What are 0–10 V and 4–20 mA signals?

0–10 V and 4–20 mA are two analog signal ranges that carry a measurement or control command as an electrical value. A PLC, controller or drive converts the signal into pressure, temperature, level or a speed reference. Both carry continuously variable values, unlike digital on/off inputs.

0–10 V: the information is carried by voltage

A 0–10 V sensor represents its measurement as the voltage between the signal terminal and a defined reference terminal. With linear, increasing scaling, 0 V represents the lower limit and 10 V the upper limit. For a pressure sensor configured for 0–10 bar, 5 V means 5 bar. If the lower limit is −20 °C, however, 0 V means −20 °C: zero volts does not always mean a zero physical value.

4–20 mA: the information is carried by current

A 4–20 mA sensor carries information as the current flowing in its loop. 4 mA represents the lower limit and 20 mA the upper limit, giving a 16 mA measurement span. For the same 0–10 bar example, 12 mA means 5 bar. The 4 mA “live zero” maintains current at the bottom of the measurement range. A two-wire, loop-powered transmitter can also use this current to power its electronics; not every 4–20 mA device is a two-wire instrument.

How do the two signals represent the same value?

The demonstration repeats 0% → 25% → 50% → 75% → 100%; Stop returns to the initial 50% view. Reduced-motion preferences select a static display. This is ideal linear scale mapping, without cable-loss or interference calculations. For a drive configured with a 0–50 Hz reference range, 5 V or 12 mA commands 25 Hz. Actual motor speed also depends on the motor and load conditions.

General linear scaling: X = Xmin + [(S − Smin) / (Smax − Smin)] × (Xmax − Xmin), where S is the signal value. The fraction is V/10 for 0–10 V and (I − 4)/16 for 4–20 mA, with I expressed in mA. Set the units and limits correctly in the analog input/output configuration.

Which is preferable: 0–10 V or 4–20 mA?

0–10 V is useful for compatible devices connected by short, suitably routed cables, including a potentiometer speed reference. Reference potential differences, input impedance and cable conditions can affect the reading.

4–20 mA is generally advantageous for long field cables and environments with electromagnetic interference. However, it is not completely immune to interference; noise immunity also depends on routing, shielding and instrument design. It is not inherently more accurate, lower in power consumption or dependent on thicker cable. Follow the manufacturer's instructions for grounding and signal-reference connections.

Does a current loop have a cable limit?

Yes. The transmitter maintains its commanded current through the cable and receiver resistance only while sufficient voltage headroom remains. In an ideal example with a 24 V supply and a transmitter requiring at least 12 V, the total series-load allowance at 20 mA is (24 − 12) / 0.020 = 600 Ω. This includes cable and receiver resistance. Allow for supply tolerance, other voltage drops, fault current and design margin: 600 Ω is not a universal device limit.

Zero current, currents above 20 mA and fault reporting

4 mA is the normal lower measurement endpoint; 0 mA is not a normal 0% reading. Zero current may indicate an open loop, lost power or a connection problem; it does not uniquely identify the cause. Devices supporting NE 43 behaviour may use ≤3.6 mA or ≥21 mA for fault reporting. 20 mA is the upper endpoint of the normal measurement range, not an absolute physical current limit. A PID or PLC program should distinguish faults and overrange conditions from normal measurements.

Can one signal be converted to the other?

A suitable signal converter can perform the conversion. A 250 Ω measurement resistor produces 1–5 V from 4–20 mA, rather than 0–10 V. Check whether the receiver already contains this resistor, its tolerance and the additional loop load. The input ADC resolution alone does not establish overall system accuracy.

Does the 20 mA endpoint guarantee electrical safety?

No. Signal current and possible current through a person's body are different considerations. Voltage, contact path, duration, isolation and fault conditions matter. A 4–20 mA connection cannot be declared harmless simply from its signal range. Follow the instrument's electrical safety requirements for connection and measurement. Check active/passive current interfaces and loop power before making connections.