Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Patent
1998-07-06
2000-10-31
Patel, Harshad
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
73861356, G01F 168
Patent
active
061385174
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a mass flowmeter for measuring by means of the Coriolis principle both mass and density of a fluid flowing in pipes and establishing oscillations in these pipes, said mass flowmeter comprising an inlet and an outlet for the fluid, between which is arranged at least one measuring pipe, said measuring pipe being provided with sensors for the detection of movements in the measuring pipe in the form of fluid flow through the measuring pipe, said sensors consisting of at least one magnet fixed to the measuring pipe and at least one coil fixed to a coil supporting plate.
U.S. Pat. No. 5,349,872 describes a device of this kind. The magnets are arranged on a first measuring pipe and a second measuring pipe, and the coils are arranged on a frame for the mass flowmeter. Various ways of arranging the magnets and coils and various types of coils are described in the document. Measurements made with this device, which are described in the document, depend on the way the magnets are arranged on the measuring pipes and the type of coils used. Generally, the signal size will depend on the strength of the magnet and the size of the coil, so that a strong magnet will only demand a small coil and vice versa, to obtain a given signal size. The embodiments shown in the document are all realised with magnets fixed to the measuring pipes to reduce the mass of the measuring pipes and to facilitate the mounting of the cables leading to the coils. The mass of the magnets is normally smaller than the mass of the coils.
However, all the device embodiments shown in the document mentioned above imply one considerable disadvantage. The measurement accuracy depends among others on the linearity of the movement sensor described. The linearity again depends on the construction of the coil and the magnet. The coil in the embodiments shown are all made with one single winding. This implies that to get a linear signal, the magnet must be made so that it creates a homogenous field in the spot where the magnet influences the coil. This increases the complexity of the magnet, the weight increases, and the demands on positioning of magnet and coil are increasing. Further, the device can only make accurate measurements at a limited oscillation of the measuring pipes, as the linearity of the voltage induced in the coils only extends over a limited deflection of the measuring pipes.
SUMMARY OF THE INVENTION
The object of the invention is, therefore, to create a device, which does not bear this disadvantage, in that a given measurement accuracy is maintained even for large oscillations of the measuring pipes, in that the linearity of the voltage induced in the coils extends over a larger deflection of the measuring pipes, even with a simple magnet embodiment. This purpose should be reached without increasing the demands on mounting tolerances and thus the costs for mounting of this device compared with known devices.
This object is reached by a mass flowmeter, which is characterised in that at least one coil comprises a first winding and a second winding, and that the first winding is wound in one direction around a longitudinal axis, that the second winding is wound in a different, and opposite in relation to the first winding, direction around the longitudinal axis, that the first winding and the second winding are arranged axially in relation to each other along the longitudinal axis, and that the first winding is connected in series with the second winding.
A coil having these characteristics and used in a mass flowmeter implies that a given measurement accuracy of the mass flowmeter will be maintained even at large deflections of the measuring pipe, and at the same time the demand for mounting tolerances will be maintained and thus not increased.
A preferred embodiment of the mass flowmeter according to the invention is characterised in that the mass flowmeter comprises a first measuring pipe and a second measuring pipe, that at least a first and a second coil are fixed to the frame of the m
REFERENCES:
patent: 4187721 (1980-02-01), Smith
patent: 4252028 (1981-02-01), Smith et al.
patent: 4756198 (1988-07-01), Levien
patent: 4781068 (1988-11-01), Pradelli
patent: 5301557 (1994-04-01), Cage et al.
patent: 5349872 (1994-09-01), Kalotay et al.
Birker Bertel
Hansen Henning Max
Laursen Mogens Bech
Danfoss A/S
Patel Harshad
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