In the parameters of flow meters, what does F.S. mean in the measurement error of 0.5 %F.S.?

You’re right; it does mean full scale, that is, the maximum range.

When measuring the fluid flow rate in a pipe, it is often necessary to understand its flow state, velocity distribution, etc. The Reynolds number is an important parameter that characterizes the flow properties of a fluid. The ratio of the inertial force Fg to the viscous force (internal friction force) Fm during fluid flow is called the Reynolds number. It is denoted by the symbol Re. Re is a dimensionless quantity. A low Reynolds number means that the viscous forces between the fluid particles play a dominant role during flow; the particles move in an orderly manner parallel to the inner wall of the pipe, resulting in laminar flow. A high Reynolds number means that inertial forces play a dominant role, and the flow is turbulent. Generally, in pipes, a Reynolds number Re < 2000 indicates laminar flow, Re > 4000 indicates turbulent flow, while Re = 2000–4000 represents a transitional state. Under different flow conditions, the laws governing the motion of the fluid and the distribution of flow velocities vary; as a result, the ratio of the average flow velocity υ of the fluid in the pipe to its maximum flow velocity υmax also differs. Therefore, the value of the Reynolds number determines the flow characteristics of viscous fluids. When using flow meters with throttling devices, the minimum Reynolds number comes into play.

When measuring the fluid flow rate in a pipe, it is often necessary to understand its flow state, velocity distribution, etc. The Reynolds number is an important parameter that characterizes the flow properties of a fluid. The ratio of the inertial force Fg to the viscous force (internal friction force) Fm during fluid flow is called the Reynolds number. It is denoted by the symbol Re. Re is a dimensionless quantity. In the formula, the dynamic viscosity η is replaced by the kinematic viscosity υ, since η = ρυ. Therefore, in the formula: l υ – the average velocity of the fluid ； l l——Fixed dimensions of the beam ； l ρ, η – in operating condition ； Kinematic viscosity and dynamic viscosity of the fluid: μ = ρ – density of the fluid under examination ； As can be seen from the above equation, the value of the Reynolds number Re depends on three parameters, namely the velocity of the fluid, the characteristic size of the flow stream, and the viscosity under operating conditions. When transporting fluid through circular pipes and calculating the Reynolds number, the characteristic dimension is generally taken as the pipe diameter (D). When transporting fluid through square pipes, the characteristic dimension is the equivalent diameter (Dd). The equivalent diameter is equal to four times the hydraulic radius. For a pipe of any cross-sectional shape, its hydraulic radius is equal to the ratio of the area of the cross-section to its perimeter. Therefore, for a rectangular pipe with lengths A and B respectively, its equivalent diameter can be calculated as the ratio of four times the cross-sectional area to the perimeter of the cross-section. The equivalent diameter of a pipe with any cross-sectional shape can be determined in the same manner, by using the ratio of four times the cross-sectional area to its perimeter. A low Reynolds number means that the viscous forces between the fluid particles play a dominant role during flow; the particles move in an orderly manner parallel to the inner wall of the pipe, resulting in laminar flow. A high Reynolds number means that inertial forces play a dominant role, and the flow is turbulent. Generally, in pipes, a Reynolds number Re < 2000 indicates laminar flow, Re > 4000 indicates turbulent flow, while Re = 2000–4000 represents a transitional state. Under different flow conditions, the laws governing the motion of the fluid and the distribution of flow velocities vary; as a result, the ratio of the average flow velocity υ of the fluid in the pipe to its maximum flow velocity υmax also differs. Therefore, the value of the Reynolds number determines the flow characteristics of viscous fluids. The relationship between the pipe Reynolds number Rep of a smooth pipe and the velocity ratio V/Vmax shows that, when the external conditions are geometrically similar (geometrically similar pipes, fluid flowing through geometrically similar objects, etc.), if their Reynolds numbers are equal, then the flow state of the fluid is also geometrically similar (hydrodynamic similarity). This similar principle is precisely the basis for the standardization of throttling devices used in flow measurement. It can be seen that the Reynolds number, which accurately reflects the flow characteristics of a fluid, is a commonly used parameter in flow rate measurement. The formula for the Reynolds number in terms of flow rate is as follows: M – the mass flow rate of the fluid being measured, in kg/h; Q – the volumetric flow rate of the fluid being measured, in m/h ； D——Inner diameter of pipeline in mm ； v – The dynamic viscosity of the medium under operating conditions, in Pa·S; p – The kinematic viscosity of the medium under operating conditions, in m2/s. The constant values in the formula vary depending on the units of the various parameters used in it. When units other than those specified in the formula are used, the constant values shall be adjusted accordingly. When using the Reynolds number, attention should be paid to the corresponding characteristic size. Generally, a superscript is indicated in the lower right corner of the given Reynolds number Re to indicate the corresponding dimensional size. In the standards for throttling devices, the Reynolds number relative to the pipe diameter D is denoted as ReD, while the Reynolds number relative to the orifice diameter d of the throttling element is denoted as Red. The relationship between the two is ReD = βRed, where β is the diameter ratio of the throttling element, that is, β = d/D; this factor must be taken into account when using such standards. 2. Reynolds number: Experiments show that what truly determines the flow pattern of a liquid is a dimensionless number called the Reynolds number Re, which is determined by three values: the average flow velocity v inside the pipe, the dynamic viscosity ν of the liquid, and the pipe diameter d. The critical Reynolds numbers are as follows: When the Reynolds number corresponding to the actual flow of the liquid is less than the critical Reynolds number, the flow is laminar; otherwise, it is turbulent. The critical Reynolds number for common fluid flow pipes can be determined experimentally. Physical meaning of the Reynolds number: The forces that affect fluid flow are primarily inertial force and viscous force, and the Reynolds number is the dimensionless ratio of inertial force to viscous force. For pipes with non-circular cross-sections, Re can be calculated using the following formula: Re = 4vR/ν, where R is the hydraulic radius of the flow cross-section. It is equal to the ratio of the effective cross-sectional area A of the fluid flow to its wet perimeter χ (the perimeter of the solid wall surface in contact with the liquid at the flow cross-section), that is, R = A/χ. The hydraulic radius has a significant impact on the flow capacity of a pipe; a larger hydraulic radius indicates less contact between the fluid flow and the pipe walls, resulting in a higher flow capacity ； A small hydraulic radius indicates more contact between the fluid flow and the pipe wall, resulting in a low flow capacity