There are voltmeters that can measure voltage over a wide range without the need to switch the range manually.
I'm quite curious how do they do it, because I'd like to make a tiny device capable of the same, up to 1000V. I was thinking about utilising a capacitor – if you connect it to voltage on one side, you'll get opposite voltage on other side, but high current will not flow.
simulate this circuit – Schematic created using CircuitLab
The change in potential should be measurable, shouldn't it?
If that's not the way, what is?
Best Answer
As a alternative to the common approach that clabacchio has already explained well, you can use very high resolution A/Ds that require 10s of ms per reading when the result is only to display to a human. You generally want to update a digital display in the 2-4 Hz range, so you have at least 250 ms per reading.
There are delta-sigma A/Ds available that claim over 20 bits. Let's say 8 real bits is good enough, which gives you 1/2 percent resolution. If you arrange the highest voltage of interest to maximize the output of a 20 bit A/D, then you can read a voltage 1/212 lower and still get 8 bits. For example, if you want the meter to read up to 1 kV, then it will still be able to read 1/4 volt with 1/2 percent resolution. If that's good enough, then no range switching is required. The only "auto ranging" would be in how the result is displayed to the user.