Acoustic Resonance Anemometer Design Guidance/Review

[Qeynes]

As part of physics course we get to create our own projects on the arduino, so I'd thought I'd make a combo temperature, wind speed, and wind direction sensor . 
Attached are a top and horizontal view of the ultrasonic transducer and cavity plate design, as well as a tentative block diagram of the sensor circuitry.

The idea is to control a vertical standing wave and a horizontal traveling wave with the phase loop circuit.  To get the loop to lock in quickly I will "kick" the system with a 40 kHz signal from the arduino, which is a resonant frequency of the cavity at about 72 F.
The X & Y transducers will measure the horizontal travelling wave, and their signals will be compared to the signal of the transmitting transducer with the phase detector.  From the phase shift, I should be able to determine the wind speed along each axis for a given temperature, and I should be able to determine the temperature with the resonant frequency.
I plan to use 3 C4046s, 1 for the resonance PLL and 2 for the phase detectors.

My questions:
--What is wrong with my current block diagram?  (There must be something)
---Should I change the way I kickstart the resonant loop?
--How would you recommend I design the low pass filters, because I have absolutely no idea.  It would be great if someone could point me to some tutorials/resources for this.
--Should I introduce some sort of delay between the transmit transducer signal and the signal used by the phase detector in the resonance PLL?
--Is my choice of PLL IC a sufficient for these purposes?

Any help appreciated.  Thanks.

[Docedison]

I can't respond to the physics but I can tell you to use the 74HCT4046 or better an 'old' signetics NE561 or 2.
The CD4046.. even the "BE" versons had VCO's that had stability issues because VCO power supply. The 5V HCT4046 had  a better more stable VCO but If I could find them I'd use NE/SE561's.
Back in the 60's I was making SCA decoders (Secondary Audio Channel) and the NE 561'a or NE567's with some extra effort were more stable and easier to  use then CD4046's.

Bob

[Grumpy_Mike]

I am very dubious about the whole physics of the project.
You are only using one phase locked loop and I don't see where that gets you. Drive the transducers with a differential signal not a single ended one.
Normal wind vectors are measured by three othagional paths and a time of flight, with temprature measurement sepratly as an adjusting factor.

[Docedison]

I just had a maybe crazy idea but what of a pair of iron rings (pole pieces) perhape 25 cm in diameter with hall effect devices in the gaps between ends of the iron rod or heavy wire. If the two rings with sensors were placed 90 deg apart and had sensors in the gaps then the algebraic sum of the two +/- 2.50V signals would give the direction with a suitable vane and speed by the repetition rate or rotational speed of a small rrere earth magnet suspended inside the rings. I plan to use Allrgro A1302 ha ll effect sensors as they have a linear +/- 2.5 dc output signal for varying magnetic fields where the output amplitude shifts with field strength and the the polarity with the polarity of the magnetic field
In other words there will be a "Phase difference" or voltage differential between the sensors that will create an average alternating current voltage equal to the angular difference between some reference point and the wind direction as fed back by the vane and the speed at which the AC is generated (Wind Speed) is the frequency of the returned ac voltage. Much like a magnetic version of an optical rotary encoder.

Bob

[greywolf271]

As part of physics course we get to create our own projects on the arduino, so I'd thought I'd make a combo temperature, wind speed, and wind direction sensor . 
Attached are a top and horizontal view of the ultrasonic transducer and cavity plate design, as well as a tentative block diagram of the sensor circuitry.
++++++ snip+++++

You do realise this has been done and has extensive documentation on the internet ?

[Qeynes]

I can't respond to the physics but I can tell you to use the 74HCT4046 or better an 'old' signetics NE561 or 2.

Bob, thanks for your reply.  After reading your suggestion, I ordered 3 of the CD74HC4046AE from Digi-Key, but only now noticed that they were the CD74HC4046AE, not the CD74HCT4046AE.  Do you know if there will be a significant performance penalty because of my mistake?

I am very dubious about the whole physics of the project.
You are only using one phase locked loop and I don't see where that gets you. Drive the transducers with a differential signal not a single ended one.
Normal wind vectors are measured by three othagional paths and a time of flight, with temprature measurement sepratly as an adjusting factor.

    Thanks for your advice on driving the transducer.  I've attached an updated block diagram which I believe corrects that particular error.  I would be very grateful if you could take a look at it to check if I altered the diagram correctly.
    Much of the inspiration for this project comes from this https://docs.google.com/a/google.com/viewer?url=www.google.com/patents/US5877416.pdf patent.  According to the patent, creating the vertical standing wave is very helpful in increasing the amplitude of the signal and thus helpful in increasing the signal to noise ratio.  I also worry that if there is no standing wave the reflections from the cavity walls will start to mess with the signal.  That's why I have that single PLL controlled by the transducer directly above the signal transducer.  I think it will compensate for temperature effects on the speed of sound when setting the frequency that will make a vertical standing wave (at 72 F the 4th harmonic of the cavity is 40 kHz, but the harmonic frequency changes with temperature).
    One of the primary objective of this anemometer is for it to be small, so I decided to forgo the 3D wind vectors to make the system more suited to for use on a mobile robotic platform.  Once again, thanks for your advice.

[Qeynes]

You do realise this has been done and has extensive documentation on the internet ?

Well, I have seen, for example, carl47's amazing project. http://arduino.cc/forum/index.php?topic=53569.0


However, while carl's project and the others I have found like his are excellent as stationary weather stations, they are quite bulky and operate on different principles than the anemometer described in my previous post's patent reference.  In fact, my attached transducer layout looks fairly large relative to comparable commercial sensors, I now plan to halve the distance between signal transducer and the x&y transducers to 2.605 cm.   I failed to mention in my initial post that the the anemometer is intended to be able to be used on mobile robotics platforms (sorry), like one used by the Olin Sailbot Team (to which I have no connection):


To date, the only documentation I've found of such sensors has been the patent, this simplified manufacturers explanation:
http://www.fttech.co.uk/acu-res-technology/,
and pages 6 and 7 of this paper on robotic sailbots:
http://cadair.aber.ac.uk/dspace/bitstream/handle/2160/3103/IRSC.pdf?sequence=2.
It was that last link that really gave me the confidence to pursue this route; they appeared to get fairly decent results for with a rudimentary phase detector and without adhering very strictly to the patent description.   I hope that by following the patent more closely and using ICs designed for phase detection I'll achieve similar and maybe better results.

If you know of some documentation that augments the 3 links that pertained to acoustic resonance anemometers, as opposed to simply ultrasonic anemometers, I would love to hear it.  I was getting close to using bing to get find information.

[greywolf271]

If you know of some documentation that augments the 3 links that pertained to acoustic resonance anemometers, as opposed to simply ultrasonic anemometers, I would love to hear it.  I was getting close to using bing to get find information

As a matter of fact !!!!...........
I have been looking at stationary anemometers myself for a number of weeks and this is a fairly good link I came across.
Now I have not checked the majority of your links that you placed on this forum, I'm just (trolling !) through these forums looking for other information and happened on your question by chance.... so if you've already come across this reference, sorry for wasting your time....

http://www.technik.dhbw-ravensburg.de/~lau/ultrasonic-anemometer.html