Proximity and photoelectric sensors detect parts, position and presence on a machine. They look simple, but a replacement has to match several electrical and mechanical details to work with your control system. Here's how to spec one.
First, the sensing type
- Inductive proximity: detects metal only, short range, very robust.
- Capacitive proximity: detects almost anything (liquids, plastics, powders).
- Photoelectric: detects objects by light — modes are through-beam (longest range), retroreflective (uses a reflector), and diffuse (reflects off the target).
Mechanical fit (proximity sensors)
- Body size/thread: M8, M12, M18, M30 (or rectangular).
- Shielded (flush-mountable in metal) vs unshielded (longer range, must be non-flush).
- Sensing distance (Sn) — must reach your target.
Electrical match (this must match your PLC)
- Output: PNP (sourcing) or NPN (sinking) — must match the PLC input card.
- Output state: normally open (NO) or normally closed (NC).
- Wiring: 2-wire, 3-wire or 4-wire; voltage usually 10–30V DC.
- Connection: pigtail cable or M12 connector (and pin count).
Why the wrong sensor 'fits but doesn't work'
A sensor can thread in perfectly and still fail to trigger the PLC if the output is NPN where the input expects PNP, or NC where the logic expects NO. Always match the output type and wiring, not just the size.
Send us the old sensor
Give us the part number (or a photo and the body size), and tell us what it detects and how it wires to your PLC. We'll cross-reference a verified equivalent from the major sensor brands and quote it.