Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-10-21
2001-04-03
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C324S207160, C336S045000
Reexamination Certificate
active
06211667
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device for measuring the displacement of stems of valves; more particularly, the invention relates to an electronic position transmission device adapted to transmit, according to a linear law, the position of the stem of valves, such as adjustment valves or rotary valves.
As it is known, in the field of adjustment valves it is particularly important to know at all time the position of the stem of the valve in order to know the state of the valve time by time.
Position transducers currently used for this purpose suffer the drawback that they do not offer high measurement precision and are further affected by mechanical displacements caused not by the angular movement of the stem of the valve whose position is to be detected but, for example, by thermal expansions.
It is commonly known to use a rotating potentiometer as a position transducer; however, such potentiometer entails the drawback that it has components which are subject to friction wear and also requires shielding for protection against the inevitable sparks generated during its operation.
Another type of position transducer that is currently used is a differential transformer, which however entails the drawback of being expensive.
SUMMARY OF THE INVENTION
The main aim of the present invention is to provide a device for measuring the displacement of stems of valves, which provides a highly precise measurement.
Within the scope of this aim, an object of the present invention is to provide a device for measuring the displacement of stems of valves, whose obtainable measurement allows to minimize the effects of mechanical displacements not caused by angular movement, such as for example thermal expansions.
Another object of the present invention is to provide a device for measuring the displacement of stems of valves, which allows to obtain a linear measurement signal.
Another object of the present invention is to provide a device for measuring the displacement of stems of valves, having a modest power consumption.
Another object of the present invention is to provide a device for measuring the displacement of stems of valves, which is highly reliable, relatively easy to manufacture and at low costs.
This aim, these objects and others which will become apparent hereinafter are achieved by a device for measuring the displacement of stems of valves, characterized in that it comprises a spindle coupled to a stem of a valve and provided with two inductive pickups, each inductive pickup comprising a fixed part and a movable part constituting a variable inductor, which, following a displacement of said stem and a rotation of the spindle coupled thereto, generates an inductance variation of the electric circuit associated thereto;
electronic excitation and detection means adapted to convert said inductance variations into a pair of digital signals whose difference is indicative of the displacement of the stem.
In a further aspect, the present invention relates to a method for measuring the displacement of stems of valves, characterized in that it comprises the steps of:
transforming the displacement of the stem into a rotation of a spindle coupled to said stem, said spindle being provided with two inductive pickups, each inductive pickup comprising a fixed part
4
and a movable part
6
constituting a variable inductor, which, following the displacement of said stem and a rotation of the spindle coupled thereto, generates an inductance variation of the electric circuit associated thereto;
converting, by electronic excitation and detection means, said inductance variations into a pair of digital signals;
carrying out the difference between said pair of digital signals, said difference being indicative of the displacement of the stem.
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Patent Abstract of Japan vol. 013, No. 455 (M-879), Oct. 13, 1989 & JP 01 176880 A (Toto Ltd), Jul. 13, 1989 * abstract *.
Borelli Riccardo
Volonterio Eugenio
ABB Kent Taylor S.p.A.
Josif Albert
Modiano Guido
O'Byrne Daniel
Patidar Jay
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