Measuring water levels

[TideMan]

At our bach (pronounced "batch" - a Kiwi word for beach cottage), we run on rain water and we have a 13,500 litre water tank. I'd like to monitor the levels in the tank and send them by wireless to the house, just like I do with my Fine Offset PWS.

Ultimately, I'd like to build a mathematical model that uses rainfall from the PWS and the roof area to calculate inflow to the tank which I'll compare with the rise in water level to figure out the evaporation and other losses in the system. We'll also be able to calculate our water use.

Does anyone know of a relatively cheap system that can monitor water levels and send the signal by wireless to a base station that can be connected by USB to a PC?

I've found plenty of expensive ones on Google. Some of them use a pressure transducer submerged in the tank and others ping an acoustic signal down at the water surface.

I'm looking for the equivalent of a cheap Fine Offset system.

[steve]

There are devices for wirelessly monitoring the level of oil for central heating systems which may be suitable. For example: http://www.sensor-systems.com/tankgauging.html - but I guess they are the same sort of thing as the ones you've already seen.

That 'Watchman Sonic', for example, costs about the same as a Fine Offset station - here in the UK, at least. There's a similar device made by a company called Apollo. I don't know how you'd connect one to a PC, though; I guess that's where they start getting expensive.

[Gina]

I guess if you were of a "Heath Robinson" disposition (rather like me) you could use a system of float, weight, string and a pulley together with a modified wind direction sensor of a PWS. Use a pulley size such that the float going from empty to full turns the pulley and hence the "wind direction" one revolution (360 degrees).

[hills]

I guess if you were of a "Heath Robinson" disposition (rather like me) you could use a system of float, weight, string and a pulley together with a modified wind direction sensor of a PWS. Use a pulley size such that the float going from empty to full turns the pulley and hence the "wind direction" one revolution (360 degrees).

Interesting concept!! How would you differentiate between the water level falling and rising though?

EDIT: Oh I think I see what you're saying, its one full revolution between empty and full?

[Charlie]

A variation on Gina's theme that I've used in the past to measure which way an antenna was pointing... use a potentiometer and a hobby USB experimentor board that has an A-D input. You can run a lead from the potentiometer a very long distance to get to the USB board and introduce no errors. Not quite wireless, but not too painful either. Any old cable will do - quad telephone wire would be great (3 + spare) or you can use a single pair and a battery at the remote end.

You can also use a cheap analogue voltmeter connected to the same leads that are running from the potentiometer (switched to an appropriate scale and with a new label stuck on) to indicate water level at a glance without the computer.

If you can't find a pulley large enough to go empty to full in a single turn, then you can use a multi-turn potentiometer - 10 turn pots are fairly common.

Lots of devices constructed from "chicken wire and bubble gum" around my house!

[Gina]

I guess if you were of a "Heath Robinson" disposition (rather like me) you could use a system of float, weight, string and a pulley together with a modified wind direction sensor of a PWS. Use a pulley size such that the float going from empty to full turns the pulley and hence the "wind direction" one revolution (360 degrees).

Interesting concept!! How would you differentiate between the water level falling and rising though?

EDIT: Oh I think I see what you're saying, its one full revolution between empty and full?

Yes, that's right.

[mcrossley]

Not wireless as it would require a PC... Find an old computer mouse with a wheel, and drive one axis sensor on that from a float/line arrangement. Count the mouse ticks for a full/empty fall. It would be a relative counter and so subject to slippage errors, but is directional -an has a PC interface and software

If you use a potentiometer as suggested by Charlie you can also use the old Joystick interface to read it directly without having to buy an interface board.