Telephone lines provide global warnings

Remote weather stations are downloading data providing tidal predictions, storm and flood warnings via robust industrial grade modems and 'line power', as Dr Geoff Lawlor of Jekyll Electronic Technology explains.

The Proudman Oceanographic Laboratory (POL) is a leading world centre in sea level measurement, tidal prediction and storm surge forecasting. It hosts the UK’s Ministry of Agriculture Fisheries and Food(MAFF)-funded Tide Gauge Inspectorate, which has developed and maintained the National Tide Gauge Network. There are 44 operational sea level stations on this network around the UK coastline, each connected to POL and the Meteorological Office as part of the country’s Storm Tide Forecasting Service.

World-wide observations

POL has also developed and operates an international network of stations as part of the Global Sea Level Observing System (GLOSS). The data are used for studies of long term Climatic Change and the associated world-wide rise in sea level. The stations are on the islands of Ascension, St. Helena, Tristan da Cunha, the Falklands and at the British Antarctic Survey bases in the South Polar Region. Like the UK Tide Gauge Network, most of the stations return their data via the telephone network, although Antarctica’s is via satellite.

Accurate advance flood warnings depend on rapid access to recorded data from weather stations quickly. But what happens when conditions are so harsh that mains power lines go down and weather stations are located hundreds, even thousands, of miles away?

One answer is to unite modem technology with the on-site environmental monitoring equipment to transfer the data over a secure telephone line. Line powered modems offer the facility to operate during mains power supply failures.

For successful remote monitoring, it is vital that modems are built to exacting standards using robust components to minimise communication errors and reduce the possibility of failure. This is particularly important for transferring data from weather stations that are located in remote areas and subject to adverse and hazardous conditions.

In an ideal situation, an operator simply dials up the modem from a centralised terminal, downloads the gauge measurements into a spreadsheet, disconnects the modem from the telephone line, then proceeds with the necessary data analysis.

Whilst most modems arrive with default factory settings, it may be necessary to adjust the internal commands to ensure an optimal communication. Different configurations may be set; whether for manual operation, periodic interrogation, or only making a connection when the measured data exceeds some pre-defined limits. Warnings can then be issued by the authorities at the appropriate time to the general public or to other interested users.

Low power telemetry

POL has selected a low power telephone telemetry system from Jekyll Electronic Technology which can customise packages for individual applications such as remote utility meter reading and diagnostics, as well as remote weather stations. Such modems have been useful in the water industry where mains power installations are hazardous. They are now finding applications in the scientific community.

POL uses a variety of industrial grade modems from Jekyll, including the Telemodem2 Freedom, Telemodem/32 and Jet/22 ranges. The Telemodem2 is ideal for frequent connections with a connection speed up to 2400 bps.

A robust construction provides operational stability over a wide temperature range, allowing it to work in demanding environments. The UK’s Meteorological Office periodically relies on such units to effectively transfer data, such as average tidal height levels. POL on the other hand dials up the units to make more detailed enquiries for research.

One of the main benefits of Jekyll’s modems is ‘line power’. Rather than using mains power, the modems draw all their power from the telephone line. This means the units operate during mains power cuts, giving users access to vital wave data whenever required.

The modem also features PHANTOM, or Caller Line Identity, technology which enables the unit to share existing telephone lines primarily used for voice or fax traffic. It is also possible for Jekyll to monitor the Telemodem2 from the manufacturing premises for convenient remote diagnostic servicing.

Remote station status

For its South Atlantic network, POL uses Jekyll’s Tel/32 modem technology which features a 14,400 bps connection speed to transmit large volumes of data.

‘Visiting the Islands individually is a lengthy and often hazardous process, but Jekyll’s modems allow us to have complete control over the status of our sea level stations around the world,’ says Peter Foden from POL. He added, ‘The stations are located at remote sites and operate for long periods of time, so the gauges and modems have to be reliable and rugged.’

The gauges feature a Persister CFI microprocessor board, so in effect they are versatile computers in weather robust housings. The data ports on the modem can be quickly assigned for data communication, and Jekyll increased the ‘time-out’ settings to 2 minutes, so the modem does not automatically disconnect before all the data is transferred.

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