Comparator: What is appropriate for comparing ranges of about 50-100 mVs? Can I use an LM741 op amp?
The allowable input voltage range for a 741 is 2 volts inside the power rails. This means that on a +/-15V supply, the inputs will still adequately function from -13V to +13V.

If you are trying to tempt performance from a 741 with a grounded negative rail then don't expect the inputs to function lower than 2V above ground and worst case 3V.



Let's look at a few other things too.


Input offset voltage maximum of 6 mV
Input offset voltage drift with temperature 15 uV / degC
Input resistance - maybe as low as 300kohm
Input offset current up to 500 nA
Output voltage swing (from a +/-20V supply) limited to +/-16V


My advice is this - don't use it - pick a better device - even the LM324's inputs encompass the neg rail. My general purpose work-horse op-amp is the AD8605 because it's not at all like the 741 and comes in single, dual and quad packages.