Underwater speed?

[Ramius]

Hi Nick!
Thank you and I would not mind a paddle wheel type except they all seem to be really big! I do not believe water density will be much of a problem since I will only be operating in fresh water and for a sensor I am using an MS5541C's which are temperature compensated. What I really do not know is the actual formula for velocity. Water density values seem to be all over the map. Do you know of or have a simple formula I can program into a PIC (PIC Basic)?

Antenna work is almost a "Black Art". For a transmitter your main concern is what is called SWR (standing Wave Radio). Basically you are sending power up a coax and when the power hits the antenna if you have the correct antenna and correct impedence (AC resistance) then none or a very minor amount of power will be reflected back to the transmitter or used to "heat" the coax. On a receiver you have the same problem in reverse where you want all the received signal you can get! A dipole (two wires 180 degrees from each other) has an impedence of 300 ohm. When the two wire are at 90 degrees you are looking at about 50 ohms. It even becomes more complicated with the lenght of the antenna wires! That is full wave lenght, half wave lenght, 5/8 wave lenght, 1/4 wave lenght. It can boggle the mind!

Best, Ed

[Demon]

I was thinking of these. Just need 2 fittings to connect hoses in/out.

http://koolance.com/ins-fm16-coolant-flow-meter

You should be able to make your own controller with PIC.

Robert

[Demon]

Formula for velocity:

Follow sub in a boat at max speed, look at knots on gps, note reading from flow meter.

Half velocity = 50% knots, etc.

Or is that too simple?

Robert

[NickMu]

Hi Ed,

I knew it is not an easy task to get such system going especially when in my application the transmitter will be above and bellow water at times. I will try some other avenues first and if no success I might bother you with some more questions.

I will be away from my office for a few more days so I do not have access to my notes.
For our test we just calculated the speed of the jet and the volume of the water passing through in a time period. With the water density as a constant we were able to calculate the thrust.
In your case I’m quite sure you will need at least your differential pressure, the surface of the sensor (maybe) and the water viscosity. I will look into getting you a formula combining all the factors from which you can extract the speed as the only unknown.

What will be an acceptable size for the paddle wheel? The one I used was a little over 1” diameter and it is used on Sea-Doo PWC for speed indicator. It gives 4 pulses per revolution and it is a completely sealed unit wit three wires interface (power in and signal out). If you are interested I can send you one as soon as I get access to it. Just PM me your address and you will have a possible back up solution.

For the differential pressure method how hard will be for you to take a couple of readings at half and full speed to see if your numbers will make some sense. From that it will only be a matter of coding.

Regards,

Nick

[NickMu]

What you are dealing with is the case of dynamic pressure in fluids. One of your sensors will read the static pressure and the other one will read the total pressure. The difference will be your dynamic pressure. Using the formula: P = q*V² you can extract your speed.
P= dynamic pressure
q= density of water
V= speed
So you have your readings for dynamic pressure and you have your water density (I’m not sure if you have to compensate for temperature again since your pressure readings are already compensated) and you can calculate your speed.
I had the chance to do some Google search and I found this:

http://www.engineeringtoolbox.com/dy...re-d_1037.html

HTH.

Regards,

Nick

[NickMu]

One mistake on my formula:
The left side should be multiplied by 2 or the right side should be divided by 2.

Regards,

Nick

[AvionicsMaster1]

Just sayin', that's what I said. Even used the same link. Compensation for density in same post. Number 18 if you'd care to peruse.

[NickMu]

Avionics,

I can not explain the duplicates of your suggestions in your earlier posts other than I started my input to this topic late and I did not carefully read the posts before my question to Ed about the RC system.
I felt that I should share the little information I had but the last thing in my mind was to take credit for something that you already posted. Ed asked for a possible formula and, without reading the earlier posts, I gave him the best I could find just to repay his generous information exchange about RC system.
Please accept my apologies for that.
If one positive thing will surface from this is that it could be Ed’s best solution since two separate people thought the same solution which is an “engineering nonsense”. You will always have n+ 1 solutions from n designers. Each one has a different solution and the +1 is the one that should be used.

Again, it was just my superficial attention to this topic and I’m sorry for it.

Best regards,

Nick

[Ramius]

Thanks Nick!
If it is 1" is that the body of the paddle wheel or the pipe inlet size? The reason I am asking and trying to keep everything as small as possible is that the bow are is starting to become very crowded as this is where the torpedoes and missles are plus a mechanism to deploy and retract the bow planes!

Ed