what you want to do actually?
do u want to sense analog DC voltage? like 0-24V?
if its so then its very simple.
u can use voltage divider and ADC.
select any ADC that has input analog input range of 0-10 V or 0 – 12 V
using voltage divider convert your 24 V in to analog input range of ADC
thats all
now you will get digital equivlent output of your 0 – 24 V input