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Resisting underwater attacks

24 August 2015

Who would have thought the humble resistor would play such an important role in keeping our waters safe?

One company is doing just that - the metal oxide resistors they buy from Rapid are used in products being employed in the frontline of anti-submarine warfare (ASW) operations. The airborne sonar devices detect sound waves from other sub-aqua bodies. They are housed in canisters and dropped into the sea from the air, using balloons. Once underwater the canisters open and the receiver is deployed. The only clue to the presence of the device is a traditional buoy which floats on the surface.

metal oxide resistor

The company - which has asked that it remain anonymous because of the sensitive nature of its work - supply three different kinds of device: passive, active and bathythermal. The passive devices do not emit a wave but check for acoustic signals from other bodies; the active version emits sound waves into the water and listens for a returning echo; the bathythermal device relays changes in water temperature up to depths of 800 metres to the operator.

Each device has a limited lifespan once activated, ranging from 12 minutes to 8 hours. This is where the resistor comes in: it is designed to overcharge itself, so when the device has completed its task, the resistor burns itself out, deflating the surface buoy. Metal oxide resistors are ideal for this application because of their high endurance properties and high temperature coefficient. Their power rating, voltage ratings and overload capabilities exceed the performance of metal film and carbon film resistors.


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