Sep. 12, 2020
The working principle of mass flow meter
The Coriolis mass flowmeter uses the principle of modulation of the fluid mass flow rate on the vibration of the vibrating tube. The sensor consists of a vibrating tube (measuring tube), a signal detector, a vibration driver, a supporting structure and a shell. The transmitter is based on a microprocessor, which provides driving force to the sensor and converts the signal measured by the sensor into a mass flow signal. It also has the function of compensating and correcting the mass flow and density measurement according to temperature parameters. The output current signal or frequency signal can communicate with DCS according to a certain protocol.
Mass flow meter installation
1) The mass flowmeter works based on the principle of vibration, and in the process of its work, electromagnetic technology is used for vibration excitation, torsion angle detection and detection signal processing, so the mass flowmeter installation position cannot be large. The vibration source of this type cannot be installed near transformers, motors and other equipment that generate strong magnetic fields to prevent external interference from affecting its normal operation.
2) There is no requirement for straight pipe section in the installation of mass flowmeter, but stress should be avoided when connecting the sensor and pipe. If the concentricity between the sensor and the pipeline centerline is deviated during the installation of the mass flow meter, it will cause stress in the vibrating tube, which will cause pressure, tension, or shear force to affect the alignment of the pipeline and cause the asymmetry of the detection probe , Resulting in zero point changes and affecting measurement accuracy. If the concentricity deviation between the pipeline and the sensor is too large, the zero point may not be adjusted. Therefore, reinforcement measures should be taken to stabilize the pipeline near the instrument. When installing the flow sensor, a soft connection method should be adopted as much as possible, and the flange connection screws should be evenly and symmetrically tightened. In order to reduce the influence of residual stress, the flow sensor must be zero-point calibrated after installation. In order to facilitate the installation and zero adjustment of the mass flowmeter, stop valves should be installed at the front and back of the mass flowmeter.
3) The connection cable between the sensor and the transmitter should use the manufacturer's special cable; the transmitter receives low-level signals, so the cable should not be too long. When installing the transmitter, make sure that the partition used to separate the intrinsically safe sensor cable from the power supply and output cable is installed in place; ensure that the sensor junction box and the transmitter housing are sealed to avoid short-circuits that may cause measurement errors or flowmeter failures.
4) Choose different sensor installation orientations according to the different properties of the fluid, and always keep the fluid in the sensor flow tube full. The U-shaped tube of the mass flow meter for gas feed measurement faces upwards to avoid accumulation of condensate in the measuring tube; the U-shaped tube of the mass flow meter for liquid feed measurement faces downwards to avoid gas accumulation in the measuring tube.
The above information is provided by mass flowmeter manufacturer.