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[Darrell Norquay]

At 08:04 AM 9/10/96 -0500, Mark Pitts wrote:

>>Is there any reason why I can't build my own mass meter wth some nichrome
>>wire, and a foot of 6" drain pipe?

And Tom Cloud replied:

>Okay, can I speculate too??  I know that liquid and gas measurements
>have been made by using a heated wire (or thermocouple).  The concept

This is the way most thermal mass flowmeters work.  Often, they use two
identical thermistors, one in the aistream with a large enough current
forced through it to cause self-heating, the other with minimal current at
the same temp as, but not in the gas stream.  Then, either measure the
resistance difference, or servo the current into the sensor to maintain the
same voltage as the reference, and measure the current.  

I read an application note somewhere about a group that made a relatively
accurate flowmeter out of a couple of #47 panel lamps.  They broke the glass
envelope off one of them (sensor), and put it in the airstream, and left the
other bulb intact (reference).  Force a constant current through the two in
series, and measure the voltage across the sensing element.  This would be
the ultimate in cheep MAF's!  I'm not sure if the reference element was also
in the gas stream, but I know they limited the current to a value low enough
so they didn't burn out the filaments (no light).  Let me know if you try
this, I'd be interested in the results.


regards
dn
dnorquay at awinc.com