Sniffing a proprietary data line at 47.5V
Two options. 

Option 1. If data is fully swinging from 0V to 47.5V then a voltage divider using two resistors is fine. Choose values of resistors that are not too low so that excessive power is dissipated. Check also to see how much the line can be loaded with. If necessary, make a pseudo scope input from 1Mohm and 100k potential divider - this will produce about 4.3Vp-p BUT, you may need to put 22pF across the 1M and 220pF across the 100k to keep "edge" information in the data stream clean.

Option 2. If the data is 5Vp-p superimposed on a dc level of 47.5V then it's more complex - this is like "phantom power data" and to "read" the 5Vp-p data you need to remove the DC by using a capacitor - this leaves you with an AC data signal that is 5Vp-p but undulating up and down with the average mark-space ratio of the signal. 

If the data is encoded in such a way that there are always data edge transitions then that's fairly easy - connect the dc-removed signal into a signal comparator that has a 0V/5V output  then feed that into your analyser. However, if the data is similar to UART data, there will be long periods when the signal is 1 or 0 and this is a problem that you may never solve easily.