When using a multimeter, what readings confirm the proper function of a proximity sensor?

Confirming the proper function of a proximity sensor using a multimeter depends on the sensor type and its wiring configuration. A proximity sensor detects the presence of an object without physical contact. Common types include inductive, capacitive, and photoelectric sensors. Inductive sensors detect metallic objects, capacitive sensors detect both metallic and non-metallic objects, and photoelectric sensors use a beam of light. The multimeter readings will vary based on whether the sensor is a two-wire, three-wire, or four-wire type. For a two-wire sensor, the multimeter, set to measure voltage, should show a voltage drop when an object is within the sensor's range. The voltage drop indicates the sensor is conducting and allowing current to flow. For a three-wire sensor (typically PNP or NPN), the multimeter, set to measure DC voltage, should show a change in voltage on the output wire when an object is detected. In a PNP sensor, the output voltage will switch from near 0V to near the supply voltage when the object is present. In an NPN sensor, the output voltage will switch from near the supply voltage to near 0V when the object is present. The multimeter can also be used to verify the supply voltage is within the sensor's specified range. For a four-wire sensor, the multimeter can be used to check both the supply voltage and the state of the normally open (NO) and normally closed (NC) outputs. When the sensor is not activated, the NO output should show no voltage, and the NC output should show voltage. When the sensor is activated, the NO output should show voltage, and the NC output should show no voltage. Precise voltage levels depend on the sensor's specifications, but the key is a clear and consistent change in voltage state when the target object is within the sensing range. If there is no change or an erratic change, the sensor is likely faulty.