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Today ultrasonic impulses are employed to measure depth. The impulses are known as ultra sound as they lie outside the range of normal human hearing. We humans generally have very poor hearing in comparison with some other denizens of the planet and our hearing is restricted to around 2 kHz. This is a lower frequency than any that are currently used in echo sounding. Depending on temperature, sound travels at 1500 m/s under water. This can be accurately and easily measured and recorded graphically on the screen of an echo sounder. Essentially, an echo sounder is a device that transmits and receives sound, accurately measuring the time it takes to leave the sounder, reach the bottom and return to the sounder. It then converts this information into digital or graphic representations of the bottom depth and relief.


The average echo sounder consists of a transmission and reception unit that sends sound signals through the water, receives and decodes information and converts that information into either a graphic or visual form. Attached to the receiver is a transducer that acts as a microphone and a speaker under the water. Sound waves travel at approximately 1500 m/s through the water dependent on water temperature.


The receiver unit measures the time taken for one pulse of sound to travel to the bottom or an intermediate object and return to the sounder. From this measurement the echo sounder produces graphic or digital information that represents the depth of water and the position of mid water objects relative to the bottom. Transducers are mounted in a variety of ways depending on the hull and propeller configuration of the boat. Transducer construction depends on the type of frequency and power of the sounder they are being driven by. In a way, transducers have a fair bit in common with speakers in the domestic stereo systems.


Transducers which are required to transmit high power, low frequency sound are usually large and metallic in construction, while those which transmit low power, high frequency sound are usually made from ceramics and are much smaller


LMS is also associated in the sales and services of the latest available technology in Tide gauges which are used for measuring depth.


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               Last modified: 07/26/05