How to Change the PNP Proximity Sensor to NPN?
The proximity sensor is a general term for sensors that replace contact detection methods such as limit switches and are designed to detect without touching the detection object. It detects the movement and presence of objects and converts them into electrical signals.
The principle of PNP and NPN sensors is to use the saturation and cut-off of triodes to output two states, which belong to switch sensors, but the output signals are diametrically opposite. high level and low level. NPN output is low level 0, and PNP output is high level 1.
What should I do if the proximity sensor PNP (NPN) is wrong?
PNP proximity sensor outputs a high-level voltage. NPN proximity sensor outputs 0V / GND. We need to know the output characteristics of the ATO proximity sensor.
Method 1: Add an NPN transistor to the output.
NPN transistor output conditions:
- Uc>Ub> Ue: When "b" input voltage is 24V (high level), “out” is connected to GND/0V.
- When "b" input voltage is 0V (low level),“out” outputs 24V (high level). The conduction conditions of the NPN transistor. Take the modification of a PNIP proximity sensor as an example, Connect an NPN type transistor to the output, Collector "c" will be connected to "GND/OV" The function realized at this time is the same as that of the NPN proximity sensor.
Method 2: Connect the relay.
Connecting the relay directly is the easiest way. Use the output terminal to connect the coil +/- of the relay, Then use the relay contacts to output +V or GND/0V.
Try to do an experiment
This is a PNP-type proximity sensor.
- Connect its power cord to the switching power supply, blue connects to 0V brown connects to 24V. The black output terminal is connected to the relay coil V+, and 0V is connected to the relay coil V-. Another 0V wire is connected to the NO/NG contact of the relay.
- Connect the output terminal of the proximity sensor to the black test lead and the red test lead to the positive pole: of the power supply to measure the voltage. The measured voltage is +24V, So the relay contact outputs OV (low level).
- After triggering the proximity sensor, one of the outputs was also measured as a positive voltage. Therefore, it can be determined that the entire system is equivalent to an NPN proximity sensor at this time.
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