Sensors

Sensors convert a physical quantity — distance, temperature, pressure, position — into an electrical signal the controller can read. Sensor choice usually determines accuracy, response time, and cost more than the controller itself.

Overview

Specify sensors by measurement range, accuracy, repeatability, response time, output type, supply voltage, environment (IP/NEMA rating, temperature, vibration), and certification (UL, ATEX, IECEx) where required.

Proximity & Presence

Inductive — detects ferrous (and non-ferrous) metals, ~0–60 mm.
Capacitive — detects metals, liquids, plastics; through-wall sensing.
Photoelectric — through-beam, retro-reflective, diffuse.
Ultrasonic — distance to liquids, transparent or dark objects.
Laser distance — sub-mm precision; time-of-flight or triangulation.
Vision — pattern matching, OCR, dimensional gauging.

Temperature

Thermocouple — wide range, fast, low cost (J, K, T, E, N, R, S, B).
RTD — Pt100 / Pt1000; very stable; −200 to 850 °C.
Thermistor — NTC/PTC; sensitive, narrow range.
IR pyrometer — non-contact, moving / hot surfaces.
Semiconductor (LM35, TMP117, DS18B20) — easy digital interfacing.

Pressure, Flow, Level

Pressure — piezoresistive, capacitive, strain-gauge; gauge, absolute, differential.
Flow — Coriolis (mass), magnetic (conductive liquids), vortex, turbine, orifice, ultrasonic, thermal mass.
Level — radar, ultrasonic, hydrostatic, capacitive, guided-wave, float, optical.

Position & Motion

Encoders — incremental (A/B/Z) and absolute (SSI, BiSS, EnDat).
Resolvers — rugged angular position.
LVDT — linear displacement, very robust.
IMU — MEMS accelerometer + gyro + magnetometer.
Load cells / strain gauges — force and weight.

Signal Types

Digital (24 VDC) — PNP (sourcing) or NPN (sinking).
4–20 mA — current loop; immune to voltage drop.
0–10 V — common analog input.
HART — digital overlay on 4–20 mA.
IO-Link — smart sensors with config + diagnostics over standard cable.
Fieldbus / Ethernet — PROFINET, EtherNet/IP, Modbus, EtherCAT.