This is the filter design I used in my project and works very well, Mine worked on a 24V system.
Depending on what push buttons/limit switches you have, R2,R4&R5 place a small load on the push buttons or limit switches as the data sheet for mine recommended they had to have a small amount of current flowing through them to give a positive switching action(I tested this on of the machines that used the same type limit switch and they had 47 milli-amps flowing through them). D2 can be any Schttky didoe, D1can be a Transil-doide or zener diode. C1,C2 & C3 act as a filter and R1 helps limit the current, R2 just makes sure the pin is held high, When the push button is pressed the output goes low.
In my project I have 3 push buttons and 4 limit switches and each one as the input filter added.
Like I mentioned my system was 24V so I've changed the values of R3,R4 & R5 which draws about 30mA and I've only simulated this, You may just want to build and try it on a 48V system to test first and make sure you only get 5V to the input pins
