Three-wire sensor how to use a multimeter to measure the good and bad
Commonly used three-wire system of the sensor, tube it is NPN type or PNP type, direct measurement with a multimeter.
The sensor, 24V power supply, multimeter three constitute a circuit, multimeter to DC gear. Blue line connected to the power supply negative, brown line connected to the power supply positive, black line connected to the multimeter black pen or red pen, the rest of a pen lap connected to the power supply positive terminal or negative terminal.
At this time, when the NPN or PNP sensor work, the multimeter to measure the voltage is the power supply voltage, should be 24VDC, when the multimeter left a pen to lap the power supply positive terminal, at the same time there is an object close to the sensor, the multimeter has a 24V voltage display, indicating that the sensor is a NPN-type sensors and normally open type, no object close to the multimeter has a 24V voltage display, indicating that it is a NPN-type sensors and normally closed type. When there is no object close to the sensor, the multimeter will show 24V, which means the sensor is NPN type sensor and normally open type.
If the multimeter is left with a pen on the negative terminal of the power supply, at the same time there are objects close to the sensor, the multimeter has a 24V voltage display, indicating that the sensor is a PNP-type sensors and normally open type, no objects close to the sensor and the multimeter has a 24V voltage display, indicating that the PNP-type sensors and is normally closed type.
So, for this topic if the sensor can not see the logo, it is only through the measurement to judge the more reliable. But remember, NPN-type sensor is also known as the proximity switch, its output is a low-level signal, to put it bluntly is the negative pole of the 24V power supply, PNP-type sensor its output is a high-level signal, that is, the positive pole of the 24V power supply.
