Current meter performance with CF2 controller

Testing and calibrating a current meter is part of bringing a new design into production. The opportunity to demonstrate this has been provided by the re-engining of the acoustic differential travel-time current meter, MAVS (Modular Acoustic Velocity Sensor) [1]. In 2012, the supplier of the controller used by MAVS announced End of Life for their product. A search for a suitable replacement took a year, and in summer 2013, the CF2 by Persistor [2] was selected. The interface board to adapt the CF2 to the footprint of its predecessor on the MAVS mother board was designed in midsummer 2013 and laid out in the fall of 2013. Circuit boards were etched in late fall of 2013 and the first prototype was tested in January 2014. A significant trial of the interface board was to adapt the 3.3v CF2 to the 5v logic of MAVS with minimum impact on the well-tested and validated MAVS. This required level shifter circuits for both up shifting and down shifting on the interface board. These were tested without the new code required to run the program of measurement. Power switching imposes another constraint since it is necessary to turn off the 5v logic between measurement bursts while the 3.3v CF2 is still running. An up shifter circuit requires that the output never be lower voltage than the input but without the 5v logic powered there is an issue, solved for now by a voltage limiting Schottky diode to protect the up shifter when powered down. The consequences on the powered down 5v logic have yet to be tested.