What's a good way to measure liquid's pressure and/or velocity?

[cave_cat]

Thanks a lot for everybody's answers. Upon some consultation with others I have concluded that this just seems to be the wrong way to solve what I am trying to solve. Sorry about this.

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suppose I have a long thin pipe. There is some liquid inside (probably water, but can add stuff to it if needed). On a certain segment of the pipe I want to measure the velocity and/or pressure of the liquid at various points along its length and feed the results into the computer. Flow of liquid is quite erratic, sometimes changing direction every 30 seconds, experiencing big pressure changes and so forth.

I do not really care about high accuracy (i.e. +- 10% is fine). Time resolution is a bit more important. As long as it sort of gives the general picture and, most importantly, is cheap and easy to build, I am happy.

Questions:

1. how small is a miniature pressure sensor? how much does it cost? can you give me a link to the manufacturer's website? If there are miniature pressure sensors working based on different physical principles, what should I know about them in terms of their advantages/disadvantages?

2. what are the various ways to measure velocity of the liquid using miniature and inexpensive sensors? All I can think up front now is some clever laser shining through the stream onto a sensor on the other side and a magnetic device tracking the motion of iron dust in the liquid. I suspect that both of these ideas are NOT the simplest way to do it and probably are not something I could order from the manufacturer by overnight mail. Not being a trained mechanical engineer, I am basically at a loss here.

Could the experts here please give me some smarter ideas? Is there a miniature liquid velocity sensor that can be bought inexpensively?

Also, in terms of "inexpensively", ideally I want to build it from the start in such a way that the system could eventually be manufactured and sold for $400 or something. I could spend lots of money now (hypothetically, in reality I would need to find it first ) but ultimately I want to use sensors that can be bought in bulk.

3. suppose, through discussion on this thread or elsewhere in private, we figure out which sensors to buy and they prove to be straightforward to use. Does anybody want to try build something like that for me, working under NDA, noncompete etc? How much would such a project cost? How long would it take? Note, for the hypothetical future, if you end up working on this project seriously part-time, I would arrange that you would have a lab separate from your university's, to avoid their IP grabbing policies.

Thanks a lot in advance to all who respond. If you wish to respond privately, please send me an email through the site.

 

[Proton Soup]

here's one way: http://en.wikipedia.org/wiki/Mass_flow_meter

 

[miskol]

Hi,

if there is only a combination of 2 components inside the pipe, u can use ultrasound sensors to measure velocity. since u do not care of the accuracy, u can use cheap op-amps to construct the circuits.

 

[es1]

http://www.flowmeterdirectory.com/index.html
I had no idea there were so many options... I have to believe one of them meets the 10% accuracy for under $400 requirement.

 

[miskol]

Hi,

if there is only a combination of 2 components inside the pipe, u can use ultrasound sensors to measure velocity. since u do not care of the accuracy, u can use cheap op-amps to construct the circuits.

by 2 components i mean liquid-gas components.