Inside the new Agilent TrueVolt 34461A 6.5digit bench multimeter. A replacement for the venerable 34401A.

Photos:

http://www.flickr.com/photos/eevblog/sets/72157634225126018/May as well start the thread.

I previously read a bit about multi slope III, don't know what IV changes.

Agilent's multi slope conversion is more like a slow delta sigma conversion.

You have an integrator with two comparators and inject the unknown current and a + or - reference current so the voltage on the integrator capacitor bounces between the comparator limits. Over time the ratio of time spent injecting + and - reference currents tells you what the unknown current is. Accuracy doesn't depend significantly on anything but the accuracy of the reference current. The comparators don't have to be accurate they just keep the integrator voltage in bounds.

For more accuracy in less time you measure the voltage on the integrator capacitor at the start and end of the conversion period. The current injection ratio gives you the most significant measurement bits and measuring the initial and residual integrator voltage can give you another 8, 9, 10? bits.

The integrating capacitor doesn't have to be stable or accurate, you can easily calibrate it with the reference current. Dielectric absorption might still be an issue with this type of converter.

The manual recommends using the 10A input for currents over 1A. The 10A input has a fixed 10A full scale range.

Bits left of the board are interesting - wonder if there is another model to come or maybe they are alternate rather than additional parts, perhaps for the 60A?