm, which is why 1-5 V is the classic voltage form of the signal.

Resistor	At 4 mA	At 12 mA	At 20 mA	Matches input
100 Ω	0.4 V	1.2 V	2.0 V	0-2 V cards, low-burden loops
150 Ω	0.6 V	1.8 V	3.0 V	3.3 V logic inputs
250 Ω	1.0 V	3.0 V	5.0 V	1-5 V and 0-5 V inputs (ISA standard value)
500 Ω	2.0 V	6.0 V	10.0 V	0-10 V inputs, with a 2 V live zero left in

Voltages are exact products of current and resistance. Real parts shift them slightly.

Match the resistor to the card range, not to habit. A 250 ohm burden on a 0-10 V input peaks at 5.000 V, so a channel scaled 0-10 V reports 50 percent at full sensor span: that reads like a failed transmitter, not a wrong resistor.

Two notes on the parts. 250 ohm and 500 ohm are not E96 values, so what you buy is 249 ohm and 499 ohm: at 20 mA those give 4.980 V and 9.980 V, 0.4 and 0.2 percent below nominal full scale. Put the difference into the controller’s scaling. P = I²R gives 0.10 W at 250 ohm and 0.20 W at 500 ohm, so 0.25 W is the minimum and 0.5 W leaves margin in a warm panel.

Why 0-10 V fails

A 4-20 mA signal has a live zero: zero process value is 4 mA, not 0 mA. A resistor multiplies, it does not subtract, so 4 mA always lands above zero volts. With 500 ohm it lands on exactly 2.000 V.

V = I x R = 0.004 A x 500 Ω = 2.0 V at zero process value

Scale that input as a plain 0-10 V channel and 0 percent of range is 0 V. True zero then reads 2/10 of full scale, 20 percent of span high. On a 0-300 psi transmitter, an empty line reads 60 psi. There are three options.

Option	What you do	When to use it
Rescale in the controller	Set 2.000 V as 0 percent, 10.000 V as 100 percent	Default when the card takes raw endpoints
Use an active converter	Gain 0.625 V/mA, offset −2.5 V: 4 mA gives 0.000 V, 20 mA gives 10.000 V	Fixed 0-10 V inputs, or when you need isolation too
Order a voltage output	Specify a native 0-10 V, 0-5 V or 1-5 V output instead of 4-20 mA	New instruments, short runs, test benches

Other targets: 0-5 V is 0.3125 V/mA with −1.25 V offset; 1-5 V is 0.25 V/mA and 2-10 V is 0.5 V/mA, both with zero offset. The two zero-offset ranges are exactly the ones a plain resistor can produce.

Loop compliance limits

Before choosing 500 ohm, check the loop can afford it. A 2-wire transmitter needs a minimum terminal voltage for its own electronics, typically 10.5 to 12 V; what is left pays for burden and wire.

R_max = (V_supply − V_{transmitter,min}) / 0.020 A

24 V supply, 12 V transmitter minimum: (24 − 12) / 0.020 = 600 Ω total loop resistance

Loop supply	Transmitter min	Resistance budget	Left for cable
12 V	10 V	100 Ω	None at 250 Ω; fit 100 Ω into a 0-2 V input
24 V	12 V	600 Ω	350 Ω at 250 Ω; only 100 Ω at 500 Ω
24 V	10.5 V	675 Ω	175 Ω at 500 Ω
30 V	12 V	900 Ω	400 Ω at 500 Ω, ample

The last column is what remains for cable, barriers, indicators and any other series device once the burden resistor is fitted.

This is where the popular “just fit 500 ohm” advice breaks. On a 24 V supply with a 12 V transmitter, a 500 ohm burden leaves 100 ohm for everything else. A 500 m run of 22 AWG copper, there and back, is already about 53 ohm at 20 degrees C, and copper rises roughly 0.4 percent per degree C, so a warm cable tray plus a loop indicator uses up the rest.

Run out of compliance and the reading pins short of 20 mA, which looks like a calibration problem and is not one. The 4-20 mA current loop guide works the budget through in detail.

Input impedance error

The burden resistor is never alone. The analog input sits across it, so the current sees the resistor in parallel with the card’s input impedance and the voltage comes out low.

R_effective = (R x Z_in) / (R + Z_in)

Datasheet numbers vary far more than the usual “100 kilohm or more” claim: the Allen-Bradley Micro820 specifies 14.14 kilohm on its 0-10 V analog inputs, and compact loggers can sit lower still.

500 Ω across a 14.14 kΩ input: R_effective = 482.9 Ω, so 20 mA reads 9.658 V instead of 10.000 V, 3.4 percent low

A 250 ohm burden on the same input gives 245.7 ohm and reads 1.7 percent low. Loading dominates the error budget, well above a 0.1 percent resistor tolerance, and it repeats. Two clean answers: take the input impedance from the datasheet and trim the burden value, or inject 4.000 mA and 20.000 mA with a loop calibrator and scale from what the controller reports. Percentages here are referenced to the true expected voltage.

Fault levels in volts

NAMUR NE43 defines the bands a smart transmitter uses to say it has failed rather than measured: valid signal 3.8 to 20.5 mA, downscale fault at 3.6 mA and below, upscale fault at 21.0 mA and above. Those thresholds have to survive the conversion, and that is the part no resistor table mentions.

NE43 level	Current	Across 250 Ω	Across 500 Ω
Downscale fault	3.6 mA and below	0.90 V	1.80 V
Start of valid range	3.8 mA	0.95 V	1.90 V
End of valid range	20.5 mA	5.13 V	10.25 V
Upscale fault	21.0 mA and above	5.25 V	10.50 V

Values are the products of the NE43 currents and the burden resistance.

Read the right-hand column against a 0-10 V input. An upscale fault at 21 mA wants 10.50 V, the card clips at 10 V, and a failed sensor arrives as a healthy full-scale reading. The 250 ohm column fits inside that card, and its downscale band at 0.90 V lets a “below 0.95 V” alarm catch a broken wire. A strict 0-5 V input clips 21 mA too, so drop to 150 ohm, or take diagnostics from the transmitter over HART.

Converting voltage to current

Going the other way, there is no passive option. A resistor can drop a current, but nothing can make one, and a 4-20 mA loop needs a source to push 4 mA at zero signal. Feeding a drive, an HMI analog output or a bench supply into a controller that only accepts current means an active V to I converter, powered from the receiving loop or its own 24 V supply.

I = 4 + 16 x (V − V_min) / (V_max − V_min)

6.25 V on a 0-10 V source: 4 + 16 x 0.625 = 14.0 mA

Two things to check on the way back. The converter output has to drive the receiving loop, so the compliance arithmetic now applies to its supply. And the live zero is manufactured by the converter: 0 V in gives 4 mA out, and a broken voltage cable gives 4 mA out as well, so the two look identical downstream and diagnostics have to come from the converter. The calculator runs this direction too.

Wiring and safety

Put the resistor at the receiving end, across the input terminals, and land the loop wires on the same two terminals. That keeps the cable run in current mode, where the noise immunity lives; a resistor at the transmitter end turns the run into low-level voltage transmission. Use twisted pair, shield grounded at one end.

Three field points worth checking.

• Single-ended inputs need a reference. The low side of the burden sits at the analog common of the card. If the loop is also grounded in the field, two grounds give you a circulating current: break one, or fit an isolator. A differential input tolerates more, up to its common-mode rating.
• Inserting a burden opens a live loop. While the terminal is open, everything downstream sees zero current and acts on it. Use test terminals with shorting links, or take the loop out of service first.
• Intrinsically safe loops need a documented change. An uncertified resistor in an IS loop changes the entity parameters the certification was granted on. Anything in the hazardous area, or behind a barrier, goes back to the loop drawing first.

One failure mode is worth designing against. If the burden resistor or its terminal goes open circuit, the transmitter drives its full compliance voltage into an input rated for 10 V; a resistor rated above the loop current, terminals that get retorqued and a card with input protection all help. Layouts for 2-wire, 3-wire and 4-wire devices are in the wiring guide.

Choosing the target range

Most of the pain here comes from taking 0-10 V as a given. If the input accepts more than one range, 1-5 V with a 250 ohm burden is the better target: lower burden, standard ISA value, fault bands inside the card range, and a live zero that still shows a broken wire.

Your situation	Do this
Card accepts 1-5 V or 0-5 V	249 Ω burden, scale 1.000-5.000 V, keep the live zero
Card is 0-10 V and rescalable	499 Ω burden, scale 2.000-10.000 V, check loop compliance first
Card is fixed 0-10 V	Active converter with gain 0.625 V/mA and offset −2.5 V
Ground potentials differ or the loop is shared	Isolating converter, whatever the range
Instrument not bought yet	Order the voltage output and skip the conversion

Two sizing notes go with that table. A card whose range is wider than the signal throws away resolution: 1-5 V on a 12-bit 0-10 V input leaves 1,638 of 4,095 counts, against 3,276 on a 0-5 V input, and the calculator lists the counts per combination. And whatever the range, specify the resistor as metal film, 0.1 percent, low temperature coefficient: a 25 ppm per degree C part drifts 0.075 percent over a 30 degree C panel swing, against 0.3 percent for a 100 ppm part.

The last row is the one buyers forget. Several of our sensors ship with voltage outputs as a factory option: the SI-390 industrial pressure transducer with 1-5 V or 0-10 V, the SI-303 low pressure transducer with 0-5 V or 1-5 V, and the SI-338 ceramic pressure sensor with 0-5 V or 0.5-4.5 V for OEM boards.

Long runs and classified areas keep 4-20 mA in the field and convert at the panel; the 4-20 mA pressure transmitters range covers that side. Run your numbers in the 4-20 mA to voltage calculator, or convert current to engineering units with the 4-20 mA calculator.

FAQ

How do you convert 4/20mA to 0-10V?

Two options. Put a 500 ohm precision resistor in the loop and rescale 2-10 V as 0-100 percent in the controller, or use an active converter with a gain of 0.625 V/mA and an offset of −2.5 V for a true 0-10 V. Check first that the loop supply can afford a 500 ohm burden.

Is 4/20mA the same as 0-10V?

No. Same information, different form. 4-20 mA is a current signal with a live zero: immune to cable voltage drop and able to signal a broken wire. 0-10 V has no live zero, suits short runs only, and cannot tell zero process value apart from a cut cable.

How to convert 4/20mA to voltage?

Pass the loop current through a known resistance and measure across it: V = I x R. 250 ohm gives 1-5 V, 500 ohm gives 2-10 V, 100 ohm gives 0.4-2 V. Mount it at the receiving device, use 0.1 percent metal film rated 0.25 W or more, and confirm the loop has compliance to spare.

What resistor converts 4-20mA to 2 10V?

500 ohm, since 0.004 A x 500 ohm is 2 V and 0.020 A x 500 ohm is 10 V. The E96 stock value is 499 ohm, which gives 1.996-9.980 V, about 0.2 percent low at full scale. Trim that in the controller scaling.

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Tell us what the receiving system accepts, how far the cable runs and whether the area is classified, and we configure the instrument and its output around that instead of leaving it to be corrected at the terminals. Reach our application engineers or use the form below.

Written and technically reviewed by Wu Peng and the Instranova engineering team.