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Principle of Measurement
Principle of Measurement

    The structure of KLB-CMFI Coriolis mass flowmeter is a two-pipe structure, the measuring principle is: When the fluid is flowing, it is led through two parallel tubes. An actuator induces a vibration of the tubes. The two parallel tubes are counter-vibrating, to make the measuring device less sensitive to outside vibrations. The actual frequency of the vibration depends on the size of the mass flow meter, and ranges from 80 to 1000 vibrations per second. The amplitude of the vibration is too small to be seen, but it can be felt by touch. When there is mass flow, there is some twisting of the tubes. The arm through which fluid flows away from the axis of rotation must exert a force on the fluid to increase its angular momentum, so it is lagging behind the overall vibration. The arm through which fluid is pushed back towards the axis of rotation must exert a force on the fluid to decrease the fluid's angular momentum again, hence that arm leads the overall vibration. The inlet arm and the outlet arm vibrate with the same frequency as the overall vibration, but when there is mass flow the two vibrations are out of sync, the inlet arm is behind, the outlet arm is ahead. The two vibrations are shifted in phase with respect to each other, and the degree of phase-shift is a measure for the amount of mass that is flowing through the tubes. Through the medium of different density, the vibration frequency of the different, which can calculate the medium-density solution. The platinum resistance installed in the pipe may be indirect measurement of the temperature medium.

     Every meter consists of two parts: the sensor (primary meter) and the transmitter (secondary meter).
     The sensor (primary meter) is machinery part of mass flow meter. There are a vibrator, two displacement sensors and a temperature sensor in it.
     The transmitter (secondary meter) is display part of the meter, also is electrical part. There are power supply, analog circuits, digital circuits, displayer, and output circuits and so on in it. Its foundational functions are receiving and regulating the electrical signal from sensors, directly getting mass flow, temperature and density after regulating, and calculating volume flow and other need parameters from known parameters. It can display, output, store and long distance transmit, and you can modify the parameters of flow meter. There is a diode safety barrier in transmitters; the function of the diode safety barrier is safeguard to isolating explosion.
     As the composite explosion-proof flow meter, the sensor (primary meter) is essential safety; the transmitter (secondary meter) is explosion isolated. The sensor and the transmitter may all operate under hazardous area.
     As the essential safety flow meter, the sensor (primary meter) can operate under hazardous area, the transmitter (secondary meter) must only operate under prescriptive safety area (see section 3.2), forbidden to operate under hazardous area.


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