It has been a few years, I think I bought mine from a local irrigation company and I can’t remember the name.
For almost everyone I would think they want 1 gallon per pulse. And choose reed switch/gallon (not the photo diode). Meter size would be based on your max flow rate.
http://www.netafimusa.com/agriculture/products/watermeters-m-order
This website shows pricing on some : (might want to google search and compare prices though)
http://www.irrigation-mart.com/default.aspx?page=item+detail&itemcode=FM-36M201T
Note the 3/4″ water meters go from .9-14GPM. Some of my valves are running with around 20GPM and I have a 1″ meter (spec’d to 30GPM. With a larger meter your accuracy down to <1GPM suffers a little.
Here is the 1″ meter:
http://www.irrigation-mart.com/default.aspx?page=item detail&itemcode=FM-36M251T
There are plastic ones too but I recommend the metal ones unless you just want to play with it in the lab and it won’t have to survive outdoors for a while. (metal one’s aren’t much more expensive anyway).
If someone knocks off a sprinkler head or something i usually see quite a few GPM increase (~5GPM) and it’s pretty obvious.
It is a fantastic tool to determine how much money you are spending per zone. I had perl scripts run to output cost of each zone. Then I focused on the most expensive zones first and figured out how to minimize water usage there. The zones on the longest aren’t always the ones using the most water 🙂 It would be great if we could come up with a strategy to capture flow rates, and generate report(s) and alerts . I just tried modifying the write_log function and now I realize I can’t write out a string like I hoped with that (was going to put in the logfile the flow rates). Might create a new function that just logs it and another file I’ll put in for flow rates for each zone (min and max) so it triggers if it’s outside those ranges… not sure how easy it will be to send out an email automatically or if there is enough memory.
You may wish to keep the protection circuit input to ground (for the flow sensor, from your rain input circuit) since there will be a long wire from outdoors (flow meter) into the OS. There are IC’s out there that could clean up that slow moving signal too. I’ve only been playing with it on the OS device for today but so far it looks repeatable. I compared the flow rate measurement on the OS to the Cyberrain logs I have and they are well within +/-0.3 GPM.
I will probably be installing another OS device and a neat feature would be for it to get the flow rate from the main OS device as an option (I have one pressure regulator and one flow sensor for all of my 30+ zones).