Dynasonics DT9 [DT94-100-A-100-N] Doppler Ultrasonic Transducer Set, Standard Temperature & Standard Pipe, 100 Feet (30m) Cable Length, 100 Feet (30m) Flexible Armored . The DT9 series transducers are non-invasive, clamp-on devices that are placed on the outside of a pipe. Proprietary circuitry allows this product to be used on both metal and plastic pipes containing relatively clean liquids as well as those with suspended solids or entrained gases. Series DT9 clamp-on, transducers are recommended for use on most pipes constructed from metal or plastic. The Dynasonics DT9 can be located up to 990 feet (300 meters) from the DFX display enclosure utilizing RG59 coaxial cable. Operating Principle: Each transducer utilizes a piezoelectric crystal to transmit ultrasound through a pipe wall and into a flowing liquid. The ultrasonic signal is reflected from suspended solids or entrained gases drawn out of solution by hydraulic disturbances such as a 90° elbow. (This unit can measure the flow rate of clean liquids by mounting the transducers 1 to 3 pipe diameters downstream of the 90° elbow.) A second transducer receives the reflected sound and the DFX series meter's circuitry compares the transmitted and received frequencies. If the liquid is moving, a frequency (phase/Doppler) shift occurs which is proportional to fluid velocity.