Re: high voltage measurement
Use differentilal amplifier in its basic configuration:
It allows you to divide high voltages, and in your case you want to reduce 48V to 2.5V, so the values of resistors will be 160kΩ and 8.2kΩ.
Connect 160kΩ resistor between positive pole of 48V supply and (+) of the opamp.
Connect 8.2kΩ resistor between (+) of opamp and its 0V.
Connect 160kΩ resistor between negative pole of 48V supply and (-) of the opamp, and last,
Connect 8.2kΩ resistor between (-) of opamp and its output (negative feedback).
The voltage reduction ratio will be 8.2:160 ≈ 0.052, so the voltage will be reduced from 48V to 2.5V.
To filter out noises you can connect a 100nF capacitor between (-) of the opamp and its output (in parallel with 8.2kΩ).
Regards,
IanP