Author(s): Joachim Lengricht; Gerd Stephan; Wolfgang Frey
Linked Author(s): Joachim Lengricht
Keywords: Discharge measurement; Acoustic transit time flowmeter; Monitoring of Venice lagoon
Abstract: 18 networked discharge measurement stations are installed around the Venice lagoon to monitor both the drainage into the lagoon and the interaction between the lagoon and the open sea by a continuous discharge measurement. The acoustic measurement paths have a range of lengths from 10 to 564 m but all of the stations were equipped with traditional cable connected flowmeters. At the moment they are updated step by step with brand new ultrasonic transit time flowmeters synchronized wirelessly by GPS and Bluetooth. A new acoustic transit time flowmeter system is introduced here combining the advantages of substituting underwater cables and maximum profiling ranges up to 2000 m. The underwater cables are substituted by a self-sustaining, synchronously working wireless system containing transmitter and receiver on both watersides. A novel measurement concept was developed to design self-governed transmitter and receiver units clocked and synchronized by a GPS-signal and pair wise adjusted in the Nanosecond range. The imperative of a nearly absolute synchronization for every pulsed cycle could be reached by a master and slave solution. The master on the one waterside and the slave on the opposite side communicate using a synchronous transmission digitally controlled by a GPSboard. The board converts the externally triggered GPS-pulse into a periodic synchronization using a GPS-protocol. The communication between master and slave is realized either by directive arrays, a Wireless Local Area Network (WLAN) or Bluetooth (BT). The loop control between master and slave could be achieved by a pure software solution, i. e. any interference caused by the hardware itself can be eliminated. The control word sent by the master is replied by the status message and the metered value by the slave in this software controlled circuit. The transit time difference determined and sent by the slave is analyzed and converted to the value for the discharge by the master finally.
Year: 2007