Considerations for selecting flow meters

Thread Content

I. Fluid under test 　　In terms of the fluid under test, there are three types of fluids with different physical properties: gases, liquids, and mixed fluids. In terms of the conditions of the fluid under test: from high temperature to low temperature, from high pressure to low pressure, and from low flow rate to high flow rate. Furthermore, in the case of liquids, there are also differences in viscosity levels. Due to the complex properties of the fluid under measurement and the varying measurement conditions, various measurement methods and instruments have been developed. Therefore, when selecting instruments, the first step is to choose the measurement method, and the second step is to select the instrument model. II. Bore: The nominal diameter of the pipe connected to the instrument body. III. Flow range, range ratio, and scale The flow range refers to the interval defined by the maximum flow rate and the minimum flow rate. Range ratio, the ratio of the maximum flow rate to the minimum flow rate. Range: the algebraic difference between the upper limit and the lower limit of the flow rate range. IV. Precision and Error Allowable error and accuracy levels. The maximum error of a flow meter under specified normal operating conditions is known as the allowable error of that flow meter. The accuracy levels generally include 0.02, 0.05, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, and 4.0. V. Temperature range: The temperature requirements imposed by the instrument on both the application environment and the medium being measured. VI. Humidity range: The requirements of the instrument regarding the humidity of the operating environment. VII. Connection method: The way in which the instrument is connected to the pipeline containing the medium to be measured, including flanges, flange clamping, clamps, threads, etc. VIII. Response Time The time it takes for the output variable to begin changing as a result of an input variable. The shorter the response time, the faster the signal transmission; the longer the response time, the slower the signal transmission. IX. Pressure Loss The pressure loss of a flow meter refers to the irreversible pressure decrease that occurs as fluid flows through the flow meter. Atmospheric pressure is the static pressure generated by the weight of the air. The atmospheric pressure at sea level at 0°C is often used as a standard, with a value of 0.1013 MPa. Absolute pressure is the actual pressure exerted on an object. Relative pressure is the difference between absolute pressure and the atmospheric pressure at that location and time. Gauge pressure is the relative pressure when absolute pressure is greater than atmospheric pressure; it is the difference between absolute pressure and atmospheric pressure. Vacuum level (negative pressure) is the relative pressure when the absolute pressure is lower than atmospheric pressure. That is, the difference between absolute pressure and atmospheric pressure. Since the absolute pressure is lower than atmospheric pressure, the difference is negative; hence it is also referred to as negative pressure. X. Output Signal: Analog output types of 0–10mA, 4–20mA, and 1–5V; pulse frequency output type; and analog pulse-compatible output type (leveraging the CPU’s powerful computing capabilities). XI. Load refers to certain electrical parameters that must not be exceeded when the instrument is in operation. 12. Repeatability refers to the degree of inconsistency in the readings obtained when the same quantity being measured is tested multiple times under identical working conditions. Repeatability indicates the magnitude of the random error of the instrument. 13. Stability refers to the ability of a flow meter’s certain performance characteristics to remain constant over time under specified operating conditions.