7 November 1997

Radio waves link new water monitor to base

UK GROWERS next year could be using an automatic soil moisture monitor, linked via radio to a base station. It is currently being tested in commercial crops of potatoes and vegetables in Portugal this winter.

Developed over the summer by DMA of Emneth, Cambridgeshire and seen at last weeks Water for Farming 97 event at Peterbor-ough, the new station has at its heart a standard data collection and transmitting head from an ADCON weather station. This has a "plug-and-play" facility for a range of new and off-the-shelf sensors.

For example, use could be made of a new moisture sensor on display from Germany which comprises a tensionmeter coupled to a transducer. It converts moisture readings into electronic pulses for transmission. By replacing a mechanical dial it reduces the risk of data being corrupted.

And another sensor, which was developed by the Czechoslovak army in the Cold War era, could also also be plugged in. The Virrib sensor has a 30cm (12in) diameter twin loop of metal covered wires through which high fequency radio pulses are sent.

When in soil the speed of the signal return is slowed by moisture, the difference can be measured to give an accurate idea of the level in the soil.

Strategically sited

The radio transmitter on the DMA soil moisture monitoring station has a range of 12.4 miles (20km), but the signal can be bounced down a line of strategically sited repeater relay stations to the DMAs base station.

Real time data can also be sent via modem down a standard telephone line. The soil moisture measurements are never more than 15min old, so never out of date.

Price of the mast, radio head, and rain-gauge is £1200, with the tensionmeter-transducer unit costing an extra £270. The Czech ring sensor costs a further £180.

DMAs David Martin with radio transmission equipment for soil moisture monitoring.