Ind Prox
Drives an LC tank at 100–500 kHz inside a ferrite-cup-core coil, monitors the tank's amplitude, and switches a solid-state PNP/NPN output when a metal target enters the field and damps oscillation below a preset threshold.
An LC oscillator with the coil as the inductor runs at its natural resonance. When a metallic target enters the field, eddy currents inside the target dissipate energy, lowering the tank's Q and amplitude. A peak detector and Schmitt comparator with hysteresis convert the amplitude drop into a clean digital output. Different target metals (steel vs aluminium) give different sensing distances; 'factor-1' sensors compensate for this with frequency tuning.
In plain terms
Like a tuning fork that rings until you damp it with a finger — the LC oscillator hums on its own, but a metal target steals energy and the hum dies.
Why designers use it
- Sealed solid-state replacement for mechanical limit switches — no contacts to wear in dirty, oily, vibrating factories.
- M8 to M30 standard housings — drop-in replacements across machine builders globally.
- 10⁹+ cycle life — beats reed switches and microswitches by decades.
- Fast — 5 kHz switching frequency catches passing teeth on a steel gear at 30,000 RPM.
Best for
- Limit switches
- Tooth count
- End-of-travel
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- For non-metallic targets — plastic, wood, fluids are invisible; pull capacitive or photoelectric.
- Where space and weight are tight (medical, robotics finger sensing) — small-format MEMS switches or magnetic encoders fit better.
Common mistakes
- Mounting two flush-type sensors face-to-face within their mutual range — they couple and deactivate each other; spec the minimum side-by-side spacing in the data sheet.
- Skipping the metal-target derating factor on aluminium — the actual sensing distance is 30–40 % of the steel-rated value, and a part trips intermittently when 'within range' on aluminium.
Where you will find it
- An IFM IM5135 inductive proximity sensor on an injection-moulding machine watches the mould-clamp position: at the end of clamp-close travel, the steel platen comes within 2 mm of the M18 sensor face, the LC oscillator collapses, and the machine controller advances to injection.
- A Pepperl+Fuchs NBN30-30GM50-WS-FE tooth-counter sensor on a Bosch Rexroth gearbox reads passing teeth on a 60-tooth steel ring at 3000 RPM: the chip's 5 kHz switching frequency keeps each tooth's pulse cleanly resolved for the rotary speed counter PLC input.
- A Sick IM12 inductive sensor on a stamping press watches the slide's bottom-dead-centre position: the press's safety system relies on the chip's 1 ms response time to detect over-travel and kill the hydraulics before the slide bottoms onto the die.
A short history
An inductive proximity sensor detects a metal target without physical contact. An alternating magnetic field induces eddy currents in the target, changing the behaviour of the sensing coil. Electronics detect that change and produce an output, making this approach useful for sensing the presence of metal parts.