In this guide
A sensor is cheap compared with the line it stops, but ordering the wrong one still costs time. Start with what it has to detect, then check the details that make a replacement physically and electrically compatible.
Pick the technology from the target
| Technology | Detects | Watch out for |
|---|---|---|
| Inductive | Metal objects | Range is rated on mild steel. Stainless steel, brass, aluminium and copper reduce it |
| Capacitive | Almost any material, including liquids, powders and plastics | Sensitive to dirt build-up and humidity. Often has an adjustable sensitivity |
| Photoelectric | Objects of most materials by light | Dust, lens fouling, shiny or transparent targets and ambient light |
Photoelectric types
- Through-beam: separate emitter and receiver. Longest range and most reliable
- Retro-reflective: one unit and a reflector. Needs the reflector to stay clean and aligned
- Diffuse: one unit that sees light bouncing off the target. Easiest to install, most affected by target colour and background
Details that decide whether a replacement fits
- Sensing distance: the rated range, and the mounting distance you actually use
- Mounting style: thread size such as M8, M12, M18 or M30, or a rectangular body
- Flush or non-flush (inductive): flush sensors can be mounted level with metal. Non-flush sensors reach further but need free space around the head
- Output: normally open or normally closed, and the output type
- Connector or cable: M12 or M8 plug, or fixed cable of a given length
- Supply and enclosure: supply voltage, temperature range and IP rating
PNP and NPN
A PNP output switches the positive supply to the input. An NPN output switches the load to zero volts. The PLC input must suit the sensor: a PNP sensor needs a sinking input and an NPN sensor needs a sourcing input. Check the input module's manual rather than assuming, and note that NPN is more common on equipment from some regions.
What to send us
- The full model number printed on the sensor body, or a clear photo of it
- The machine it came from and what it detects
- The thread size, sensing distance, output type and connector if you can read them
If the label is worn away, send what you can see along with the application. We will tell you what we can match and what needs checking.