Measuring my well depth

[3v0]

Probe construction is tricky, though. Use teflon insulated wire - you wont get muck and slime growing on it (changes capacitance). You should also make the wire fairly rigid (use tension) so that it retains it's shape after you have calibrated.

When the water falls below the probe there will be a change in capacitance. If one looks for that rather rapid change (compared to slime or mineral deposits) then within some limits the actual capacitance does not matter.

No calibration.

 

[ericgibbs]

hi,
I should also be possible to have separate cable loops down the well and wire them as a capacitance bridge, driving an oscillator.

If you just want to avoid emptying the well a float on fishing line to a microswitch and battery/buzzer is the easy and cheap option.

 

[ronsimpson]

My well runs dry in about 1 hour of operation. Then it needs and hour to fill. When I bought the farm there was a row of burned out pump motors from running the well dry.

I went to the lumberyard and bought a “sump pump float switch.” It is a wire with a float on the end. There is a switch in the float. At a point on the wire about 2 feet from the float I clamped the wire to the end of a long pipe. The pipe and float are lowered into the well. If the water is low the float hangs down and the switch is open. As water rises the float tips up and the switch closes. The length of wire (2 feet) sets the distance between turn on verses turn off. To calibrate I ran the well “dry”. Lowered the pipe until the switch closes, then pulled the pipe up until the switch opens. Then pulled the pipe up 6 inches higher. The result is the switch opens when the water is 6” from dry and the switch closes then the water is 2 feet higher.

A sump pump float switch is built to handle the motor current.

My well has a large diameter. If you well diameter is small this will not work. Then you should do what EricGibbs suggested. Put a float on a cable. Tie the cable to a micro switch. The cable must not stretch with time!

Good luck!

 

[philba]

When the water falls below the probe there will be a change in capacitance. If one looks for that rather rapid change (compared to slime or mineral deposits) then within some limits the actual capacitance does not matter.

No calibration.

I dont see how there will be a sudden drop in capacitance. Assuming the water drops at a constant rate, the capacitance will simply reach a floor value. That's the theory, However, since the wire is still wet, it will continue to drop at a much lower rate for some time after the level is below the probe. I would probably use logic like this:

if rate_of_change < THRESHOLD AND pump_running then
    stop pump

You could use this lower value to determine the minimum capacitance. It's not perfect but would probably OK. However, you will have a more difficult time calibrating capacitance per unit of depth.

On the subject of turning off the pump when the well runs dry. There is a much more effective solution that I have for my water vault (8K gal filled by a moderate flow spring). It's a pump controller from Franklin Electric. It senses over and under current situations and shuts the pump off. There's a 30 minute reset (adjustable, I think). It's really nice as it allows me to see what's going on with the pump. In my situation, I run my tank dry on a regular basis and haven't burnt out the pump yet. I'd guess it's gone through around 500 cycles since it was installed. It wasn't cheap but it is very simple and quite reliable.

https://www.franklin-electric.com/Prod_text/M1330.htm

 

[3v0]

philba

You are correct I should have written. It is my week for sticking my foot in it.

When the water falls below the probe there will be a change in the rate at which the capacitance drops. If one looks for that rather rapid change in the rate of change (compared to slime or mineral deposits) then within some limits the actual capacitance does not matter.

There is no need to know actual depth. Just that the water is below the probe which you can find the 'code' you provided.

Yeah I had it wrong but my point is that one need not look at actual calibarted values.

 

[philba]

It depends on what the OP was looking for. If he wants water depth, then the probe needs to be calibrated.

If he wants to know when the water table has dropped to a specific level to shut off the pump, you are right/ Though, he will need to position the probe at a very specific depth - relative to the pump inlet. I think the approach of watching the current draw of the pump motor is a better way to go. No need to accurately position a probe and the electronics can be placed away from the well.

 

[3v0]

This is one of the problems that I like to think about. There are so many ways to solve it. Most are to complex for a one off solution where a float switch would do the job.

If the system uses a pressure tank you could turn off the pump for a fixed period of time when the pressure falls some level below the pump cut in pressure.

You could use any sensing method in conjunction with a micro controller in a attempt to turn the pump off just prior to going dry, and keep it off long enough to provide some desired degree of well recovery. It could provide information like the well water depth and recovery time. Give a general indication of the well health, estimated water usage. Maybe some AI. Very Geeky.

On another tack....

I think Blue Dog mentioned that the well went dry watering the lawn or irrigating. It may make sense to turn off the water to the irrigation with an electric valve (rainbird?) just prior to the well going dry and the pressure dropping. That way there would still be water in the house. Lots of assumptions not in evidence here.

 

[Ambient]

Won't the permeability of the chlorinated pool water be different than fresh water and thus change the capacitance? Or does that have no effect due to using insulated wire? If you use a non-insulated wire the pool water should conduct rather than insulate, so insulated wire is needed. From what I remember you would need to know the permeability of the water and the insulation to calculate the capacitance, so fresh water will change things.

EDIT: and if the permeability of the pool water effects the capacitance you won't be able to calibrate it properly. I may be off, I hated electromagnetic theory.

 

[Blue Dog]

Long week so I'm just getting back to the post, love the ideas. The wire/cap is what I'll try first in the pool (not worried about getting the cal correct at this point, that can be done with software enhancements later) and well water is fairly constant requiring probably only minor seasonal adjustments. If I used a larger dia pvc pipe and put 2 loops at 180deg apart I wouldn't have to worry about gnd issues, correct? Prefer to go PIC than meter- think it would allow some data collection for seasonal level var and longterm impact of approaching suburbia on the aqua.

Switches are simple solutions for control- that's why we play with remotes, micro p's, sensors, timers etc. Most of the posters know the simple way- but what would you learn from that?- look what I've learned so far -from air pump and a pressure sensor system evolving to RCTime calc's and var caps to calibrate- awesome site

 

[things]

there was a post around here to do with something like this, and one of the posts suggested was; a magnet that floats (on something) in the tube with the water level. and run some reed switches down the side of the tube and when the magnet passes it it goes closed circuit then hook that up to anything that indicates where the water level is.

 

[atferrari]

Not to discourage anyone, but Google for "radar" sounding systems in tanker vessels. They not only work; they were approved with safety in mind.

If I were you I would try the US approach with an eventual correction for temperature.