Need help....Water Level Detection

[gscorvette]

Hi,

I am a mechanical engineering senior working on a design project. This project is to create a water dispenser for a disabled person. We need a way to detect the water level in the cup for automatic shutoff or just a program that dispenses a certain amount of water.

I am looking into a PLC unit for this task. What do I need to do and what do I need to get. I need something as cheap and easy as possible.
No one on our team has experience programming PLC units.

Thanks in advance for the help,

Gretchen

 

[Goody]

I wouldnt have thought you needed a plc unless you were going to dispence many different amounts of water. Or, you wanted to teach the machine how much water to dispence.


Surely a relay, timer and solenoid could do what you want

 

[rsdoran]

I imagine there are a variety of ways to do this, one would be to use a valve with a specific amount of flow per second and use a timer to open its valve for the time it would need to fill the cup.
http://www.giplindia.com/pdf/water-valve-catalogue.pdf

I dont have links but they do make valves designed for this purpose I believe, valves that when activate dispense a certain amount of liquid. I will look a little to see if I can locate some.

 

[Tom Jenkins]

Go to Omega Engineering (catalog or on-line). They have a bunch of inexpensive water level detection switches, from simple float switches to the optical type. Most of these are brand labeled from someone else, but unless you are talking a high volume your shopping time is more valuble than the extra mark-up.

 

[Alan Case]

Hi. You can copy what a greek guy called Heron did approx 1900 years ago. (He couldnt afford a PLC) Link. = http://www.smith.edu/hsc/museum/ancient_inventions/hsc18b.htm

Regards Alan Case

 

[Allen Nelson]

If "cheap and easy" is a requirement, then you don't want a PLC.

My dentist has had this sort of gizmo since before PLCs. As far as I know, it's all mechanical. Spring loaded pad under the faucet. Whenthe water level gets to max, spring compression trips switch, closing valve. No cup also closes valve.

The only drawback is that it requires a uniform cup weight.

 

[Pierre]

So your are mechanical E.

Do it mechanicaly then!

No electronic can beat a good mechanical principal.

Volumes or flow measurement and control should be a greast challenge.

 

[Ken Roach]

I was sitting at an airport bar in Detroit last week, trying to get a little sleep-induction going for the long flight back to Seattle.

I noticed that all of the bottles in the bar had identical bulky plastic spouts on then, all sealed with tamper-evident tape.

The bartender had to put a tethered collar that sat in a holster near the soda dispenser around the spout to pour a drink. The collar was wired directly into the cash register.

I presume that the way it works is that each spout is a known diameter, and they have a pretty good idea of the pressure exerted by a bottle full of booze. Therefore if a magnetic field in the collar device, activated by the cash register, causes a check valve in the spout to open for a predetermined amount of time, the cash register has a pretty accurate measurement of the amount of booze that was dispensed.

Now, if such a technology can be cheap enough to deploy at DTW, and accurate enough to make my Scotch watery with melted ice, then it's probably a good way to dispense exact amounts of liquid to quench the thirst of the disabled. Not to mention the fact that it's a great excuse to go visit the liquor supply warehouse.

Coffee vending machines must have a similar circuit... I can punch "12 Oz" on the blend-and-squirt at 7-11 and it won't overfill my cup.

All a "PLC" will get you is an overkill programmable timing relay, and most of those can be had for less than even a tiny PLC.

If you need a programmable timing relay to do more than just the one timing function, look at "smart relay" devices like Siemens Logo, Rockwell PICO, or Klockner-Moeller's smart relay.

Interfacing this relay to your valve will be the only real challenge... time to go make friends with some of the EE's.

I just think the liquor metering devices might come in handy at the party after Finals, is all.

(P.S. Hey Alan... cool dispenser! Does it work with Ouzo? )

 

[chrisatwan]

If you really want to get fancy though you can go with a simple eeprom or flash chip you will have to program it in assembler, but you professor would be impressed.