Sonar Recording

In the mid 1980’s Avalon Electronics secured a contract with the UK MOD to provide Sonar Data Recorders to the Royal Navy. These were designed to provide an operational life of 1,000 hours, before servicing would be required.

The Navy were closely monitoring their existing Instrumentation Recording systems, because when they went wrong, they overwrote the Sonar operating system.

The Captain then had to retrieve the “Punched Tape” from the top secret safe and reinstall the Sonars operating system, clearly a major failure.

To ensure this could not happen with Avalon Recorders, a powerful Error Detection and Correction processor was developed. The power of the error correction could be demonstrated by removing a 3 mm square of oxide from a recorded tape, and then replay the previously recorded data, error free.

VHS recording tape is specified to work at “Room Temperatures” with 25 deg C specified as the maximum. Some of the recordings made when the trials of the recorders were taking place would not replay, and Avalon were asked to investigate. It was discovered that at room temperatures the diameter of the Aluminium Drum, which held the rotating heads, was now too small to replay the signals correctly.

In order to enlarge the Drum to the same size diameter it reached when the recording was made, an “Infra Red Lamp Heater” was used to apply local heat to the drum.

The drum had to be heated to 40 deg C to recover the recorded data. This showed that despise being designed for the domestic environment, the VHS technology could cope with temperature ranges much in excess of its published 25 deg C maximum. Clearly VHS Tapes and Mechanisms, were far more robust that the manufacturers would sign up to.

As the first systems were about to be deployed for the acceptance trial, Avalon became aware that the Main Contractor to the MOD, through whom the recorders were purchased, intended to purchase low cost tapes from any source. This would have been a recipe for disaster.

To circumvent this, Avalon “Nato Codified” one grade of tape from one manufacturer, and insisted that only this tape be used. This proved to be vital for reliability and longevity of service.

Because of the unreliability of the previous systems, the reliability of the new one was monitored each month and a report sent.
The reliability proved to be so good that the message we received after the first six months of deployment was that, “Provided the operator pushes the “Record Button” we always get the data. Sometimes they select Play Button in error”

One of these Navy systems was found to have recorded tape after tape, for over 21,000 hours without error, before somebody realised that it should have been serviced 20,000 hours previously.

A group of 50 Royal Navy recorders were monitored over a period of time, and achieved over 1,000,000 operational hours without a single reported failure.

Some Avalon recorders were still in front line service 25 years after their first deployment.