What is a mass flow meter?

Principles and Applications of Mass Flow Meters I. Basic Concepts of Mass Flow Meters II. Development of Mass Flow Measurement Technologies III. Typical Structure and Working Principle of Coriolis Mass Flow Meters IV. Applications of Coriolis Mass Flow Meters Principles and Applications of Mass Flow Meters ——Basic Concepts of Mass Flow Meters (1) Definition of the Instrument (2) Classification of Instruments (3) Measurement Characteristics of Instruments (4) Uncertainty in Instrument Measurements Basic Concepts of Mass Flow Meters ——Definition of the Instrument A mass flow meter is an instrument that continuously measures the flow rate of the medium being measured, with the measurement results displayed in engineering units such as kilograms or tons. Basic concepts of mass flow meters – Instrument classification. A mass flow meter is a type of inferred flow meter, and it can be divided into two main categories based on the measurement method: one is indirect measurement of mass flow, which involves measuring both the volumetric flow rate and density of the fluid; the mass of the fluid is then calculated using an operational amplifier. The other method involves measuring both the volumetric flow rate and the temperature and pressure of the fluid, and the mass of the fluid is determined by utilizing the relationship between fluid density and temperature and pressure ； The second is the direct mass flow measurement method, in which the fluid measurement directly reflects the mass flow value, independent of changes in parameters such as the fluid’s temperature, pressure, and density. Basic concepts of mass flow meters – Instrument classification 1. Indirect mass flow meters (1) Differential pressure flow meters with pressure and temperature compensation (2) Volume flow meters with pressure and temperature compensation 2. Direct mass flow meters (1) Thermal mass flow meters (TMF): a. Thomas flow meter b. Boundary layer flow meter c. Bypass tube flow meter (2) Impulse-type mass flow meters (impingement plate type) (3) Differential pressure mass flow meters (orifice plate + constant flow pump) (4) Twin-turbine mass flow meters (5) Coriolis mass flow meters Basic concepts of mass flow meters – Measurement characteristics of instruments The measurement characteristics of instruments (static and dynamic characteristics) Static characteristics: Refer to the relationship between input and output when the value being measured is in a stable state. The basic requirements for static characteristics are: the output is zero when the input is zero, and there is a one-to-one correspondence between the output and the input. Parameters that characterize static properties include: static transformation function, static characteristic curve, meter coefficient, discharge coefficient, flow range (scale), linearity, sensitivity, hysteresis, stability, zero drift, repeatability, accuracy, and pressure loss. Basic concepts of mass flow meters – Measurement characteristics of the instrument. Dynamic characteristics refer to the time response or frequency response properties of the output value when the input value of the measured quantity changes rapidly and abruptly. (1) Time domain: The time response characteristics of the output value when the input value to the object under test is a step signal. Its quality index can be expressed by a time constant. The time constant refers to the time it takes for the output value to reach 63% of its steady-state value, denoted by S. (2) Frequency domain: The frequency response characteristics of the output value when the input value of the object under test varies at a sine wave frequency. The characteristic in which the ratio of the flowmeter’s output value to its input value changes with frequency is known as the frequency response characteristic. Basic concepts of mass flow meters — Uncertainty in instrument measurements 1. Components of measurement error The characteristics of flow measurement errors can be classified into systematic errors, random errors, and negligence errors. 2. Uncertainty of measurement: (1) Class A assessment of standard uncertainty; (2) Class B assessment of standard uncertainty; (3) Combined standard uncertainty; (4) Expanded uncertainty; (5) Calculation and representation of measurement uncertainty. 3. Uncertainty in flow measurement: First, the Class A and Class B uncertainties of various parameters are determined, and then the combined standard uncertainty and expanded uncertainty are calculated. The development of mass flow measurement technology. The development, application, and demands of flow measurement technology are interdependent; applications and demands serve as the driving force behind the advancement of this technology. Currently, various methods for measuring mass flow rate, including indirect and direct measurement methods, are all in use to some extent. The indirect method for measuring mass flow rate accumulates significant errors due to the need to measure multiple intermediate parameters and then perform calculations and corrections. However, because it builds on traditional methods and is familiar to users, it is still widely used in situations where high measurement accuracy is not required. In particular, it is widely used in applications involving the measurement of gas mass flow rate or gas volume at standard conditions using a compensatory approach. The focus of development in mass flow measurement technology lies in direct mass flow measurement methods, in order to improve measurement accuracy and enable highly accurate and reliable measurements of various media under complex environmental conditions. In direct mass flow measurement methods, Coriolis mass flow meters have gained favor among users in various fields. This is because it can directly measure the mass flow rate of the fluid in the pipeline with high accuracy, features high stability and reliability, a large measurement range, and is suitable for use with highly viscous fluids.

In simple terms, it’s because the measurement principles used are different; mass flow meters utilize the Coriolis principle