Flow measurement questions

[Huckleberry]

I'm casting about for ideas regarding digital flow rate measurement for wb testing. There are a number of methods, each having its technical and cost advantages/disadvantages.

Here are some of the types I stumbled on, are there any others that should be considered?

turbine
magnetic
ultrasonic (doppler vs. time-of-flight)
vortex
coriolis
pressure differential

Any relevant observations or experiences?

[bigben2k]

Because the availability of different pressures is going to be limited due to the choice of pumps, a lot of these meters are going to restrict your testing ability. It's really not possible to categorize one type of meter for that particularity: you might be able to find something that works well within the types that you've listed, even though they usually offer a high restriction.

A lot of the types you've listed can be fairly expensive, and that would probably become a factor as well.

[BillA]

eh, a bit too general there Ben

magnetic, ignore the rest
1/4"ID flowtube
search Danfoss on this forum for more info
or see my old musings

[Huckleberry]

eh, a bit too general there Ben

magnetic, ignore the rest
1/4"ID flowtube
search Danfoss on this forum for more info
or see my old musings

Does the low conductivity of water affect the ability of the magnetic meter to accurately measure the flow?

[BillA]

read the specs of the model you're interested in
normal water is fine

[Stigma]

I am interrested in the same, beeing able to measure the preassure in of my water system.

I was considering using a simple unit that you can find in many OC webshops:
http://www.microplex.no/rubweb/varer.asp?ARTNR=AC53021
It allows water circulation to be translated to rpm, and input on a regular fan sensor.
More water pr. sec = the turbine spins faster = more rpm.

But, am I correct in assuming that if the turbine spins twice as fast as earlier, the preassure has also doubled? is it linear like that? If so, it would only be a matter of finding out how many rpm = 1psi, and you could easily calculate it from there. You need to have some real equipment to find out the rpm/psi ratio first though =/

-Stigma

EDIT:
Huckleberry, (pure)water is not very conductive, but it IS very affected by magnetic fields. This is because water molecules are polarized (one side of the molecule has a significantly more positive side, and the other has a significanly more negative side). If you've been through basic chemestry, you might remember =) In other words, you shouldnt have problems with water.

microwave ovens are actually based on the whole fact that water is very easily affected by magnetic fields.

[AngryAlpaca]

But, am I correct in assuming that if the turbine spins twice as fast as earlier, the preassure has also doubled? is it linear like that? Flow gets doubled, pressure has to be quadrupled. RPM can't equal PSI as that depends on the pressure drop and the subsequent flow rate etc.

[bigben2k]

Listen to Bill: it works either way, it's all in the manual! The only thing you might have a problem measuring, is peanut butter... ;)

[BillA]

nah, use a screw pump - be ok