need isolated voltage conversion

first to clear the scenario , i want to data log a 0-15v signal from a system(a thyristor firing card) via arduino ADC port (0-5v) ,without disturbing the system .to sum up what can i use to keep the system isolated yet get a linear attenuated signal for arduino adc.

1)opamp for attenuation ?
2)attenuation by resistor network + opamp buffer ?

Your question, seems to me too abstract.

  1. How you evaluate "not disturb" ? Current consumption / voltage drop / interference by measuring circuitry? What is current, frequencies, waveform / modulation?
  2. Isolation, you mean galvanic isolation?

You could feed the 0-15 volts via a fixed loading resistor after it's fed the thyristor or whatever and monitor the current flowing via a hall effect sensor. The sensor will give an analogue output proportional to the input current - which is proportional to the drive voltage.

@Magician ,yes i mean galvanic isolation . when i'll take voltage across any resistance on the card it will drain some current thus may disturb the equipment .. i dont want to take such risks cause the cards are way to expensive to experiment on :drooling_face: ..

If you persist in not saying what you are doing we can’t supply an answer. What you have posted so far makes no sense.
Applying galvanic isolation is also going to drain power from this card, what ever it is.

@Grumpy_Mike i am making a testing equipment to log the voltage values at some intervals and make a trend graph.. thats all im doing, as i have told before :roll_eyes: .. e.g linear optocoupler might work aswell..i just want to confirm what are the norms when we want a linear voltage with minimal loading effect as in multimters ..

To get a minimum load effect you use something with a high impedance. If you use an opto isolator that has much more of a load effect on the circuit because you are having to light an LED which takes about 5 to 15 mA. This corresponds to a load of 1K for a 5V system. This is hundreds of times more load than a high impedance input.

Hmm ,, good point :roll_eyes: ... this means , an op-amp buffer and attenuation by factor of 3 by op-amp would be a good option it would have a high input impedance and do the job .. thnx bro