Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
2000-03-14
2001-03-27
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
active
06205865
ABSTRACT:
BACKGROUND OF THE INVENTION
A mass flowmeter for flowing media of the above-mentioned type is known, for example from DE-A-41 24 295. As opposed to the mass flowmeters also known with two parallel Coriolis lines, which operate in the manner of a tuning fork (cf. e.g. U.S. Pat. No. 4,127,028), in the case of this known mass flowmeter, it is a problem that its center of mass oscillates back and forth, so that the possibility for introducing disturbing oscillations is greater, again resulting in loss of measurement accuracy.
In the case of the known mass flowmeters, in the case of which two parallel Coriolis lines are operated in the manner of a tuning fork, it is a problem that they have an increased flow resistance because of a complicated line course, and at the same time they can be cleaned only at increased expense. Precisely the last problem obtains also for mass flowmeters with parallel straight Coriolis lines (cf. e.g. DE C-34 43 234).
SUMMARY OF THE INVENTION
Thus the object of the invention is to improve the measuring accuracy of the known mass flowmeter for flowing media, which operates according to the Coriolis principle, while retaining its basic advantages.
The problem indicated and derived previously is solved in accordance with the invention by having the oscillation properties of the compensation cylinder essentially correspond to those of the Coriolis line.
The design of the mass flowmeter for flowing media in accordance with the invention ensures that the Coriolis line and the compensation cylinder oscillate opposite one another at least essentially in the manner of a tuning fork. In this way, the oscillation of the center of mass of the mass flowmeter is reduced to a small amount, if not entirely eliminated, by means of which the possibility of coupling disturbing oscillations is reduced and thus the measurement accuracy is increased.
The adjustment of the oscillation properties, in particular of the mass, the spring constant, and the attenuation constant, of the compensation cylinder to those of the Coriolis line is made significantly easier when the compensation cylinder and the Coriolis line consist of the same material. Titanium is used regularly as a material for the Coriolis line, so that titanium also is recommended as a material for the compensation cylinder.
A further advantageous design of the mass flowmeter in accordance with the invention consists in having the Coriolis line and the compensation cylinder located within a second compensation cylinder connected mechanically with the Coriolis line. The disclosure of DE A-41 24 295, for example, is to be consulted with respect to the design of this second compensation cylinder. For example, the Coriolis line can be located within the second compensation cylinder under initial tensile stress.
If, in accordance with one design of the invention, the oscillation generator is located between the compensation cylinder and the Coriolis line, this ensures that the compensation cylinder and the Coriolis line in each case oscillate in the manner of a tuning fork.
In the case of corresponding accommodation of the oscillation properties of the compensation cylinder and the Coriolis line, the oscillation opposite to each other in the manner of a tuning fork also is ensured when the oscillation generator is located between the second compensation cylinder and the compensation cylinder.
If, in accordance with a further advantageous design, the sensors are located between the compensation cylinder and the Coriolis line, an especially simple production of the mass flowmeter is ensured.
As an alternative to the design last described, it can be advantageous to locate the sensor between the second compensation cylinder and the Coriolis line, since in this way the influence of phase shifts of the oscillation of the first compensation cylinder is reduced. These phase shifts arise because the flowing medium flows only through the Coriolis line and not through the first compensation cylinder.
The phase shifts of the oscillation of the first compensation cylinder can be reduced in accordance with a further design of the invention by locating at least two control or correcting elements between the second compensation cylinder and the first compensation cylinder in order to eliminate just these phase shifts.
Since the oscillation properties of the first compensation cylinder do not exactly correspond to those of the Coriolis lines because of the usually non-uniform density of the flowing medium, it is advantageous to locate a correcting element between the second compensation cylinder and the first compensation cylinder in order to eliminate the medium density-dependent mass difference between the first compensation cylinder and the Coriolis line.
A particularly advantageous design of the mass flowmeter in accordance with the invention consists in having the first compensation cylinder form the second compensation cylinder at the same time. In this case, the single compensation cylinder must be designed in such a way that, on the one hand, it has essentially the same oscillation properties as the Coriolis line and, on the other hand, at the same time, for example, the Coriolis line is under initial tensile stress. In this case it is advantageous to make the single compensation cylinder out of Invar.
In particular, there are now a number of possibilities for designing and further developing the mass flowmeter for flowing media in accordance with the invention, which operates according to the Coriolis principle. For this purpose reference is made, on the one hand, to the dependent patent claims and, on the other hand, to the description of preferred embodiments in connection with the drawings.
REFERENCES:
patent: 4127028 (1978-11-01), Cox et al.
patent: 4803867 (1989-02-01), Dahlin
patent: 4823614 (1989-04-01), Dahlin
patent: 5365794 (1994-11-01), Hussain et al.
patent: 5398554 (1995-03-01), Ogawa et al.
patent: 5531126 (1996-07-01), Drahm
Cesari and McKenna
Hedstrom Corporation
Patel Harshad
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