An analog proximity sensor does not simply report "object detected" or "not detected" the way a normal digital sensor does. Instead it provides a continuous output signal — voltage or current — that varies according to the distance between the sensor and the target.
How it works
The sensing principle is the same as a standard inductive sensor: a coil and oscillator generate an electromagnetic field, and a metal target damps it by inducing eddy currents. The difference is what happens next.
A digital sensor compares the damping against a fixed threshold and outputs on or off. An analog sensor instead measures how much damping is occurring and converts that into a proportional output. Closer target, more damping, different output value — continuously, across the whole working window.
The two output standards
| 0–10 V DC | 4–20 mA | |
|---|---|---|
| Signal type | Voltage | Current |
| Cable length | Short runs only | Very long runs |
| Noise immunity | Moderate | Excellent |
| Broken cable detected? | No — 0 V is a valid reading | Yes — 0 mA is impossible in a healthy loop |
| Wiring | 3-wire | 2-wire loop possible |
| Typical use | Inside one panel or machine | Across a plant, near drives and motors |
Why 4–20 mA resists noise
A voltage signal degrades along a cable: conductor resistance produces a drop that appears directly as measurement error, and nearby motors and variable-frequency drives couple interference straight into the reading.
A current loop has neither weakness. The same current flows at every point in the loop regardless of cable length or resistance, and current signals are far less susceptible to induced noise. That is why process instrumentation standardised on 4–20 mA decades ago and has never moved away from it.
The diagnostic benefit is often overlooked. Because a healthy 4–20 mA loop never reads below 4 mA, a reading of 0 mA can only mean a broken cable or a dead sensor. With a 0–10 V sensor, 0 V is a perfectly valid measurement — so you cannot distinguish a genuine reading from a failure.
What you can do with an analog sensor
- Gap measurement — verify clearance between two components during assembly.
- Runout and eccentricity — monitor a rotating shaft for wear or misalignment.
- Thickness verification — confirm material thickness passing a fixed reference.
- Position control — close a control loop around actual position rather than end-stop switches.
- Wear monitoring — trend a measurement over time and schedule maintenance before failure.
Understanding the working window
Our analog sensors are linear across an 8–15 mm window. Below 8 mm and above 15 mm the output saturates and no longer represents distance, so mechanical design must keep the target inside that band with margin at both ends.
Repeatability is 5–10% of the sensing distance, giving a practical resolution of a few tenths of a millimetre. That is entirely adequate for gap checking and wear trending. If you need micron-level measurement, an inductive analog sensor is the wrong technology and you should be looking at a dedicated displacement sensor.
Which should you order?
Choose 0–10 V for short runs inside a single machine or panel where the electrical environment is quiet. Choose 4–20 mA when the cable run is long, when drives and large motors are nearby, or when you need to detect a broken cable.
Related reading
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