Water Level Sensor
mmoreland
Posts: 89
I'm looking at Parallax's eTape Liquid Level Sensor, and I wonder what folks think of using it to sense water depth in a well. It would be used to detect presence or absence of water at the lowest pumping depth in order to prevent a submersible pump from pumping out all the water and running dry.
I'm designing a ground source heat pump system using two wells as in a Standing Column Well system. Water will be pumped from one well through the source coil of the heat pump and be exhausted into the second well. When the first well has been pumped nearly dry, and here's where the depth sensor is needed, the first well pump will stop, and the second well pump will commence pumping water back through the heat pump until the second well is exhausted, and the process will repeat as long as heat is demanded from the heat pump. I'm beginning to design the circuitry for a controller, but it's necessary to have water depth detectors, and I wonder if the Parallax sensors would work in this situation, or is there a simpler way to detect the presence or absence of water in a situation such as this?
Any thoughts?
Michael Moreland
Mendocino, CA
I'm designing a ground source heat pump system using two wells as in a Standing Column Well system. Water will be pumped from one well through the source coil of the heat pump and be exhausted into the second well. When the first well has been pumped nearly dry, and here's where the depth sensor is needed, the first well pump will stop, and the second well pump will commence pumping water back through the heat pump until the second well is exhausted, and the process will repeat as long as heat is demanded from the heat pump. I'm beginning to design the circuitry for a controller, but it's necessary to have water depth detectors, and I wonder if the Parallax sensors would work in this situation, or is there a simpler way to detect the presence or absence of water in a situation such as this?
Any thoughts?
Michael Moreland
Mendocino, CA
Comments
If space is very tight you could make it from 1/2 inch pipe as long as you make the magnetic float small enough to fit inside with enough clearance to move.
PS the tube surrounding the float needs to be one piece to keep the float from hanging up, so the straight connector needs to be sanded/filed inside so it slides over the 3/4 inch pipe.
Another thought from another point of view: If I hung one wire that was always submerged, that is it extended below the sub pump level or was attached as in the grounding screw to the sub pump, and a second wire with an exposed end or an electrode of some sort that was suspended a few feet above the sub pump intake, would it be possible to detect a change in resistance between the two wires when the water level dropped below the upper wire or electrode, so it would set in motion commands that would turn off the sub pump?
http://www.ebay.com/itm/5m-Cable-Throw-in-Type-Liquid-Level-Transmitter-Level-Sensor-Level-Transducer-/170924210980?pt=LH_DefaultDomain_0&hash=item27cbe07b24#ht_776wt_1236
I`ve ordered one myself for measuring depth i my dam for my micro hydro-powerstation. Have not got it and tested it yet, but I think it`ll work.
This one can measure down to max 5m depth, but you can get transmitters that measures over a hundered meters down. Not sure what depth we`re talking about in your project?.
As I said; just an idea.
This is a lot like my initial thought after reading your top post. What about a stick/pole/pipe with two wires which are bare at the ends. Stick the pole down to level to be monitored and test the resistance. The hard water of many wells should be enough to trigger a significant change in conductivity between the wires submerged and unsubmerged states.
One of the problems with the wires is the need from some sort of ADC to monitor them. You'll also need to figure out a couple of calibration points for the wet and dry values. It sure seems like kwinn's reed switch idea is more straight forward.
BTW, Is there anything kwinn hasn't done? It sure seems like he has experience in just about every field brought up on these forums. I myself have learned a lot from his posts.
You described it perfectly in the first paragraph. The problem with standard float switches is that they need space to swing and can get hung up in tight or cluttered spaces. This avoids those problems. Since your well is so shallow it might be simpler to keep the float assembly separate from the pump pipe by putting a weight in the bottom of the assembly and hanging it on the side of the well pipe. That way any repairs that might be required would not involve pulling the pump up.
The idea of measuring resistance would probably work, but it is more complicated than a simple on/off switch.
Thanks Duane, that's very flattering, but there's lots and lots of stuff I don't know. Most of what I have learned comes from meeting a lot of very smart people while working on their equipment. Nothing like working on computers and electronics to get exposure to a wide range of fields.
BTW, your idea of using two wires and measuring the resistance would work for both measuring actual depth and as an on/off signal. An ADC would be needed to measure the actual depth, and a comparator is all that would be needed for on/off control.
The code is in forth, but you can probably get an idea of whats going on and do similar in spin.
http://code.google.com/p/propforth/wiki/Logger1SR04
Are you still working with the BASIC Stamp? Chapters 5 and 6 of the old Stamps in Class Applied Sensors (aka Earth Measurements) are about measuring water level with a conductive probe, and then putting it in a feedback loop to control water level.
I like Kwinn's scheme a lot. Other techniques for detecting water level take advantage of high thermal conductivity, or electrical capacitance, as water covers a probe, or the acoustic resonance of the pipe, or the weight of the water on top of a pressure sensor.
BTW, How's the solar tracker working out? Getting enough sun there on the coast?
Madison offers a good selection of level sensors and float switches. If you're not opposed to buying and off-the-shelf product, they would probably have what you're looking for.
I'd like to offer one small suggestion. Assuming the wells in question are private wells and not a public water utility well, you're not required to perform a draw-down test on either of the wells. If you can afford to do them, I'd strongly recommend doing so. The information you gain from the test is invaluable to you, as well as to the environment.
Using one source and one sink, you will be drawing one of the wells down when the other is filling. The draw-down test simply let's you get verified flow rates that are attainable from each well over a 24 hour period, with rates given at each hour of continuous draw-down.
Having said that, you will "treat your water table" better if you don't draw the well down too low. In a typical standing column well type system, you're really not depleting the water table (source) of the well because you're pumping out of the well (from the bottom), then dumping right back into it (at the top.) So the only loss in head you have is from the capacity of the system, when the working fluid is in transient.
It would be better for the eco-system AND your geothermal system to draw short intervals from each well. This minimizes possible collapses in the well cavity (near the actual pump) which in turn minimizes disturbances, and thus silt/sand/whatever from being pumped into your system. If it's a deep well in bedrock, this probably isn't a significant issue. Otherwise, you'll have serious fouling from detritus.
Thermally, your performance should be better when you draw from one well for an hour (just an example time period) and then reverse and draw from the other for an hour... but I'm not completely sure about this- it's a complex issue, as you know!
I guess that's my long-winded recommendation of saying "Don't worry about a float switch. Just draw for an hour or two from each well, then reverse flow." Of course, this is only if you're going to be pumping from the bottom of the well and discharging to the top of the other. If not, may have to get rid of your check valves or foot valves on each well pump (depending on construction) and that could cause all sorts of fun priming issues and whatnot.
Good luck!! Please keep us posted, I'm really interested to see how this turns out for you!
The solar tracker is working perfectly (I shouldn't say such things and temp the gods), and it's kicking out the kilowatt hours. We're getting a little too much sun here on the coast lately and sorely need some rain, but thanks for remembering and asking about the array. The results of all that teaching you and others did for me have had a lasting result. Of all the connections I've made online and otherwise, this forum gives me hope for the world!
I will look into your suggestions and, no doubt, be back on the forum asking for help. mm
I intend to perform draw down tests on both wells just so I can have a better idea how much can be safely drawn in an interval such as you describe.
I'm mainly on this forum to get help in designing and building a controller for the pumps and a motorized 3-way valve, but I'll also post information as I discover it regarding the project as a whole. mm