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In article <1990Oct4.181312.27021@xn.ll.mit.edu>, tj@juno.ll.mit.edu (Thomas E. Jones) writes:
> I'd like to find references on design criteria and the formulas
> related to hot wire anemometers.  Also, any sources of ready made
> hot-wire anemometers would be appreciated.

	Offhand, I don't know of a specific reference to design criteria
for hot-wire anemometers.

	Hot-wire anemometers are not difficult to design and build,
provided that you have available to you a standard against which to
calibrate and evaluate performance of your design.  For maximum accuracy,
and repeatability I would recommend a standard such as a rotary vane
anemometer, as opposed to a pitot tube arrangement.

	You will learn a great deal after building your first circuit
and comparing its performance to a standard under varying flow conditions.

	The simplest hot-wire anemometer employs a 4-arm bridge circuit,
with excitation provided from a constant current supply, and with
one arm of the bridge being the hot-wire element.  The bridge error
signal is proportional to the fluid velocity.

	An alternate version uses a hot-wire element that has intimate
contact with a temperature sensor.  A bridge circuit with an error
amplifier fed back to the bridge excitation runs the hot-wire element
at a constant *temperature*, with the adjusted excitation voltage
being proportional to the fluid velocity.

	In simple terms, the convective heat loss of a hot-wire anemometer
element is proportional to the square root of the fluid velocity.  One
can vastly simplify hardware design if linearization and calibration can
be performed by a microprocessor.

	There are various vendors of commercial hot-wire and hot-film
anemometers, such as DISA Electronics and Kurz Instruments.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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