A capacitive proximity sensor will switch on a metal target, because metal presents a high dielectric constant that strongly perturbs the sensor's electrostatic field [S2].
An inductive sensor, by contrast, is built specifically around eddy-current loss in a metal target and is the default choice when the job is "detect metal, ignore everything else" on a production line [S1].
Detection Principle: Electric Field vs Electromagnetic Field
An inductive sensor drives a high-frequency current through a coil, generating an electromagnetic field at its face. When a metal target enters that field, eddy currents form on the target surface, the oscillator amplitude damps, and a threshold detector flips the output. The mechanism is loss-based and inherently metal-selective [S4].
A capacitive sensor treats the target and the sensor face as two plates of a capacitor and watches the resonant frequency shift as any material with a dielectric constant above roughly 1 enters the field. Metals, water, plastics, glass, wood, paper, and powders all shift the capacitance, which is the entire point of the technology, and the reason it is the standard pick for liquid level in tanks and for pellet/granulate detection in hoppers [S3][S7].
Can a Capacitive Sensor Match Inductive on Metal? Direct Answer
On a clean bench with a flat steel target, both technologies will detect the same piece, but the inductive sensor will do it at roughly 1.5–2x its nominal range while the capacitive sensor is derated heavily, often to 50–70% of nominal, because the metal target's effective area is small relative to the capacitive electrode geometry [S1][S4].
Capacitive sensors also trigger on everything around the target: condensation, coolant film, a passing operator's hand, even humidity swings of 10–20% RH, which is why they are specified with explicit compensation pots and grounded-shield variants rather than as drop-in metal detectors [S5][S8]. For a control engineer who needs to confirm a steel bracket is seated in a fixture, the inductive sensor is the only honest answer; for a level switch that must see plastic pellets through a 5 mm PP wall, only capacitive will work [S1][S4].
Selection Criteria: Range, Environment, Mounting, Output
Rated sensing range is the first gate.
Environment is the second gate. Inductive sensors carry IP67/IP69K ratings as a baseline, tolerate cutting fluid, weld spatter, and oil mist, and are unaffected by non-metallic contamination on the target face [S1][S5]. Capacitive sensors share the same housing ratings but the field extends through the housing wall, so conductive films (coolant, hand sweat) and changes in ambient humidity can shift the trip point; many vendors require a separate guard or grounded shield for washdown zones [S5][S8].
Output and wiring close the decision. Both families ship as PNP (sourcing) or NPN (sinking), 3-wire or 4-wire, 10–30 VDC, with NO, NC, or complementary outputs; the IFM203 inductive family is a typical example of dual PNP/NPN in a single housing, and capacitive bodies reuse the same pinouts, so a panel builder does not have to rewire when swapping technologies [S1][S4].
Side-by-Side Comparison on Four Decision Criteria
Material scope: inductive covers ferrous and non-ferrous metals only; capacitive covers metals plus plastics, glass, wood, liquids, paper, powders, and granular media [S1][S2][S4]. Environmental immunity to oil, coolant, dust, and humidity: inductive rated as a baseline, capacitive requires shielded electrodes, ground straps, or compensation [S5][S8]. False-trigger risk in a mixed-material line: inductive near zero when the target is the only metal present, capacitive elevated and a function of the surrounding dielectric stack-up [S4][S6].
Where Capacitive Sensors Outperform, and Where They Fall Short
Capacitive sensors are the correct tool for non-contact liquid level through a glass or plastic tank wall (typical dielectric of water is around 80), for tablet/capsule counting on a packaging line, for paper-stack height detection where the inductive sensor simply does not respond, and for detecting the presence of plastic pellets inside a hopper through a non-metallic sight glass [S1][S4][S7].
Capacitive sensors quietly fail in three patterns. First, an ungrounded operator reaching into the field shifts capacitance and causes a phantom trigger; the fix is a grounded shield around the active electrode. Third, build-up of conductive residue on the electrode face shifts the trip point over a shift and forces a clean-and-recalibrate cycle that an inductive sensor in the same position would not need [S4][S5].
Standards, Sourcing, and Field-Proven Use Cases
Most industrial proximity sensors on the EU market carry an ATEX/IECEx marking for Zone 1/21 when the datasheet states it, and the inductive family is the dominant choice for hazardous-area metal-presence detection because the sensing field is contained and the housing is fully potted [S1]. PNP output remains the dominant wiring convention in European panels, with NPN still common in Asian-built machinery; matching the sensor's output type to the PLC input card is a routine check that prevents a no-fault-found commissioning delay [S1][S4].
For a fair bench test, place a 1 mm thick mild-steel target at half the inductive sensor's nominal range and at the capacitive sensor's full nominal range, then sweep humidity from 30% to 80% RH: the inductive trip point will move under 5%, the capacitive trip point commonly drifts 15–25% on unshielded bodies, which is the empirical gap the spec sheet does not show [S5][S8]. For engineers who must compare sensor families across more than just proximity, the same disciplined framing shows up in adjacent decisions such as the Smoke Detector vs Combustible Gas Detector: What Each Sensor Actually Sees trade-off, where the wrong "metal-only" mindset causes the same kind of mis-specification.
Component reference pages worth checking: metal material.