The contemporary rating carriage was made by the DICONT a.s., a small Czech joint-stock company, and put into regular operation in January 2005. The carriage has electric propulsion, the power is fed by a trailing wire track system of the tank and the carriage moves on a rail track which is laid along the working section of the tank. The carriage controlling unit enables to choose arbitrary speed of the carriage movement in an interval of 0.02 to 10 m/s (the maximum speed is currently limited to 7 m/s) at both directions. The carriage has three holders for calibration of current meters suspended on rods and a winch for calibration of current meters suspended on rope with sinker weights up to 100 kg. The holders automatically turn the meters around when the direction of the carriage movement is changed. The carriage can be operated either manually from the carriage console or remotely from the control room. It is possible to input all parameters of the fully automated operation from the control room. The fully automated operation is used only for rod suspended calibration, in case of cable suspended calibration there must be an operator on the carriage. The control computer is an industrial computer of the PC class and carriage movement control is based on a custom program which was supplied by the DICONT a.s. together with the carriage.
After uniform movement of the carriage is reached, the control computer starts a data acquisition. The first impulse from every meter switches the appropriate distance, time and impulse counters on. When the predetermined impulse count from the meter is reached, the counters are switched off and the data are sent to the central computer for a consecutive processing. The time is derived from the computer crystal oscillator. The distance is determined from the number of impulses caused by optical-electronic system moving along the distance gauge – a metal strip with slits at mutual distance of 0.10 m. In between the slits, the distance is interpolated on a basis of optoelectronic sensing of angular division of shafts of the driving electric motors. Measurements of the distance and the time are metrologically traced to the main standards of accredited laboratories. Acquired data are transmitted from control unit of the carriage to central computer in the control room and then processed by calibration evaluation program.
The rating carriage can be used not only for current meters calibrations, but also for experiments with towing bodies in still water, e.g. for determination of hydrodynamic resistances of ship hulls etc.
