4-20 mA vs. 0-10 V: Which Analog Signal Should You Use?

4–20 mA and 0–10 V are the two most common analog signals in industrial control. Both carry a measurement, such as level, pressure, temperature or speed, as a continuously varying value. 4–20 mA is the better choice for long runs and noisy plants; 0–10 V is simpler and fine for short runs inside a panel.

Comparison

Why current loops travel well

In a current loop the transmitter regulates the current, and current is the same everywhere in a series circuit. Wire resistance does not change the reading, as long as the supply has enough voltage to drive the loop. Induced noise also has a much smaller effect on a low-impedance current loop than on a high-impedance voltage input.

The "live zero"

Starting at 4 mA rather than 0 means the bottom of the range is still a real, measurable current. If a wire breaks or a transmitter dies, the current falls to 0 mA, which the PLC can flag as a fault. Many instruments also signal faults outside the normal range (the NAMUR NE 43 recommendation uses below 3.6 mA or above 21 mA). The 4 mA also gives a 2-wire transmitter enough current to power itself from the loop.

When 0–10 V makes sense

• Short runs inside one control panel.
• Setting a VFD's speed reference from a nearby PLC.
• HVAC dampers, valves and controllers that are designed around 0–10 V.
• When several devices need to read the same signal (parallel connection is easy).

Scaling the signal in a PLC

The PLC converts the analog input into a raw number, and you scale it to engineering units:

Value = Min + (mA − 4) ÷ 16 × (Max − Min)

Example: a level transmitter ranged 0–300 cm reading 12 mA gives 0 + (12 − 4) ÷ 16 × 300 = 150 cm. For 0–10 V: Value = Min + V ÷ 10 × (Max − Min).

Converting between them

• A precision 250 Ω resistor across a voltage input turns 4–20 mA into 1–5 V.
• Signal conditioners convert and isolate between current and voltage, and also break ground loops.

Wiring tips

• Use twisted, shielded pair. Ground the shield at one end only, usually the panel end.
• Keep analog cables away from VFD motor leads and power wiring.
• Check whether the transmitter is 2-wire (loop-powered), 3-wire or 4-wire, and whether the PLC input supplies loop power.
• Match the input type in PLC configuration (current or voltage, and the range).

Products that output both

Many sensors come in either version. HTM's M18 ultrasonic sensors, for example, are offered with 4–20 mA or 0–10 V analog outputs plus a switching output. On the PLC side, modules such as the Unitronics IO-AI8 add analog inputs to Vision controllers. See also how ultrasonic sensors work.

Frequently asked questions

Is 4–20 mA more accurate than 0–10 V?
Not inherently, but it stays accurate over long, noisy cable runs where 0–10 V degrades.

What about 0–20 mA?
It exists but lacks the live zero, so you lose broken-wire detection. 4–20 mA is far more common.

Can I connect a 4–20 mA sensor to a 0–10 V input?
Only with a conversion resistor or signal converter, and only within the input's range. A 500 Ω resistor gives 2–10 V.

Need analog I/O or sensors?

Browse Unitronics I/O and HTM ultrasonic sensors, call 1-800-724-4209, or request a quote.