Help with water speed please

[Ramius]

Hi all!
I wish to measure the speed of my sub in the water. I am told that a MS4514 sensor with a part number of MS4515-DS-5-A-002-G-P should be a good choice (?) with a range of 0-2 psi. My guess is that with a 10-bit external A/D there should be a decent number representing speed. I know to use "long" as part of the program what I do not know is what formual to use to do the calculation since this is in water and not air! Thanks in advance for any and all assistence!

Best, Ed

[Acetronics2]

Hi, Ed

is that what you were looking for ???
http://www.engineeringtoolbox.com/pi...bes-d_612.html
and
http://docs.engineeringtoolbox.com/d...ocity_head.pdf

so you can check if your sensor range matches your speed range ...

Wish you a Merry Xmas and a Happy new Year.

Alain

[Ramius]

Thank you so much Alain for the links! To be perfectly honest my math skills are not good enough to write the formula so a PIC can process it.

Hope you and your family and friends also have a great Christmas and a Happy New Year!

Best, Ed

[Acetronics2]

Hi, Ed

as the speed range will be limited ( even for Red October !!! ), I think you'd better use a retrieve table plus linear interpolation.

the 32 bits square root calculations needing too much CPU time ... for the expected result
( and I hope your sub' not used in sea water or "not so clean " water ... you might use a different density coeff : http://www.csgnetwork.com/h2odenscalc.html )

may be you also could have a look for a possible temp coeff use ...

Wish you all the best
Alain

[Ramius]

Thanks Alain!
I do have and can add a seperate temperature sensor for the same PIC and the sub only run in swimming pools, ponds, and lakes with clear water. According to the fine fun folks at Eagletree systems I could never reach the top speed in water as the 0-2 psi range is for airplanes and speedboats. They use a "strange" calculation method they do not wish to disclose. Good catch by the way! My sub is very close to the sub used in the movie "The Hunt for Red October" which is a Russian Typhoon! So what would the caculation code look like?

Best, Ed

[Tobias]

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[Acetronics2]

Hi, Ed

Hope your speedo just is here " for the show " as its lack of precision never will allow any usable positionning info ( through math. integration ).

BTW you already DO have your formula @ #4 ...

Alain

[Ramius]

Hi Alain!
Thank you and Happy holiday's! The only way to work with positioning would be limited to the surface with the use of GPS. The catch is that once you are underwater, GPS is useless. http://www.eagletreesystems.com/inde...product_id=131 shows their boat speed sensor. As for a formula I think maybe you meant the formula referenced in #2? Again my math skills and understand of how the math works is seriously lacking especially when trying to even begin to write the code for a PIC.

Best, Ed

[Acetronics2]

Hi Alain!
Thank you and Happy holiday's! The only way to work with positioning would be limited to the surface with the use of GPS. The catch is that once you are underwater, GPS is useless. http://www.eagletreesystems.com/inde...product_id=131 shows their boat speed sensor. As for a formula I think maybe you meant the formula referenced in #2? Again my math skills and understand of how the math works is seriously lacking especially when trying to even begin to write the code for a PIC.

Best, Ed

Hi, Ed

you're right was @Post #2 ...
If I'm right ... you're begging for the full PBP calculation ...

Sorry, but I won't be able to take care of it before next year ... as I'm the WHOLE family cook for the moment.

Please, Understand it needs ... a little amount of time, as a retrieve table has to be calculated , and you need the full working subroutine ...

BTW ... knowing which processor you use could be necessary ...

Alain

[Ramius]

Hi Alain!
Thank you please take care of the family first. I will not even have a sensor to test until after the first of the new year. Probably a MCP3202 A to D and an
18f1320 although I am open to any and all suggestions. I can test the sensor in a tub of water much like part of a wooden barrel with an arm that spins the sensor in the water and there is a stop watch with a switch to start and stop the stop watch for the time part. I have 6 different speed for the motor that drives the arm that spins just above the water with just the sensor pick up tube in the water. I hope you and your family had a great holiday and that everyone will have a happy and prosperous new year!

Best, Ed