Re: Controlling water volume applied

RG wrote:
I need help automating a process we have done by hand over the past few
years.
We need to "spray" tap water into a material mix at different
rates. The typical volume of water applied ranges from 25 ml to 1000
ml. The typical flow rate should be approximately 100 ml per minute.
The accuracy does not need to be that great, probably less than 5%.

We have done this in the past using an approximately 15 psi pressurized
clear plastic column filled with water having a scale affixed. We
would turn the valve on and off manually after monitoring the volume
change on the scale.

I need to automate this process with user defined volumes of water
applied. I have very little experience with control systems and am
looking for as close to "off the shelf" as possible.

I had thought of using a flow meter and a timer hooked to a solenoid.
If I knew the flow rate I could calculate the time to achieve the
desired volume and set the timer to activate the solenoid when the
calculated volume has passed. But I would need to add a regulator to
verify the psi applied to the system is always the same.

I also have thought of using a micro totalizer to do the same job but I
don't have any experience with these devices.

But I basically need a technician to enter the volume in ml and hit
start.
Any ideas on how I can accomplish this task economically?

Closed-loop control may be more sophistication than needed. One or a binary series of (relatively) inexpensive flow-control valves can be selected in parallel to set the rate, and your timer-solenoid combination to set the total amount. So long as the pressure is within rating (say 25 - 125 psi) inexpensive valves will hold to about 10%. They are better over a narrower range. A pressure regulator off the mains set to 25 or 30 psi should make the bank very repeatable. The valves at http://www.plastomatic.com/fc.html have too much flow for you, but I'm sure you can find others.

Jerry
--
Engineering is the art of making what you want from things you can get.
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