Need ideas for liquid flow meter

Has anyone come across a liquid flow meter with a digital output? I have an application in which I need to deliver a fixed (programmable)
amount of a liquid, and any of the industrial solutions I've seen are both bulky and expensive.
I'm thinking something like an arduino board as the smarts, but the key part would be a means to measure the volume of liquid, and send out a signal which can either be read periodically, or if a fully contained batch measurement unit, then send a signal when the amount has been delivered, to allow the controller to hit the relay on the solenoid valve ... or similar ...
Pointers would be appreciated ...
Cheers, Rob.
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    --Try the Omega catalog; might find something there. Their specialty is about every kind of measurement device there is. Last time I looked they had *4* catalogs..
--
"Steamboat Ed" Haas : Never thought I'd live to see
Hacking the Trailing Edge! : our "iron curtain" crumble...
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lefty wrote:

If you're measuring flow rate, look for a venturi flow meter or the like. If you're measuring a fixed volume, a simple float on a toggle switch has proven effective (open the back of your toilet). A digital scale is also good.
- Daniel
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And if you want to control the volume (measuring it was just a way to tell when to shut it off) then there are pumps which will deliver a set amount per revolution, just count the revs. They come in all sizes for all volumes-per-second...
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lefty wrote:

We need more information. What kind of fluid volume are you talking about? Do you want to meter a few drops of liquid into a test tube as part of an analytical chemistry system, or measure water usage in an irrigation pipeline on your farm? How much accuracy do you need? Is 10% good enough? Is the fluid conductive? Viscous? Flammable? Does it matter if the unit reads zero at very low flow rates?
Try again, please.
                John Nagle
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The idea is to measure a fixed volume of *WATER* provided from a hose, to a receptacle within a vehicle, which arrives at the "filling station" for replenishment several times per working day. Currently the process is done manually, and requires a human to stand and watch the process for 10-15 minutes, and we'd like to free up the person for other tasks while the resevoir fills itself. Basically, it would pay back very quickly in terms of opportunity costs ...
Ideally, the amount would be user programmable, the device would fit on a standard 1" hose, and the controller would allow the delivery of a measured amount of water. I'm aware that a timer could come close, but there are many variables which would have to be taken into consideration (pressure, flow rates, time of day vs demand upon the city mains), which could be alleviated by simply measuring the volume through the device, and triggering a solenoid to shut off the flow.
The pump idea is cool, but does not apply in the case of delivery from a hose. Just looking for the ability to shove the hose in the spout, hit the start button, and walk away knowing that we won't be pumping spillage down the drain if the attendant fails to check back ...
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<snip>

If the goal is to add a fixed amount of water each time, then you might do better with a tank, a float switch (adjusted to switch when the tank holds the desired amount), and a couple solenoid valves (or a single three-way valve). This might be easier than measuring/ integrating flow rate. If the amount to add varies (e.g. for different vehicles), or is a huge volume, then this suggestion is likely off-target. If the volume is small enough, elevating the tank would eliminate the need for a pump -- though pumps aren't too expensive.
HTH,
-- Larry
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Thanks, Larry, but the holding tank idea was discarded fairly early on in the process.
The idea is to use a minimally invasive approach to filling a fixed size, albeit movable tank using a hose. Adding a holding tank with float valve etc. etc. uses up too much space budget, as the tank would have to be fairly large. In addition, the capacity of the system would be limited by the holding tank size, whereas a flow based measurement system could be used to batch fill a bucket or a swimming pool, provided that the accuracy is sufficient.
I was hoping that someone was aware of something like a turbine flow meter with a digital output which would say, fire every n units, or every rotation, provided that a fixed volume was passed with each rotation ... then the problem is reduced to capturing the signal, and a simple firmware problem ...
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lefty wrote:

You're working way too hard at this. Just buy a standard gas pump nozzle with automatic shutoff and hook it to the water hose. They're about $50 to $100.
http://www.jmesales.com/department/2019/1/Nozzles.aspx
                John Nagle
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Just as a side note. How do they work. Surely they cant have power running though them. I would have thought there would be to much risk of a spark. I thought may be pressure build up in the nozzle when the end is submerged. Any ideas.
Not very robotic I know, but just a mechanical problem thats been solved and I can't figure out how.....
Thanks     Rob
John Nagle wrote:

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Rob Last wrote:

http://auto.howstuffworks.com/question25.htm
- Daniel
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Thanks, John,
A simple and elegant approach. This might just work, provided the venturi vent and nozzle can be extended into the resevoir ... apparently an experiment is in order 8-)
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