Voting records are not an accurate gauge of whether a senator is conservative or liberal. Bills that would appear to have a conservative nature, are often amendments to existing bills, which are already more conservative. You would have to select a certain set of bills involving crucial votes to determine if a Senator or Congressman is conservative or liberal and even, then you might not know because a conservative issue in Wyoming may not be a conservative issue in Louisiana.
Thus deciding what bills you are going to use as the benchmark is the first step you have t take. Looking at total voting records, will often give a false impression.
It has to be decided which issues are conservative and which are liberal. Depending on personal perspective, different people would label bills differently.
If you want a raw vote, check all the bills, riders, amendments, conference reports and resolution, decide which party introduced them and then run your tally. If the Democrats prevail, then all Democratic lawmakers would be viewed as liberal by some and all Republicans would be viewed as conservative. However, that would be the poorest barometer you could use.