Using npn Inductive sensor for end stop.

Hi can someone tell me if mine are broken.
i cant understand these. They are stock part on the cnc machine.
And would like to keep it stock. 

here is one of the switches. Attached.

I use an new 7i76U board. And can easy just trigger the end stop pin with a wire from positive source (+)

Since this gives reverse. I did think to add a relay.
but the relay just stays on.

How do these work. I get constant 24 volt.
but when messure resistanse it does from 4ohm to 40ohm.
so something is happening. When it switches and led goes on/off too.

Anyone know these.
https://photos.app.goo.gl/jcqMZvWbBJQ8ZE1p6https://photos.app.goo.gl/jcqMZvWbBJQ8ZE1p6

To use NPN sensors with 7I76U inputs (which need a positive signal to actuate),
you must add a pullup resistor to each 7I76U input connected to a NPN switch.

+24V --> resistor_pin_1 --> resistor_pin_2 --> NPN output + 7I76U input

Suggested resistor value is 2.2K 1/2W

(PNP sensors need no additional components)

I think this is where my confusion comes in.

Because i only have one pin to use.
The home input.

I hooked up an external power supply.
And a switch from the positive lead.

Would this be the correct ting to do. Attachement 1.
Or do I need to add an extra resistor prior to the pin in or prior to npn signal.


Feeling like swimming with no land in site.

So im must be going about this the wrong way.
My brain hurts trying to think about this.
Im honestly trying.

Maybe best to get some other switches.

Hi, i also use NPN Sensors for homing and limit switches by my 7i96s without any resistors.
I thing it is also by the 7i76u not nessesary to use a resitor. The i/o's should work from 5 to 28V. Description Screenshot from mesa below.

It is not very difficult to bind the sensors:  L1 (brown) to DC 24V current power ,  L- Blue on ground.  The switch cable ist  Black (BK) an is to connect to the input pin of 7i76u.

But, please without guarantee.


 

Rune_cnc:

Yes, your picture with the NPN sensor and 2.2K pullup to +24V is correct.

hermann1976:

The 7I96/7I96S can work without resistors with PNP or NPN sensors.
This is because they have a floating common pin for their inputs so can
sense either a connection to positive (PNP)  or negative (NPN) voltage
relative to  this floating common pin.

The 7I76/7I76U does not have a floating input common pin so can only
sense positive voltages. Since NPN sensors do not output a positive
voltage, but just a sense dependent connection to ground, an external
resistor must be  added to pull the NPN sensor output to a positive level.

 

Thanks I got 1 of 3 to work.
So now I know i need new ones.

So I will just order som pnp
And do without extra components.
Make it easy on the "next guy" comming to repair.