Cap Prox
Generates a 100 kHz–1 MHz electric field at its sensing face; when a target enters the field, dielectric loading raises the oscillator's loaded capacitance, the demodulator detects the amplitude/frequency shift, and the chip flips a PNP/NPN transistor output.
An LC oscillator with the sensing electrode as one plate runs at a tuned frequency. A target's permittivity loads the capacitor, increasing C and lowering oscillation amplitude (or frequency). A peak detector and Schmitt comparator convert the shift into a digital ON/OFF with hysteresis, and a current-output stage (4–20 mA in IO-Link variants) reports analog distance.
In plain terms
Like an old-school theremin — the player's hand near the antenna shifts the oscillator's frequency, and the proximity switch listens for that same dielectric-induced shift.
Why designers use it
- Detects non-metallic targets — plastic bottles, wood pallets, paper bags, water columns, all invisible to inductive sensors.
- Through-thin-wall sensing — a proximity sensor mounted outside a 3 mm acrylic tank reliably detects fluid level inside.
- Sealed in M12/M18 stainless housings with IP67/IP69K — survives factory wash-down and oily environments.
- Programmable sensitivity — the user dials in the trigger threshold to ignore the empty container and respond only when product enters.
Best for
- Bin-full sense
- Bottle detect
- Through-wall level
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
- Where humidity or condensation films the sensor face — the dielectric of water creates false detections.
- Around metal-rich environments where the metallic chassis is closer than the target — the chassis swamps the field.
Common mistakes
- Mounting two capacitive sensors face-to-face within their sensing distance — they couple to each other and oscillate together as one big antenna, both showing 'detect'.
- Skipping the EMC ferrite on the cable — long unshielded leads pick up VFD noise and the comparator chatters.
Where you will find it
- A Sick KT5W capacitive proximity switch on a Krones bottle-filling line in a Spanish brewery detects the presence of a glass bottle through a 4 mm phenolic guide — the dielectric shift from the empty bottle alone triggers the filler valve at 60,000 bottles per hour without any mechanical interlock.
- A Turck BCC5-S capacitive sensor on a grain elevator at an ADM mill in Iowa monitors a steel auger trough through its plastic side window: when the wheat level reaches the sensor, the bin-full output stops the upstream conveyor before grain backs up into the elevator.
- A Pepperl+Fuchs CBN15-30GS capacitive proximity sensor on a Tropicana orange-juice carton-erecting machine detects the presence of a folded carton blank through the magazine wall: the chip's PNP output triggers the suction cup grab at 100 cartons/minute even after operators replace flute thickness mid-run.
A short history
A capacitive proximity sensor detects objects by measuring changes in capacitance. Its electrode generates an electrostatic field; when a target approaches, it alters this field, so capacitance increases as the object nears. An oscillator's frequency or amplitude shifts accordingly, and electronics convert this into a switching output. Unlike inductive sensors, capacitive types can also detect non-metal materials like liquids and plastics.