The range ratio of a metal tube float flowmeter refers to the ratio of its maximum measured flow rate to its minimum measured flow rate, which is influenced by various factors such as the shape and structure of the float, the characteristics of the measuring tube, fluid properties, and instrument accuracy. The following is a specific introduction:
Float factor
Float shape: Floats of different shapes have a significant impact on the range ratio. For example, spherical floats experience relatively less resistance in fluids and can respond more sensitively at low flow rates, but their stability may be slightly poorer at high flow rates; Cone shaped floats have better stability at high flow rates and can withstand greater fluid impact forces, but their sensitivity may not be as good as spherical floats at low flow rates.
Float mass and density: The mass and density of a float determine the magnitude of its gravity and buoyancy in the fluid, which in turn affects the range ratio. Floats with lighter weight and lower density are more easily pushed up by the fluid at low flow rates, which can reduce the minimum measured flow rate of the flowmeter and expand the lower limit of the range ratio; But at high flow rates, the stability may deteriorate due to the lightweight of the float, affecting the upper limit of the range ratio.
Float structure design: The internal structure design of the float will also affect the range ratio. If the float is equipped with stabilizing wings or flow guiding devices, it can maintain better stability and linear motion in the fluid, reduce the influence of fluid eddies and turbulence on the float, and enable the flowmeter to accurately measure over a wide flow range, effectively improving the range ratio.
Measurement tube factor
Measuring tube taper: The taper of the measuring tube is one of the important factors affecting the range ratio. A larger taper will make the relationship between the displacement of the float in the measuring tube and the change in flow rate more sensitive. Under the same flow rate change, the displacement of the float will be greater, which is beneficial for expanding the lower limit of the range ratio; However, excessive taper may cause instability of the float at high flow rates, affecting the upper limit of the range ratio.
Measuring the roughness of the inner wall of the measuring tube: The roughness of the inner wall of the measuring tube will affect the frictional force between the fluid and the float, as well as the flow state of the fluid. Excessive roughness of the inner wall will increase the frictional force of the fluid, making it difficult for the float to move at low flow rates, resulting in an increase in the minimum measured flow rate and a decrease in the range ratio; Meanwhile, rough inner walls may also cause turbulence in the fluid, affecting measurement accuracy and stability, further limiting the range ratio.
Fluid factors
Fluid viscosity: Fluids with higher viscosity have greater resistance to the float, making it difficult for the float to move at low flow rates, resulting in an increase in the minimum measured flow rate of the flowmeter and a decrease in the range ratio. For example, when measuring heavy oil or high viscosity chemical raw materials, due to the viscosity of the fluid, the range ratio of the metal tube float flowmeter may be smaller than when measuring water or low viscosity fluids.
Fluid density: Changes in fluid density can affect the buoyancy of the float, which in turn affects the measurement range of the flowmeter. When the fluid density increases, the buoyancy of the float increases, and the position of the float will relatively rise at the same flow rate, which may change the measurement range of the flowmeter and have a certain impact on the range ratio.
Fluid temperature and pressure: Changes in temperature and pressure can cause physical properties such as volume and viscosity of the fluid to change, thereby affecting the measurement accuracy and range ratio of the flowmeter. For example, under high temperature and high pressure, the volume expansion and viscosity decrease of the fluid may reduce the minimum measured flow rate of the flowmeter and expand the range ratio; But if the temperature and pressure changes too much, exceeding the design range of the flowmeter, it may also lead to an increase in measurement error and affect the range ratio.
Instrument intrinsic factors
Instrument accuracy requirements: High precision metal tube float flowmeters usually require a narrow flow range to ensure measurement accuracy, so their range ratio is relatively small; For situations with lower precision requirements, flow meters can measure over a wider flow range, with a relatively larger range ratio.
Signal conversion and processing capability: Advanced signal conversion and processing technology can improve the sensitivity of flow meters to detect small displacements of floats, thereby expanding the lower limit of the range ratio. For example, using advanced detection components such as high-precision Hall sensors or capacitive sensors can more accurately measure the position changes of the float, achieve accurate measurement of low flow rates, and improve the range ratio.
