air flow measuring using ultrasonic

rakieen

hay guys..
can somebody help me,find circuit related to my final year project (air flow measuring using ultrasonic)..using transit time method..what kind ultrasonic tranduser i can use??why??..is needed i sampling signal from transmitter receiver to measured time flight.. :roll:

the air flow through the pipe only in 2-4second...like air blow from our respitory....


helps me please or sure i die!!!

This was a student project last semester at FH Pforzheim.
For now, I can tell you only the main-idea, next week I can post the whole report.

At this project, there where 2 transmitters and 2 receivers, ordered in a rectangle.
T------R
-..\../...
-.../.\...
T------R
The transmitters and receivers where aligned diagonally, so that the speed in both directions could be calculated.

The circuit is very simple, you need only:
- 2x Transmitter/Receiver
- Schmitt-Trigger
- Microcontroller for time-measurement

The time-process is like this:
- The microcontroller send a short pulse to the transmitter and starts a timer
- The Receiver receives the pulse and (because it is a sine-pulse) puts it through the schmitt-trigger.
- The Microcontroller (in our case a PIC 16F870) detects the pulse and stops the timer. The measured time is has now to be converted to the speed.
- Calculate Speed by knowing the distance between the transmitter/receiver and the temperature (pressure is not that important). The formula has to be looked up, but that should not be that difficult.

If you need more information, tell me.

Don't try to get the speed out of the phase-variance: it seems easier, but you can get problems with overflowing because you get over 360° under some circumstances.
Doubler-Effect will also not leed to the wanted result.
(Both tried out without acceptable result)

The sound speed is calculated by this formula:

v = 331.5 + 0.6 * t [ m/sec ]

where t - is a temperature in Celsius.

So, you will need to measure temperature too.

----------------------------------------------------------------

Hmmm, it is interesting that by two pair of tx and rx we can made non-mechanincal wind meter - it can meausure wind speed and direction by vector calculating:

tx1--------->rx1

tx2
|
|
|
|
|
\/
rx2

Seems it will be useful for home-made meteostation.

Hi

In the EPE mag issue from Aug/Sep 2003 this ultrasonic windspeed measurement is used. Depending upon accepted error and distance between tranducors I do not think you have to measure the temperature. It calculates the difference in speed of sound, running with the fluid/wind or in the other direction.

Take a look at the schematic and code in EPE and if you need you can measure the emperature aswell, I guess you need it anyway since it is a respitory system.

/Cl