Influence of the variable geometry of the flow switch nozzle exit on the metrological characteristics of a calibration unit with weighing devices

This article discusses the issues regarding the improvement of the metrological characteristics, weight, dimensions, and technical and economic indicators of calibration units with weighing devices because of the introduction of a flow switch with variable nozzle exit geometry to their design. The use of this flow switch design can solve the problem of filling the nozzle exit with water, reduce the dimensions of the hydraulic path, simplify the maintenance procedure, and minimize the cost of installation. This work describes the design, operating principle, and timing diagram of a flow switch with variable nozzle exit geometry. Herein, the local hydrodynamic characteristics of water flow were investigated using a Pitot tube with changes in the nozzle exit width and mass flow rate in the range of 25–550 t/h. Moreover, the optimal values of the nozzle exit width were experimentally determined based on the value of the liquid mass flow rate, at which it is filled with water. Using a comparison standard, the metrological characteristics of a calibration unit with weighing devices, which include a flow switch with variable nozzle exit geometry, were analyzed in a wide range of liquid mass flow rates. Additionally, the impact of the nozzle exit width on the metrological characteristics of a calibration unit with weighing devices in the investigated range of liquid flow was established. Dependency diagrams of the expanded measurement uncertainty of the installation when reproducing the unit of liquid mass flow rate on the measurement time interval and the liquid mass flow rate are demonstrated here. From the results, the optimal values of the nozzle exit width and measurement time intervals were determined based on the liquid mass flow rates when using a flow switch with variable nozzle exit geometry. Furthermore, the operation range expansion of weighing devices, which are part of the calibration units with weighing devices, is justified. The proposed design of the flow switch with variable nozzle exit geometry is recommended for use in the design and modernization of operated calibration units with weighing devices of flow switches.