Autosteam wands are perfect for locations without training programs. They are standard equipment on superautos - just push 2 buttons and you have a latte.
They have no place or use in a quality-focused espresso bar.
We had the prototypes back in '99. They've probably changed since, but IIRC this is how if worked -
There is the normal steam valve up front, and a second electro-mechanical valve just after the boiler outlet. There is a sensor on the back of the knob that detects the knob position, and when it's opened, the EM valve is opened as well. Then once the preset temperature of the milk is reached, the EM valve is closed by the CPU. There is an NTC (negatively charged thermocouple) probe that's in the milk with the wand that communicates the milk temp to the CPU.
This is also how the Mastrena works. And probably every other machine with this feature.
It really has no bearing on the quality of the steamed milk. Barista competence, size of steam tip orifice and pressure have more to do with that. All it does is shut off the steam at a preset temp. I can tell you that they can be a service issue. The major problem being that baristas get lazy and leave the milk in the wand for extended periods after the wand has shut off. And this leads to a clogged wand. I probably clean 10-15 steam wands a week because of it. This is also somewhat dependent on the shape/size of the pitcher.
Sure thing Alex. I think I was incorrect on one part of the operation, in that you probably have to push a button to activate the autosteam feature prior to steaming. So, in that you can bypass the feature by not pressing the button.