Choosing the Right Inductive Sensor: NPN vs PNP for 24V DC Metal Detection & Relay Control System

weld 80481 34

Treść została przetłumaczona

Zobacz oryginalną wersję tematu

Reply | New topic

#31 14262952 28 Dec 2014 10:41

mrrudzin mrrudzin

Level 39

» | Helpful post? (0)

Post #31
14262952 28 Dec 2014 10:41

It is possible, it is probably worth using protection diodes and some current limiting resistors (in case they both work at the same time).

I understand that after hovering over one axis, you want to have + on the output, and on the other -?
But what would it do next? Usually logic inputs are two-state (0,1)
ADVERTISEMENT
#32 14265337 28 Dec 2014 20:14

amnon amnon

Level 10

» | Helpful post? (0)

Post #32
14265337 28 Dec 2014 20:14

Hello,

1 sensor for homing 1 axis, so I have 3 axes and three sensors. It works in such a way that I place one sensor on the left or right side of each axis. The control program, in this case mach, after the command "home the machine" starts the cycle of sliding each axis to the place where I have sensors. First, the z axis, after the approach, the coordinate is read, then the Y axis and the X axis. The machine thus sets its machine zero. So the sensor is only supposed to turn off.

Regards
Amnon
ADVERTISEMENT
#33 14265352 28 Dec 2014 20:19

mrrudzin mrrudzin

Level 39

» | Helpful post? (0)

Post #33
14265352 28 Dec 2014 20:19

Ok, so how would you like to base your axes now using these sensors?
I understand that one homing sensor = one controller input
The problem is that one is NPN and the other is PNP? The NPN sensor can control the relay / optocoupler, and the output signal from the optocoupler should only be fed to the controller input
ADVERTISEMENT
#34 14265640 28 Dec 2014 21:13

amnon amnon

Level 10

» | Helpful post? (0)

Post #34
14265640 28 Dec 2014 21:13

Hello,

It is important that all sensors are connected once (probably in parallel) so that after hovering over any sensor, the circuit is disconnected, which will cause the program to stop temporarily, read the coordinate and continue to homing the other axes. Before that, I had limit switches connected in parallel, which worked in the same way, i.e. disconnected. The problem is whether PNP and NPN will work together.
#35 14269681 29 Dec 2014 22:03

mrrudzin mrrudzin

Level 39

» | Helpful post? (0)

Post #35
14269681 29 Dec 2014 22:03

For me, it is not entirely logical all the time.

Answering the question - if you want to know that any of the sensors has been triggered, you need to pass the NPN sensor output to the relay. Connect the NO contact of the relay under + and in parallel with the PNP sensor output.
Create an account, log in and become active in a forum and ads will not appear. You will receive points by participating in discussions.
Join this discussion.

Install the application

Reply | New topic

Report a violation of the law

Topic summary

The discussion revolves around the selection of NPN vs PNP inductive sensors for a 24V DC metal detection and relay control system. Key points include that both sensor types can function in the described application, with NPN sensors shorting to ground and PNP sensors shorting to the power supply when activated. Users emphasize the importance of matching sensor polarity to avoid faults and suggest that PNP sensors are generally preferred for ease of connection and compatibility with microcontrollers. The conversation also touches on the implications of using normally open (NO) versus normally closed (NC) configurations, redundancy in sensor setups, and the potential for using both sensor types in a single system. Additionally, there are considerations regarding the wiring of sensors to PLCs and the impact of connecting different sensor types in parallel.
Summary generated by the language model.