Innovation: Time up for steam-age gas meters: Nuala Moran on an electronic device that will prevent fraud

ELECTRONIC gas meters are about to replace the grey boxes that have lurked in stair cupboards for more than 100 years.

Volume production of the electronic meter, which uses ultrasound to measure the flow of gas, begins at Siemens Measurements factory in Oldham, Greater Manchester, this month. British Gas has awarded a pounds 20m contract for the first year's production of 300,000 meters, which will be installed under a running programme of meter replacement. British Gas replaces almost a million meters a year.

The old meters, unchanged since Victorian times, have a mechanical diaphragm that opens up to let a known amount of gas through and then closes, registering a unit on the clock. The electronic meter has no moving parts; as the gas flows through a measuring tube, ultrasonic impulses are emitted from each end of the tube, one travelling in the same direction as the gas flow, and one against the flow. The sound waves moving against the flow take longer to travel through the tube than those travelling with it. This 'time of flight' effect can be used to determine the rate of flow and so calculate the volume of gas used. The meters, which are half the size of their predecessors, are powered by batteries with a life of 10 years.

British Gas says the new meters will make it easier to detect fraud. The built-in computer will provide a record of the meter's activity, exposing any attempt to tamper with the clock. In particular, the practice of swapping round the entry and exit ports of the diaphragm meters to make the clock go backwards will have no effect on the electronic meters, because they measure gas going in either direction. This will also increase safety: making the meter clock go backwards can cause an explosion.

Siemens has spent more than six years developing the meter, after a competition organised by British Gas in 1987 in which more than 20 companies submitted designs for meters that could be read remotely.

Another company, Gill Electronic of Lymington, Hampshire, also had its design accepted. It is still awaiting approval of its meter from the Department of Trade and Industry (Siemens received DTI approval in November 1993) but it has set up a company called Eurometers to make the devices.

At first the electronic meters will be read in the time- honoured fashion. British Gas is still experimenting with remote reading of meters. It is running a trial in North London in which a thousand conventional meters have been adapted to transmit readings by radio to the billing computer.

The ability to read meters remotely, and frequently, will smooth the path of liberalising the domestic gas market from 1998, when a variety of gas companies will be able to supply gas using the British Gas infrastructure. How the liberalised gas market will operate is yet to be decided, but it will be necessary to read meters more frequently than every three months, so that suppliers can monitor how much gas their customers are using and put the right amount into the system.

The electronic meter could also make it possible for consumers to switch between suppliers, allowing them, for example, to take advantage of cheaper tarriffs at different times of the day, because it can record when gas is used. (Photograph omitted)