Environmental monitoring goes underground

Meaco have been manufacturing and installing radio telemetry systems since 1993 when the very first wireless system for collecting data on temperature and humidity in museums was supplied to the V & A. Since then hundreds of radio systems have been installed right across the UK and Europe in museums, stately homes, libraries and archives.

Every site has it own unique challenges for radio technology. Under ideal conditions radio signals can travel for miles. Put a few obstacles in the way and the distance radio travels starts to reduce. If you happen to be in a castle with three metre thick stone walls radio transmissions can be seriously impaired!

So when Meaco was approached by English Heritage to install a wireless monitoring system in the Secret Wartime Tunnels at Dover Castle the project turned out not only to be one of the most interesting jobs, but also one of the most challenging.

The tunnels were dug during the Napoleonic Wars about fifteen metres below the cliff top, to house at its peak more than 2000 soldiers. During WWII the tunnels were converted into an underground hospital, telephone exchange and command centre and it was from here that the evacuation of Dunkirk was co-ordinated.

The remit of the project was for English Heritage to be able to monitor and record the environmental conditions within the tunnel complex and to be able to view this data from their London office.

The biggest challenge to the project was to devise a method of getting the radio data out of the tunnels back to a networked PC. Radio signals do not travel very far underground let alone through fifteen metres of chalk and soil. Fortunately, running through the tunnels was a ‘leaky feeder’ cable. A leaky feeder is a communications system used in underground mining and other tunnel environments to allow two way radio communications. The plan was to use the leaky feeder system to piggy back the radio data back along the tunnels to a point where the information could be transmitted back to the networked computer without interfering with normal radio operations.

Additional challenges included monitoring in locations where the cable didn’t run. The sensors were placed on an extension leads allowing the transmitter to stay within range of the leaky feeder and the sensor to be placed where the monitoring was required – up to one hundred meters away.

The environmental conditions of the site also had to be taken into consideration and the effect they could have on the equipment. The high humidity levels and salt content in the air would seriously compromise less reliable sensors so the decision was made to use industrial enclosures in conjunction with HygroClip sensor that offers an accuracy of +/-1%rh from 0 to 100%. The sensors themselves were fitted with Teflon filters to prevent any contamination getting onto the sensor filament to ensure accurate and reliable readings despite the difficult conditions.

Once the radio data reached the surface it was relayed back to the monitoring PC where the information could be viewed on the Sensia monitoring software. Sensia can be viewed via networks or the internet and this made remote access to the data from the London office very straight forward.

The end result is a wireless environmental monitoring system across three levels of the tunnel complex providing real-time data that can be viewed across the English Heritage network and enable the dedicated members of staff react proactively to adverse conditions within the site. It also shows that whatever type of building or monitoring application you may have Meaco have the tools, experience and flexibility to overcome the hardest challenges.