“No output” and “random false trips” are the two most common sensor complaints on any production line. Swapping the unit rarely fixes the underlying cause — the same failure reappears on the next measuring point. Here is a probability-ordered routine that works for proximity, photoelectric, temperature, pressure and vibration types alike.
A six-step routine
Step 1 — Measure the supply. Take the reading at the sensor terminals, not at the cabinet. Inductive and photoelectric switches typically need 12–30 V DC; transmitters such as the WIKA A-10 or Beck 981 usually run on 24 V DC or a two-wire current loop. Terminal oxidation and loose ferrules cause enough voltage drop to starve a sensor.
Step 2 — Check the wiring type. Two-wire devices power themselves through the signal loop; three- and four-wire devices need separate supply terminals. Wiring a three-wire unit into a two-wire loop never works. PNP and NPN outputs are not interchangeable either — the controller input (sourcing/sinking) must match.
Step 3 — Test the output and load. With a meter from output to 0 V, a switching output should flip state when actuated. For 4–20 mA or 0–10 V outputs, disconnect the controller and measure directly — many “failed sensors” turn out to be a blown PLC analogue channel.
Step 4 — Inspect the sensing face. Metal dust on an inductive face causes constant switching; dusty lenses and reflectors are the number-one cause of false trips on photoelectric units. On high-temperature points — where sensors such as Proxitron’s 230 °C inductive range live — also check the cable jacket for heat ageing.
Step 5 — Verify range and mounting. Pressure transmitters run permanently near their range limit drift faster; thermowell insertion depth that is too shallow reads low; a loose accelerometer base (e.g. a Wilcoxon 786A) injects false vibration. A drifting transmitter needs calibration, not a zero tweak.
Step 6 — Hunt down interference. VFDs, contactors and power cables are the usual culprits. Route signal cable separately, ground the shield correctly, and for bus transmitters such as the Beck 985-Modbus check termination and bus grounding.
Type-specific notes
- Inductive proximity (Balluff BES 516 series): confirm flush/non-flush mounting and rated distance — target material affects the real switching distance.
- Temperature: WIKA TR10 Pt100 accuracy depends on two-, three- or four-wire connection; unbalanced three-wire leads are a classic fault.
- Pressure: after a Beck 901 mechanical switch trips, confirm whether it needs manual reset; on the Beck 930 Climair differential switch, check the impulse lines for blockage first.
- Humidity: a contaminated E+E EE160 / EE650 probe can be cleaned per the manufacturer’s procedure — never scratch the capacitive element.
- Flow: a jammed Höntzsch vane-wheel meter freezes its reading; scale on a thermal probe slows the response.
Replacement and spares
If the sensor does need replacing, send us the nameplate photo and mounting dimensions — current or obsolete. We match an equivalent by output type, range, voltage and process connection; common types are partly stocked and we typically return price and lead time within one business day.
- Browse the WIKA pressure and temperature range and Balluff proximity switches we carry.
- Or go straight to the inquiry form.