Inductive and capacitive proximity sensors look nearly identical and mount the same way, but they detect by completely different physics — and that difference decides which one will work in your application.
Side by side
| Inductive | Capacitive | |
|---|---|---|
| Detects | Metals only | Metals, plastic, glass, liquid, grain, wood |
| Principle | Eddy currents in a magnetic field | Capacitance change in an electrostatic field |
| Typical range | 1–50 mm by size | 8–15 mm |
| Affected by dust and oil? | Rarely | Yes — build-up shifts the trigger point |
| Affected by humidity? | No | Sometimes, at high sensitivity |
| Needs setting up? | No | Yes — sensitivity must be adjusted |
| Senses through a wall? | No | Yes, through non-metallic walls |
| Relative cost | Lower | Higher |
| Robustness in dirty plant | Excellent | Moderate |
The decision rule
If your target is metal, use an inductive sensor. It is cheaper, needs no adjustment, tolerates contamination far better, and reaches further for the same barrel size. Only choose capacitive when inductive genuinely cannot do the job.
When capacitive is the right answer
- The target is not metal — plastic bottles, glass jars, cardboard cartons, wooden pallets.
- You need to sense through a wall — level detection through a plastic or glass tank, with nothing penetrating the vessel.
- You are detecting bulk material — grain, sugar, flour, cement or plastic pellets in a hopper or silo.
- You need to detect liquid in a pipe or vessel without a wetted probe.
When inductive wins decisively
- Dirty environments — a non-metallic film of oil, coolant or dust barely affects an inductive field, but changes what a capacitive sensor sees.
- High humidity or wash-down — moisture on a capacitive face causes false triggering.
- Longer range needed — an M30 inductive sensor reaches 15 mm and an M80 reaches 50 mm, well beyond typical capacitive range.
- Fit and forget — no sensitivity to set, and nothing to drift.
The trap: capacitive drift
The most common capacitive complaint is a sensor that worked perfectly at commissioning and began false-triggering weeks later. The sensor has not failed. What has changed is its environment — product build-up on the face, higher ambient humidity, or a moisture film after wash-down.
The fix is to set sensitivity with realistic conditions in place, not on a clean bench: allow for build-up, leave margin, and re-check after the plant has run for some time. Where build-up is unavoidable, mount the sensor so material sheds off the face rather than collecting on it.
What about photoelectric?
If neither suits — the target is non-metallic and the range you need exceeds 15 mm — the answer is usually a photoelectric sensor. Through-beam reaches many metres and detects anything opaque regardless of material, at the cost of needing units on both sides of the gap.
Quick reference
| Your target | Use this |
|---|---|
| Steel or aluminium part | Inductive |
| Plastic bottle on a conveyor | Capacitive or photoelectric |
| Liquid level through a plastic tank | Capacitive |
| Cardboard carton across a wide conveyor | Photoelectric (through beam) |
| Grain level in a silo | Capacitive |
| Metal part in heavy coolant | Inductive |
| Label on a backing web | Fork photoelectric sensor |
Related reading
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