multimeterprecisionvoltage measurement
I am working with a Fluke 8508A, an 8.5-digit table-top multimeter. To my surprise, one of the menu options is a 4-wire DC voltage measurement.
I know how 4-wire resistance measurements work, but I am at a loss how a 4-wire voltage measurement would be beneficial. Does it give higher precision, and if so, how?
The display is not the limiting factor (as you point out). Fundamentally, there is a cut-off. If the display was the most expensive part in the meter, then most meters would probably read up to 9999 on all digits. However, there's a couple factors that make the meter ranges what they are.
There is a limit to how high a range goes - the count is a design decision for the meter maker. A 20... meter isn't the only type available either, I personally have a 6000 count meter.
Logarithmically, you get the most bang for your buck by having 2000 counts. See the image of the number line below. By doubling the counts from 1000 to 2000, you get a bigger bang for your buck, and you also get to use one more digit (better for marketing).
There's another reason for not dropping the least significant digit. Part of the gotcha with auto-ranging meters is that you can easily forget that the meter has different measurement ranges, and that the measurement accuracy changes with each range. For example, compare the following displays:
193.00 k
.1930 M
193.0 k <----- Would you notice the missing digit as easily?
Personally, I see it as a more obvious way of conveying information about the measurement. It doesn't detract much from the readability in my opinion.
Converting a analog signal to a digital number is, oddly enough, done by something called a analog to digital converter, or often A/D for short.
There are many ways this conversion can be accomplished, like successive approximation, sigma-delta, tracking, flash, and probably a few more basic strategies. There are lots of variations and tradeoffs within the basic types too. Most microcontrollers have successive approximation A/Ds built in.
Best Answer
From page 3-5 (thanks) "4wV Allows operation with calibrators which provide a remote 4 wire sensing capability by providing connections between INPUT HI and SENSE HI and between INPUT LO and SENSE LO. The 4wV annunciator in the left-hand display indicates that 4-wire sensing is active."
I'm going to guess it's similar as remote sensing on a DC power supply. When you want to exclude the voltage drop along the wires. So very similar to 4-wire resistance.