microsKanner

A scanner is usually the weak link. It sits between the sensor and the bridge, and whatever uncertainty it adds lands directly on the measurement, which is why most of them are built around relays and most of them degrade the instrument they are expanding.

We wanted to keep the solid-state switching we had used in the microK, and that turned out to be harder than it sounds. The photoMOS devices have a limited off-resistance, and at the levels this instrument works at, leakage through a switch that is supposed to be open matters. The answer was a buffered switching arrangement of our own, which removes the effect of that leakage entirely.

The other decision was to stop thinking of it as a switch box. Instead of multiplexing into one front end, we duplicated the microK’s front end for every channel, so the instrument expands to ninety channels without giving anything away. New channels appear in the interface as they are plugged in, with nothing to configure.

Notes from the microsKanner design team, 2007