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PIC-Based Water-Tank Level Meter; Pt.1

Looking for a water tank level meter that's easy to install? One that's accurate but doesn't need a complicated in-tank sensor? This PIC-based unit uses a pressure sensor to monitor water level and it displays tank level at the press of a switch. It can also send its readings to a base station with an LCD readout via an RF link.

By John Clarke

Rainwater tanks are now all the go! Australia is one of the driest continents on Earth and faced with ongoing drought conditions, Australians are now rethinking the way water is managed.

In most parts of the country, dams have been at their lowest levels since construction and many towns and cities now have some form of water restrictions. Saving water is vital and using rainwater tanks to store otherwise wasted rainwater is becoming commonplace.

One traditional problem with water tanks is checking how much water is in them. That’s because they are opaque and they are made that way to protect the water from sunlight which would otherwise promote algae growth.

Trying to look down through the water inlet into the dark interior doesn’t help much because this is invariably gauzed over to keep mosquitoes out. And although some large concrete tanks have a manhole, this usually takes some effort to remove, so it’s not a convenient way to check the water level.

Add-on devices

Many ingenious devices have been developed over the years to show the water level in tanks. These include simple passive indicators that use clear tubing as a sight glass, mechanical floats and pulleys that move up and down with the water level, and the more complex electronic gauges.

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Fig.1: in its most basic form, the Water Tank Level Meter is a standalone unit that sits next to the tank. The water level is sensed using a pressure sensor connected by a plastic tube.
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Fig.2: the telemetry version transmits its reading to a remote Base Station which can display a range of data. A solar cell panel recharges an internal NiMH or Nicad battery.

Each has its advantages and disadvantages. For example, sight "glass" systems, although simple, eventually become impossible to read because of algae growth and discolouration of the transparent material due to minerals in the water. And if the tube is directly exposed to the sun, it tends to become brittle.

Similarly, mechanical float and pulley systems require regular maintenance otherwise they become jammed. In addition, none of these mechanical gauges easily provide for remote monitoring.

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