What Is a 1-5 VDC Signal and When Should You Use It?

A 1-5 VDC signal is an analog output where 1 V represents the zero or lowest reading and 5 V represents the full-scale reading. It is the voltage twin of the 4-20 mA current loop: run 4-20 mA through a 250-ohm resistor and you get exactly 1-5 V. Choose 1-5 VDC when your receiver (PLC analog card, data logger, or OEM controller) expects a voltage input, the cable run is short, and the electrical environment is reasonably clean. Choose 4-20 mA instead when the cable is long, noise is heavy, or you need to power the transmitter over the same two wires.

How the 1-5 VDC scale works

The "live zero" at 1 V is the key feature. Because zero pressure is represented by 1 V rather than 0 V, a broken wire or dead transmitter that drops the signal to 0 V is distinguishable from a true zero reading. That diagnostic gap is the same reason 4-20 mA uses 4 mA as its zero.

The conversion is linear, so any intermediate value maps directly: voltage = 1 + (pressure fraction × 4).

1-5 VDC vs. 4-20 mA

Both carry the same information; the difference is how they behave over wire.

• Noise immunity. A current loop is largely immune to induced noise and voltage drop because the same current flows through the entire loop. A voltage signal loses accuracy as cable resistance and electrical noise add to or subtract from the reading.
• Distance. 4-20 mA is the standard choice for long runs in plant environments. 1-5 VDC is best kept to short runs, typically within a panel or between nearby equipment.
• Wiring. A 4-20 mA transmitter usually needs only two wires and can be loop-powered. A voltage-output transmitter generally needs a separate supply plus signal and common conductors.
• Receiver compatibility. Many PLC analog input cards, data loggers, and OEM boards accept 1-5 V directly, which avoids adding a dropping resistor.

1-5 VDC vs. 0-5 VDC and 0-10 VDC

• 0-5 VDC has no live zero, so an open wire reads the same as a true zero. It is common in low-cost sensors and some legacy equipment.
• 0-10 VDC doubles the span and is widely used in building controls (HVAC, damper and valve actuators). It offers more resolution per volt than 0-5 V but still lacks a live zero.
• 1-5 VDC keeps the live-zero diagnostic and matches the 4-20 mA world through a simple 250-ohm resistor, which makes it convenient when a current transmitter must feed a voltage input.

Typical applications

• PLC analog input modules that specify a 1-5 V range
• Data loggers and chart recorders with voltage inputs
• OEM equipment where the controller board expects 1-5 V
• Retrofits where an existing 4-20 mA loop is terminated with a 250-ohm resistor to feed a voltage card

BEC Controls offers 1-5 VDC alongside 4-20 mA, 0-5 VDC, 0-10 VDC, 0-100 mV, 0.5-4.5 VDC, and custom outputs on its differential, gauge, and vacuum pressure transmitters, with pressure ranges from 0.5" WC to 1500 PSI.

Selection factors

Before specifying 1-5 VDC, confirm:

1. Receiver input range — does the PLC card, logger, or controller accept 1-5 V directly, or will you need a resistor and a current output instead?
2. Cable length — short runs favor voltage; long runs favor 4-20 mA.
3. Electrical noise — motors, drives, and switching equipment nearby push you toward a current loop.
4. Wiring architecture — voltage output needs a supply plus signal conductors; a loop-powered 4-20 mA device may need only two wires.
5. Diagnostics — if you need to detect an open wire, the 1 V live zero (or 4 mA) gives you that; 0-5 V and 0-10 V do not.

If your answer to most of these points toward a short, clean, voltage-input installation, 1-5 VDC is the straightforward choice. If distance or noise dominates, specify 4-20 mA and convert at the receiver with a 250-ohm resistor if the input card requires voltage.