I have a similar issue. I want to wire 2 inductive prox. switches per axis. They can both serve as homing switches and limit switches. You will be telling the axis' which direction to home in so as long as they hit a sensor at the end of their travel, they will let the machine home. They can also double as limit switches too. I haven't decided if I will wire each set of 2 switches in parallel and connect each set of 2 to a single input on the Masso (X, Y and Z) or wire each switch to its own input on the Masso (6 inputs total) and assign them in software. I don't see anyadvantage to the latter. As far as NPN vs PNP, you can invert the normally Low/High signal state in the software so you should be able to use either sensor type with the Masso.
I'm using these: PS-05N inductive proximity switches. They've worked very well for my first machine. Just mount the sensor where it will butt against metal parts on each axis, no need to add any optical disrupt as with optical sensors.
Masso admin, please chime in here if you can comment on which method of connection might be better.
The problem with a lot of the NPN proximity switches is they don't have built in pull up resistors in them. They output nothing when idle and nothing when triggered.
In the case of the NPN switches I have when they are not active they output Power supply voltage, in my case 12 volts, and when they are triggered they drop to almost 0 volts. I'm lucky enough to have built in pull up resistors in my switches.
If you don't have the built in pull up resistor in your NPN sensor you can add a 5.6K resistor from the positive of the sensor to the output and it should work as you want. You will need to invert the input in Masso as the normal state will be high changing to low when the switch is triggered. See the diagram below.
The Masso inputs are opto isolators so they require a voltage of about 4 volts or more to see an input.
You can apply 24 volts to the inputs but I suggest you use resistors in series to limit current. Not for the sake of the input but if you have 24 volt signal wires running around your system and you short one to ground you will short out the PSU but if you have a 5.6K resistor in series with the 24 volts it will still work and grounding it in error it will cause no problem.
Looks like your post was hijacked by a rogue proxy sensor gang. Did you figure out how to solve your limit switch issue on your own?
If not then here is some information to get you started. Take a look at the Homing Inputs topic in the documentation for details on how to hook up the homing switches (hard limit switch). Once you setup the homing switches you can set the soft limits in the setup page by entering the minimum and maximum travels for each axis. Masso explains how to enter the soft limits in the axis calibration section. You can add more limit switches at the other end of travel for each axis if you wire them in parallel but that is not really necessary. Hope this helps!