Measuring and testing – With fluid pressure – Dimension – shape – or size
Patent
1991-07-11
1993-05-04
Williams, Hezron E.
Measuring and testing
With fluid pressure
Dimension, shape, or size
73 375, G01B 13008
Patent
active
052070891
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring the control cross section area of a nozzle. The so-called Rota method, in which a flow passes through the nozzle in a supercritical ratio P.sub.A /P.sub.E =0.52 (for air), was previously used for such measurements. In so doing, a floating-body flow meter is arranged in front of or in back of the test sample, depending on whether vacuum or overpressure method is utilized. Such a method has the disadvantage that it is relatively time consuming and not particularly accurate, requires a greater quantity of models for every nozzle type, and is difficult to automate. It is further known to measure the mass flow e.g. by means of a caloric flow meter. In this case, the pressure and temperature of the in-flowing medium (that is, on the high-pressure side of the test sample) is additionally measured and kept constant in a corresponding manner. Such a measuring method is relatively complicated and slow.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for measuring a control cross-section area of a nozzle, that enables very short measuring times and requires no pressure measurements.
In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method for measuring a control cross-sectional area of a nozzle by means of a pneumatic through-flow method with supercritical pressure ratio, in accordance with which the flow passing through the nozzle is measured as volume flow on its input side.
In accordance with another feature of the present invention the volume flow can be determined by means of differential pressure measurement at a resistance distance through which a laminar flow passes. The resistance distance can comprise one or more tubes which are connected parallel.
Still another feature of the present invention is that the vacuum method can be carried out by means of a vacuum pump. On the other hand, the overpressure method can be used in the inventive method for measuring the control cross-section area.
A further feature of the present invention is that deviations of the temperature of the test medium from a reference temperature are detected by means of a temperature sensor and taken into consideration in a correction factor.
Finally, the measurement variables of differential pressure, temperature and possibly additional auxiliary variables are determined and processed in a computer-controlled test device. This method makes use of the physical advantages of the supercritical through-flow and accordingly reduces the influence of errors. The quantity of measurement variables required for determining the sought for control cross section area is reduced to only one essential measurement variable, namely, that of the volume flow; the temperature is required only for a correction factor. Moreover, the method results in a linear characteristic line of measuring values, enables a large measuring range and is also easy to check.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operations, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view schematically showing a measuring device in accordance with the present invention;
FIG. 1a is a pressure diagram of the measuring device of FIG. 1;
FIG. 2 is a view substantially corresponding to the view of FIG. 1 but showing a measuring device in accordance with another embodiment in accordance with the present invention; and
FIG. 2a is a pressure diagram of the measuring device of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the measuring device according to FIG. 1, in which the vacuum method is used,
REFERENCES:
patent: 3838598 (1974-10-01), Tompkins
patent: 4161119 (1979-07-01), Brandt, Jr.
patent: 4753114 (1988-06-01), Jones, Jr. et al.
patent: 5961349 (1990-10-01), Tanis
"Flow-Its Measurement and Control in Science and Industry" vol. 1, Part 1, 1974, pp. 263-267.
Abt Jurgen
Banzhaf Werner
Felten Gerhard
Kuhn Ulrich
Lemperle Gerold
Ashraf Nashmiya
Robert & Bosch GmbH
Striker Michael J.
Williams Hezron E.
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