Sensors troubleshooting answers
4 questions with answers cited from the manufacturer manuals.
- 03-wire NPN optical sensor stopped detecting, how to test with multimeter?
When a 3-wire NPN optical sensor fails to detect, it usually points to a wiring issue, a power supply problem, or the sensor itself has failed. The NPN output switches the common (negative) side of the load. You can use …
- 0Proximity sensor LED on, but PLC input off: NPN/PNP mismatch?
When an inductive proximity sensor's LED illuminates but the PLC input remains off, it often indicates a wiring mismatch between the sensor's output type (NPN or PNP) and the PLC's input type. This prevents the PLC from …
- 0Thermocouple reading jumping or showing open-sensor value?
Erratic or open-sensor readings from a thermocouple often point to issues with the sensor's connection to the controller. These sensors generate very small voltages, making them highly susceptible to interference and con…
- 04-20 mA pressure transmitter reads below 4 mA or zero on PLC, what to check?
When a 4-20 mA pressure transmitter reads below 4 mA or zero, it indicates a problem with the signal loop, power, or the transmitter itself. This usually means the PLC isn't receiving a valid signal. Start by verifying t…