>The basic meter was a high flow tube (that carried the bulk of the
>actual volume). In parallel with that was a much smaller tube, which
>carried anywhere from 100 to 1000 times less volume. It was a simple
>matter to heat the smaller tube at one end and then to detect the
>temperature difference about 1 inch downstream.

This is the principle used in the Helium Gas flow meter I mentioned earlier 
in the thread. The manner of heating the measurement tube was a little 
different though, in that the smaller tube was copper, and fed from the 
secondary of a step down drive transformer, so the tube acted as a short 
circuit (or close to it) on the transformer, thereby getting heated from the 
current through it. The copper tube also formed one of the metals in the two 
thermocouples IIRC. It always seemed a real strange arrangement, but it 
works. 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist