Zero calibration of mass flow meter

Just calibrate the zero point online, and the density will be automatically corrected

Search on your own for the principle of mass flow meters; they measure Coriolis force and are independent of density

At the very least, we should mention which manufacturer it is, right?

Sometimes it can remain accurate even without recalibration, with minimal drift

It would need to be calibrated based on the material. Normally, manufacturers use a certain standard substance for calibration, rather than a specific medium. I’m not sure what impact it would have on the measurements if calibration isn’t done

Does that mean that once the material is calibrated once, any changes in the material will automatically adjust its density, so no further calibration is needed?

A mass flow meter’s measurement system, as described in encyclopedias, consists of a sensor and a transmitter for signal processing. The Rosemount mass flow meter is based on Newton’s second law: Force = mass × acceleration (F=ma). When a particle with mass m moves at velocity V within a pipe that rotates at an angular velocity ω around the P-axis, the particle experiences two types of acceleration and corresponding forces: (1) normal acceleration, or centripetal acceleration αr, whose magnitude is equal to 2ωr, and it acts toward the P-axis; (2) tangential acceleration αt, or Coriolis acceleration, whose value is equal to 2ωV, and its direction is perpendicular to αr. Due to the combined motion, a Coriolis force Fc=2ωVm acts on the particle in the αt direction, while the pipe exerts an opposite force -Fc=-2ωVm on the particle. When a fluid with density ρ flows at a constant velocity V through a rotating pipe, any segment of the pipe of length Δx is subjected to a tangential Coriolis force ΔFc: ΔFc=2ωVρAΔx (1), where A is the cross-sectional area of the pipe. Due to the relationship mq=ρVA, we have: ΔFc = 2ωqmΔx (2). Therefore, by directly or indirectly measuring the Coriolis force of the fluid flowing in the rotating tube, it is possible to determine the mass flow rate. Principle of density measurement: One end of the flow tube is fixed, while the other end is free. This structure can be regarded as a mass/spring system in which a weight is suspended from a spring; once set in motion, this mass/spring system will vibrate at its resonant frequency, which is related to the mass of the weight. The flow tube of a mass flow meter vibrates at its resonant frequency through a driving coil and a feedback circuit; the resonant frequency of the vibrating tube is related to its structure, material, and mass. The mass of the vibration tube consists of two parts: the mass of the vibration tube itself and the mass of the medium inside it. Once each sensor is manufactured, the mass of the vibration tube itself is determined. The mass of the medium inside the vibration tube is equal to the product of the density of the medium and the volume of the vibration tube; since the volume of the vibration tube remains constant for sensors of any given diameter, the vibration frequency is directly related to the density. Therefore, for sensors with fixed structures and materials, the density of the medium can be determined by measuring the resonance frequency of the flow tube. A pair of signal detectors utilizing flow measurement can yield a signal representing the resonant frequency; the signal from a temperature sensor is used to compensate for changes in the stiffness of the flow tube caused by temperature variations. The vibration period is determined by measuring the vibration period of the flow tube along with the temperature, while the medium density is measured based on the linear relationship between density and the vibration period of the flow tube, along with standard calibration constants. When a Coriolis mass flow sensor uses a vibrating tube to measure density, the stiffness of the tube, its geometric structure, and the mass of the fluid flowing through it all determine the natural frequency of the tube assembly; thus, the fluid density can be determined from the measured frequency of the tube. The transmitter uses a high-frequency clock to measure the time of the vibration cycle; the measured values are digitally filtered, and compensation is applied for changes in the stiffness of the pipeline caused by operating temperature, which in turn leads to changes in the natural frequency. The density of the process fluid is then calculated using sensor density calibration coefficients.