Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2000-02-14
2002-11-26
Noori, Max (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S728000
Reexamination Certificate
active
06484586
ABSTRACT:
This invention relates to an differential pressure transducer which is especially suited for measuring the differential pressure in a severe industrial environment.
PRIOR ART
A differential pressure transducer is defined as a measurement means for measurement of differential pressure.
Differential pressure transducers are widely used for example in the chemical industry, food industry, aviation industry, in water treatment plants, etc. for purposes of among others flow measurement in flowing media, the control of filters, speed measurement in aircraft or water craft. The necessity of precise measurement of small differential pressures, typically roughly 100 mbar, around a high absolute (conventionally static) pressure of for example 100 bar, has led to development of relatively expensive and complex pressure transducers, since these devices on the one hand must demonstrate their serviceability in the transfer from ambient pressure to high absolute operating pressure and on the other hand must be sensitive enough to be able to measure small differential pressures with the desired accuracy.
WO 96/41141 discloses a pressure transducer in which a measurement membrane of electrically conductive material such as steel divides a measurement chamber into two measurement spaces. The membrane can be exposed to measurement pressures which yield a differential pressure in the two measurement chambers and it is deflected by the differential pressure from its neutral position. In one measurement chamber wall opposite the membrane there is a coil. Relative movements between the coil and membrane are measured via measuring inductance.
In pressure transducers of this type the problem is that, as a result of the elasticity of the measurement membrane, which is linear only in a narrow range, for larger deflections of the measurement membrane there is no longer a linear relationship between the change of the differential pressure and the corresponding change of inductance. Furthermore, there is the danger of inelastic deformations of the membrane which adulterate the measurement results over the long term, for which reason the long term serviceability of the pressure transducer is not ensured. In addition, temperature changes and/or corrosion can significantly change the material properties of the membrane; this can lead to further measurement errors.
DE-A1-31 06 835 describes a differential pressure measurement device which has a measurement chamber which is divided into two measurement spaces by a measurement membrane. The measurement chamber is hermetically sealed against the medium to the outside by means of separation membranes and the differential pressure can be measured in it. To transfer the differential pressure to be measured from the separation membranes to the measurement membrane, the two measurement spaces between the measurement membrane and the respective separation membrane are filled with oil. The measurement membrane in its center has a semiconductor sensor with which the deflection of the measurement membrane from its neutral position is measured. To prevent mechanical overload of the semiconductor sensor there is a compensation device which is coupled via a mechanical connection to the semiconductor sensor and thus the measurement membrane in order to counteract the deflection caused by the differential pressure. In the differential pressure measurement device as claimed in this patent the problem of mechanical overloading of the measurement membrane is reduced.
However, the differential pressure measurement means as claimed in DE-A1-31 06 835, as also otherwise all other known pressure transducers, has a complicated and expensive structure; this makes it unsuited for economical production in large series. At the same time the force of gravity in all known pressure transducers with a measurement membrane represents another error source in that under the influence of gravity the measurement membrane can already be deformed as a result of its inherent weight; this results in an error in pressure measurement which is dependent on the position of the pressure transducer.
DESCRIPTION OF THE INVENTION
The object of this invention is to make available a differential pressure transducer which is structurally simple, which can be economically produced in large series, and which is long-lived and itself enables reliable differential pressure measurements under ambient conditions which are severe with respect to corrosion and temperature.
The differential pressure transducer according to the invention has a measurement chamber which is defined by a housing and which is divided by a membrane device into a first measurement space which can be exposed to a first measurement pressure and a second measurement space which can be exposed to a second measurement pressure. The membrane device comprises at least one measurement membrane, the membrane device being arranged and made such that a deflection force which is engendered by the first measurement pressure and the second measurement pressure causes deflection of the measurement membrane from its neutral position. The pressure transducer furthermore has a deflection sensor means for measuring deflection of the measurement membrane from its neutral position and for producing a deflection signal depending on this deflection. The pressure transducer according to the invention is characterized in that it furthermore has an electromagnet arrangement which comprises magnet means and a microengineering current-carrying coil, and an electrical switching arrangement. The electromagnet arrangement is made to produce a magnetic force which couples the measurement membrane to the housing and the electrical switching device is used to produce a coil current depending on the deflection signal such that the magnetic force acting on the measurement membrane essentially compensates for the deflection force which is caused by the differential pressure and which acts on the measurement membrane. The coil current for producing the magnetic compensation force represents a measure of the differential pressure. The current intensity of the coil current is output as the output quantity of the pressure transducer.
Microengineering is defined as the means and processes which are employed to use and/or produce (preferably in series) extremely small technical devices or equipment. In microengineering the aspect of production, especially series production, is just as important as that of the function of a microengineering device. Microengineering components (for example, the coil of the pressure transducer as in the invention) therefore often have essentially flat, two-dimensional structures. They can be produced by means of methods of planar technology, especially printing processes (for example screen printing in thick film technology, vapor deposition in thin film technology, UV lithography).
In the context of microengineering, the term “small”, at least in mechanical and/or electromechanical devices, means that their main dimensions are in the centimeter or subcentimeter range.
A “magnetic force” is the force which an electrical conductor or permanent magnet experiences in a magnetic field and “magnetic means” are means of electrically conductive and/or magnetic material which can experience a magnetic force in a magnetic field.
The differential pressure transducers known to date are not suited for production with methods of planar technology. They have components with structures which are essentially three-dimensional and their production is structurally complex. In the pressure transducer as claimed in DE-A1-31 06 835 this applies especially to the compensation device which comprises an electromagnet with a coil and a permanent magnetic armature, and the two have structurally complex three-dimensional structures. Conversely, the microengineering (and thus flat) coil of the differential pressure transducer according to the invention can be produced with means and methods of microengineering. In this way the possibility of economical, large-series production of th
Dutoit Bertrand
Friedrich Andreas
Hug Kurt
Popovic Radivojc
Haenni Instruments AG
Noori Max
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