Profile: Radarsonics, Inc. manufactures transducers. We provide sonar transducers, switch boxes, sensors and accessory items. All multifunction transducers use the same components to determine speed. A magnetic paddlewheel passing by a hall effect switching device produces 3 pulses per revolution or 22,500 pulses per nautical mile. Speed range is .5 knots to 50 knots (40 knots on thru-hull models). Its linearity is plus/minus 3 percent over speed range. The 408 models of speed/temperature sensors feature removable modules to allow cleaning and inspection of the paddlewheel. A blank plug is provided to insert into the hull fitting during this operation. The module and plug have dual O-ring seals, and are secured into the hull fitting with a stainless steel pin & ring. An extra safety feature on model 408P is a length of stainless steel chain to hold the module in place should it receive a blow from the outside.