Hello,
Recently, we did a few hydraulic experiment with HydePark ultrasonic sensor to measure the water depth in open channels. However, it seems that it doesn't work where there is a slope(a water fall or dam-break flow were 'disappeared'). Well, the type of the device I used is SM956A-110000 according to the nameplate showed. Will you please tell me how to gain the echo again and measure the distance within a slope zone? Thanks a lot!
Best regards,
Ming XIAO
Here is my guess. In open channels, the flow is subcritical, but steep gradients, cascades, falls probably has some or all with supercritical flow, much turbulence, hydraulic jump in surface, standing waves, much oxygen bubbles and unsteady surface. This equipment probably cannot function properly in these unsteady circumstances or you get alot of noise (fluctuation). Take a movie of the cascade or falls water surface and run it back in slow motion, and you will probably see how unstable it is. The reason we use water surface sensors in streams and open channels is to help estimate streamflow using a developed stage discharge relationship. We measure in areas of uniform or subcritical flow, and avoid supercritical flow due to water level fluctuation and turbulence, etc., and also unsafe and extremely difficult to measure without substantial error. I am not saying to give up, but it may be extremely difficult to do, I would make sure I have some good purposes in mind, and perhaps the difficulty is the challenge.
I am also little confused, not that discouraging
As far as I know, the conventional ultrasonic (or radar and laser) sensors designed to determine the distance to a water surface use the so-called "Time of Flight" (TOF) method: they emit a pulse of sound (or light) and they measure the time it takes for the pulse to reach the surface and go back to the sensor; after that, the distance is computed from the knowledge of the sound speed (or of the light speed) into the air (in practice, the sound speed depends on air temperature).
Therefore, these sensors do not work if their pulses do not go back. In this case, they must be placed perpendicularly to the water surface, because this type of surface reflects most of the sound (or of the light) specularly, i.e. as a mirror.
So, if you have installed your sensor vertically (as usually done), this could be the reason why it does not work where the water surface is not horizontal (e.g., near a waterfall or during the passing of a large wave). In practice, I undertsand that the sensor must look perpendicularly to the water surface with a tolerance of a few degrees.
In addition, and as said in a previous message, the ultrasonic "water level" sensors may fail if the water surface is very agitated or if there is a lot of air bubbles...
For the above reasons, and unless you can consider other types of sensors to monitor the water level into your open channels, a suggestion would be to spread diffuse tracers onto the water surface, such as small paper sheets (of a few cm), hoping that some will be detected by your sensor; but this may be unpractical (if you try, please let me know if it works).
Sorry for the bad idea: when suggesting using paper sheets as tracers, I was thinking of a laser sensor (in case of an ultrasonic sensor with a frequency of tenths of kHz, it should not work).
Hi,everyone
I quite agree with your comment on my issue. Well, actually, we tried a lot of ways to make it. For example, we utilized paper or bits of wood floats on the surface to change the catopter plane. Or we made perturbations uptream the channel. Sadly but true, it doesn't work.
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