[time-nuts] Weather/units question for European members
namichie at gmail.com
Sat May 24 01:49:25 EDT 2014
There is a great sonic anemometer in:
"An inexpensive sonic anemometer for eddy correlation" G.S.Campbell and M.H.Unsworth, (1979), Journal of Applied Meteorology Vol 18, August 1979, Pp. 1072-1077.
This unit uses 4000 CMOS, a LM301A and two cheap ultrasonic transducers. It operates a phase-locked loop and alternately uses the sensors for transmitter and receiver, swapping ends at about 74 Hz, to get a two way signal. This method cancels most errors. It has temperature and velocity outputs.
cheers, Neville Michie
On 24/05/2014, at 11:16 AM, Mark Sims wrote:
> I am building a weather sensor that includes a ultrasonic anemometer to measure wind speed, direction, and air temperature. It uses 4 cheap ($1 each) HC-SR04 ultrasonic rangefinder modules that output a pulse width proportional to the time of flight of the sound signal (topic is time nut related since it simultaneously measures the speed of sound in 4 directions to a pretty good accuracy/resolution using a cheap-ass microprocessor - ATMEGA328 (like and Arduino)... and does so without using any counter-timer channels).
> Now the question... I would like it to be able to output data in imperial or metric units. In what units is the typical wind speed reported (meters/sec, km/hour, ?). Also air pressure (millibars/hectopascals/pascals/?).
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