This is how you can test proximity switches directly with a multimeter
Firstly, there are three-wire ones, and three-wire proximity switches are used more often. The output is divided into NPN and PNP two kinds. Three-wire proximity switch is the need for additional power supply to work, so before measurement to give him power, the general wiring is brown to 12-24VDC, blue to 0V, black is the signal output. We connect the wires and power on, take something to the front of the proximity switch, try to lean closer, if the proximity switch detects the object, his output indicator will be bright. This is a prerequisite is that you want to know what the proximity switch is detecting, if you do not know you can try a few more objects, such as metal, magnets and so on. If these have tried, the indicator light did not light, then you can use a multimeter to measure. Do not need to care what type of proximity switch, as long as the measurement of the signal line and 24V or 0V voltage can be, see if there is no voltage. If there is no voltage, it means that this proximity switch is bad. If the indicator light is on, then it is good, no need to measure.
Next is the two-wire, two-wire proximity switch does not need additional power supply, but also divided into two kinds of connection. The measurement method is basically the same as the three-wire one. The colours of the two wires are generally brown and blue. The first connection is that the blue wire connects to 0V and the brown wire connects to the signal. Still use an object close to the proximity switch, if the proximity switch is good, the indicator light will be on, if not, you can use a multimeter to measure. Measure whether there is any voltage between the signal wire and 24V. No is bad. The other connection as well as the measurement is just the opposite.
