The Remote Stations.

Brown Clee Seismic Station.

The remote station is based on a 'WillmoreMK3' seismometer donated by the BGS. This is housed in a piece of soil pipe approximately 1 metre long by 20 cm wide and buried vertically beneath the ground. In the same tube is an amplifier/modulator this amplifies the tiny seismic signals from the seismometer and converts them into an audible tone to be transmitted over VHF radio. The tone is constant 676Hz if the seismometer is perfectly still. In the event of seismic activity the tone would deviate by as much as 40%. Some 25 metres away from this buried apparatus is a transmitter and solar/battery power supply.

This station has been in operation for several years and is very reliable. The only fault was water ingress in the coax cable. A tiny split was found this resulted in having to replace the entire length of coax, all 7 meters of it !.

The Brown Clee station has since been duplicated and installed at 'Spaceguard' Knighton Powys. This seismic station was installed in March 2003 and is in a quiet environment so false alarms are very rare. There have been no problems with this station apart from a transmitter failure caused by a single electronic component. The apparatus is solar powered but consumes rather more power than the Brown Clee station due to a weather station (RAWS) running on the same battery bank. During the winter months a wind generator is temporarily installed at the site to supply additional power as solar energy becomes insufficient to power the station.

 

 

Here we can see the seismometer and amplifier/FM modulator. These units are installed in a piece of 200mm diameter soil pipe which is buried vertically beneath the ground. The seismometer sits at the bottom of the pipe on a bed of concrete at approximately 1 metre below surface level the amplifier/modulator sits nearer the top of the pipe where the FM signal is wired out to the transmitter some 20 metre's away.

Below is the picture of the underground container for the transmitter. (Now replaced with larger capacity container August 2009)

The 500 mW 458MHz transmitter is shown above .

In August 2009 Woodbank underwent a station upgrade involving replacing the transmitter and transmitter vault. During this operation routine maintainance was also carried out on the seismometer pit. The image below is of the area in which the seismometer is installed and right is the tube housing the seismometer and amplifier.

 

To the left we can see the tube cover has been removed along with the amplifier revealing the seismometer one metre below the earths surface.

The seismometer tube hole was excavated in about 30 minutes using an ordinary garden spade, soiltype is a light and slightly sandy which made work easier. Once the one metre depth was reached a small amount of concrete was poured into the hole and the tube placed in situ, the hole was then back-filled ensuring the walls were vertical and the concrete base tamped to an nice level finish. The concrete was allowed to set for a day before the sensor was installed along with the amplifier, a small hole was drilled into the tube wall to allow cable entry and resealed with silicon sealant. Finally the cover was attached to the tube and after testing the the installation it was covered and the turf replaced.

 

 

 

For details on the Spaceguard station click here .