Electronic Cistern Water Level Monitor

[hwp]

Anyone know of a manufacturer/distributor of an electronic cistern water level monitor? I would like to mount a sensor on the underside of the trap door for my cistern and have a monitor is a different area of the house. I would prefer to have a monitor that provides a continuous readout of the water level in the cistern as well as a low water level alarm. The only thing that I can find that comes close us a unit made by Aquatel (www.aquatel.co.nz) in New Zealand. But it doesn't quite do what I want

[hwp]

I just found a US company that makes a liquid level sensing system, Automated Sonix Corporation (www.automatedsonix.com). Its systems are not remote but are a possibility.

[Pat]

My basement septic system uses a holding tank with a level sensor that is an aneroid pressure sensor with a plastic tube in the liquid. The sensor is not submerged just the plastic tube. This gives switch closure when the level reaches a predetermined depth (pressure.) This sort of arrangement would work for any liquid that didn't melt the plastic tube or whose fumes weren't highly corrosive (acids etc.)

Patrick [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img]

[hwp]

Thanks Patrick. These are a number of pressure tube systems available. I would really prefer to go with a electronic system. It turns out that Automated Sonix only makes units for commercial applications and are not suitable for domestic systems. So at the moment my best alternative is Aquatel in New Zealand. The neat thing about the Aquatel system is that thre are no wires, tubes, etc - just a sensor/sender and a monitor. But it is not continuous readout since the monitor uses LEDs not a digital LCD readout and there is no low water level alarm. So I'll just keep looking.

[Pat]

Are you handy with electronics? If you have or install a "sight tube" it isn't that tough to make a level alarm or readout.

One basic idea is a LED and a photo diode receptor pair (or pairs.) The trick is to align the transmitter and receiver pair so that the index of refraction of the water vs air (water in light path vs air in the light path) causes the light beam to "hit" the receiver diode or not depending on whether the tube where the light passes is filled with air or water.

This will give you an indication when the water level goes below the set point. Additional pairs can give fractional indications likek 1/4 full 1/2, 3/4, etc. The output of the receiver diode can cause a led to light up so you know the level.

Another technique is to rely on self heating of a diode junction biased in the forward direction. You can do this with a thermistor also. In either case you put the temperature sensitive element (encapsulated in epoxy or similar) in the liquid to be measured and a matching one in the air next to the tank in an enclosed container and insulated from air. The self heating of the (lets say thermistors) unbalances the bridge circuit because the immersed in liquid component is cooled by the liquid. If the immersed component is uncovered as the tank level falls the bridge balance shifts and can be amplified to light a light or ring a bell or whatever.

Another way to do the deed is to get one of the ultrasonic distance measuring kits or an ultrasonic "tape measure" and direct the beam at the surface of the liquid. You should be able to remote the transducer so the readout doesn't have to be in the tank.

There are jillions of ways to automate a level alarm.

You can put a float in the tank and run a string from it over a pulley to a hanging weight. The weight will move up and down with the water level. This motion and weight position can be used to indicate tank level. One way would be to have the weight drive a potentiometer that varied the current in a meter circuit or fed a circuit set to trip at a given voltage (analog to depth.)

... and on and on and on if you are handy with electronics or live near a ham radio guy or similar.

Pat [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img]

[CJDave]

[img]/forums/images/icons/tongue.gif[/img] As i'm sure you have discovered, a great many of the liquid level sensors use electric current to make the connection. Rain water is usually too pure for those to work, unless the secondary voltage is above 350-400 volts. Pat's system with the aneroid is better for rainwater. I have used sight tubes for this purpose and just taped one of those magnetic switches that burglar alarms use to the sight tube. Then we floated a piece of dowell in the tube with a magnet imbedded in it to trigger the switch. [img]/forums/images/icons/tongue.gif[/img]

[hwp]

Thanks for the comments. Our cistern is under part of the laundry room of our house and it has a 8" concrete ceiling. While it would be possible to drill a hole through the concrete between the laundry room and the cistern, I would prefer not to do so. This rules out pressure gauge and mechanical float systems. If all else fails I may try to rig my own ultrasonic system but I have now found a unit called Rain Alert (www.rainharvesting.com.au/rain_alert.asp) made by Rain Harvesting Pty in Austailia that seems to do what I want. One issue with it is that the monitoring station uses 230VAC but I think I should be able to run a 230V circuit to an appropriate location. I am going to find out how much they costs and whether or not there is a NA distributor.

[speedbump]

I'm wondering if the 230 volts is used simply because that is what they have in the country. We are one of the few countries I know of that even uses 115 volts. Most electronic circuits run on voltages in the single digits, so maybe simply changing the voltage regulator would be the answer.

bob...

[bobkrack]

<One issue with it is that the monitoring station uses 230VAC but I think I should be able to run a 230V circuit to an appropriate location. I am going to find out how much they costs and whether or not there is a NA distributor.>

hwp,
If the device you are looking at will do the job for you, I would think you could get a small 115/230 transformer for considerably less than running a new circuit?
Bob

[Pat]

Dave, GOOD ONE! I was having flashbacks to the measuring the height of a tall building with an aneroid barometer thing. There are just lots of ways to sense water level.

I like your reed switch thing a lot. By adding more reed switches you could get a readout to whatever granularity you wanted. Circuits to "latch" the switch closure would be real easy to do. Otherwise as the level passed a given switch it would light its corresponding indicator but only at or very close to that level and no indication of what levels had been passed. You'd have a reset switch to put all the lights out and then as the magnet passed each switch that light would come on and stay on thanks to the latching ckt. IF I couldn't do this for $20 I'd have to turn in my DIY lisc.

Patrick [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img]