The Coriolis mass flowmeter measures flow by detecting the distortion of the vibrating tube caused by Coriolis force. Its core principle is based on the combination of Coriolis effect and Newton's second law. The specific process is as follows:
1. Excitation and initial state of vibration tube
The sensor of the flowmeter adopts vibration tube structures such as U-shaped and S-shaped, and is driven by an electromagnetic drive coil to vibrate at high frequencies (frequency of about 80Hz, amplitude less than 1mm).
When there is no fluid flowing through, the vibrating tube only performs the main vibration (vertical vibration above and below), and the vibration signals recorded by the electromagnetic signal detectors on both sides are in phase.
2. Coriolis force caused by fluid flow
When fluid flows into the vibrating tube, it is forced to participate in the motion of the vibrating tube. According to Newton's second law, fluid flow generates a Coriolis force proportional to the mass flow rate (Fc=2 ω Vm, where ω is the angular velocity of vibration, V is the fluid velocity, and m is the fluid mass).
Twisting phenomenon of vibrating tube: During the vibration cycle, the fluid exerts an additional force in the opposite direction on the vibrating tube. For example, when a vibrating tube vibrates upwards, the incoming fluid resists upward movement and exerts a downward force on the tube wall; The flowing fluid resists downward movement and exerts upward force. This torque causes periodic distortion of the vibrating tube (Coriolis phenomenon), and the amount of distortion is proportional to the mass flow rate.
3. Phase difference detection and flow calculation
The distortion of the vibrating tube causes a difference in vibration phase between the inlet and outlet. Electromagnetic signal detectors on both sides record vibration signals and calculate the phase difference（
ΔT）。
The relationship between time difference and flow rate: The phase difference Δ T is proportional to the mass flow rate, and the mass flow rate can be directly calculated using the formula Qm=K ⋅Δ T (where K is the flow rate calibration coefficient).
Optimization of digital signal processing: Using digital signal processing (DSP) technology to filter noise, improve phase difference detection accuracy, and respond 2-4 times faster than traditional analog signal processing.
4. Temperature compensation and density measurement
Temperature changes can affect the rigidity of the vibrating tube, which in turn affects the amount of distortion. The transmitter monitors temperature in real-time through a platinum resistance thermometer and adjusts the flow calculation model to eliminate temperature interference.
The resonant frequency of the vibrating tube is related to the fluid density (ρ∝ f2), and the fluid density value can be synchronously output by measuring the resonant frequency.