On Mon, Jul 4, 2011 at 12:55 PM, Joshua Cude <joshua.c...@gmail.com> wrote:
> > > On Sun, Jul 3, 2011 at 10:09 PM, Jed Rothwell <jedrothw...@gmail.com>wrote: > >> >> >>> Nor does the manufacturer's brochure assert that steam quality can be >>> measured with their equipment . . . >> >> >> It said the equipment measures enthalpy. You can't do that unless you know >> the quality of the steam. It also said that the instrument measures by mass, >> not volume. >> >> You really should give up on this claim. The manufacturer makes no claim >> about steam quality. It calculates enthalpy of humid air from the >> temperature and RH. As Driscoll has argued, a capacitance measurement could >> not give steam quality. >> > You're quit right. Either the probe uses a polymer between two capacitor plates that absorbs water and the permeability between the capacitor plates changes accordingly or it measures the permeability directly. If it is a polymer, wet or dry steam makes no difference. The polymer will read 100% humidity in wet or dry steam. If it is measuring vapor directly the increase in capacitance is too high for 100% humidity. So, what's an instrumentation firmware programmer to do in this case? He can either display an overflow condition or call it 100% humidity. Having played the role of an instrumentation firmware programmer yahoo too many times, I would go with the latter choice. Why? The user could very well be using the thing in foggy weather. I still want my instrument to work in fog so I call it 100%. This would be OK. 100% is the humidity in fog.
