Questions about SeedStudio Water Flow Sensor

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Ramius
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Questions about SeedStudio Water Flow Sensor

Post by Ramius » Wed May 09, 2012 9:20 am

Hi All!
Just a quick question, has anyone used the RB-See-98 water flow sensor as a speedometer for model boats? If so, how would you do the calculations from flow to speed?

Thanks, Ed

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ndk.clanbo
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Re: Questions about SeedStudio Water Flow Sensor

Post by ndk.clanbo » Wed May 09, 2012 8:16 pm

You can probably only get an estimated velocity.
Since its pulse rate is based on the volume of water that flows throught it, and the section is constant, you can see that pulse rate is proportional to the speed.
To determine the proportionality constant you can try a simple experiment:
- place it vertically with a transparent pipe (that must the same diameter of the sensor) full of water connected to it and the other end blocked
- mark the initial water level
- let water flow for a second (or more, if the pipe is long enough) counting the pulses
- mark the new water level

The difference between the two levels, divided by the number of pulses - 1, is the "space per pulse" = K .
So the speed will be "pulses * K / time".

I said it's not accurate because at very low (or very high) speeds, water dynamics might alter assumptions. For example, at very high speed the extra resistance offered by the sensor could make water "prefer" another way, so reducing the actual flow throught the sensor and making you measure a lower velocity. The best way to handle these situations could be to actually measure the number of pulses generated while traveling the same distance at various speeds.

Ramius
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Re: Questions about SeedStudio Water Flow Sensor

Post by Ramius » Wed May 09, 2012 8:40 pm

Thank you ndk.clanbo!
I was just wondering a few things. Does the sensor put out 1 pulse per revolution or more? For if you know the diameter of the wheel and the number of pulses per revolution, could you not just a calculation based upon pulses per minute? Thanks, Ed

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ndk.clanbo
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Re: Questions about SeedStudio Water Flow Sensor

Post by ndk.clanbo » Thu May 10, 2012 1:14 am

Sorry, I don't have flow sensor (yet... maybe in next order, hope to add it to some current sensors as in wish)...
The most probable thing is that it does only one or two pulses per round (isn't it on the wiki page? no... just checked, but you can do some math:
- at 1l/m it pulses at 8Hz, so 1000ml/480pulses=~2ml/pulse;
- 2ml=2cm3 that correspond to 1 pulse
- 2ml are about 1,2cm in a 1/2" pipe (if I didn't mess up something).

So, given the flow into the sensor is equal to the flow around the boat (strong assumption!), for every pulse it advanced about 1,2cm.
Check actual figures 'cause I'm quite tired and I could have done something wrong!

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