How to directly detect proximity switches with a multimeter
The first is three-wire, and three-wire proximity switches are widely used. The output is divided into NPN and PNP. The three-wire proximity switch requires an additional power supply to work, so it must be powered on before measurement. Generally, the brown wire is connected to 12-24VDC, the blue wire is connected to 0V, and the black wire is the signal output. We connect the wires and power on, put something in front of the proximity switch, and try to get as close as possible. If the proximity switch detects an object, its output indicator light will light up. The premise is that you need to know what the proximity switch detects. If you don't know, you can try a few more objects, such as metal, magnets, etc. If you have tried these and the indicator light does not come on, you can use a multimeter to measure it. It doesn't matter what type of proximity switch it is, just measure the voltage of the signal line and 24V or 0V to see if there is any voltage. If there is no voltage, the proximity switch is bad. If the indicator light is on, it is good and there is no need to measure.
The second is the two-wire one. The two-wire proximity switch does not require additional power supply, but it is also divided into two connection methods. The measurement method is basically the same as the three-wire one. The colors of the two wires are usually brown and blue. The first connection method is to connect the blue wire to 0V and the brown wire to the signal. Or bring an object close to the proximity switch. If the proximity switch is good, the indicator light will light up. If not, you can use a multimeter to measure it. Measure whether there is voltage between the signal line and the 24V voltage. If not, it's bad. The other way to connect and measure is just the opposite.
