NPN vs PNP for homing

Hi all,

I am willing to use proximity sensors for my lathe rebuild.
These will be the homing sensors.

I am curious why PNP is recommended more over NPN. I have a wiring diagram that says if use NPN i have to ad a pullup resistor.
But PNP is recommended.

Could some one explain me why?


Erik

it depends on the input type

For sourcing type inputs ( that have a built in pullup resistor to + control power ),
NPN switches are appropriate.

For sinking type inputs ( that require a connection to + control power to be activated ),
PNP switches are appropriate.

For example, with optocoupler inputs the wiring would be as follows

Sourcing input current path: +control_power --> resistor --> opto_anode --> opto_cathode --> NPN_out --> gnd

Sinking input current path: +control _power -->PNP_power --> PNP_out --> resistor --> opto_anode --> opto_cathode --> gnd

You may tell us what Brel out Board you are using
LJ12A3-4-Z-BX They are very Stable to use

You can use the NO Normal Open ones
or Normal Close NC ones
NC is better as it showes always functionality if error they wont work
BUT also the NO ones fail signal as they break on the touch and your mashine will notice it
IT Runs to the oposit Home so Defekt is no BREAK

Ofcourse, I forgot to mention the board I'm using.
I'm using Mesa 7i76e.

Yeah, the 7I76/7I76E/7I77 use sinking inputs so PNP sensors are the easiest to use