Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With electromagnetic field
Reexamination Certificate
1998-09-03
2001-02-06
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With electromagnetic field
C324S125000, C324S114000, C324S143000, C073S732000
Reexamination Certificate
active
06184674
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
My present invention relates to indicating instruments, and more particularly to indicating instruments of the moving magnet type wherein a magnet is mounted on a shaft carrying a pointer one end of which is closely juxtaposed to a dial, and wherein an environing magnetic field is provided in the space provided by the shaft-mounted magnet and the direction of that magnetic field is varied in accordance with the momentary magnitude of a parameter whose magnitude is to be indicated on the dial by the pointer.
The present invention also relates to an apparatus for preventing the unwanted migration of fluid out of a chamber, including a chamber used to hold damping fluid in an indicating instrument, such as a moving-magnet or Bourdon-tube indicating instrument.
2. Description of the Prior Art
Moving magnet indicating instruments are well known in the prior art.
For example, a moving magnet indicating instrument of the cross-coil type is shown and described in U.S. Pat. No. 5,095,266, which was issued to Yukio Ohike and Tomohiro Sugiyama on Mar. 10, 1992. In the indicating instrument of this patent the magnetic field which environs the moving magnet is provided by electrical currents flowing through a pair of mutually perpendicular coils, said currents varying from moment to moment in accordance with the momentary magnitude of the quantity to be indicated.
Another moving magnetic indicating instrument of the cross-coil type is shown and described in U.S. Pat. No. 4,906,919, which was issued to Koichi Sato, Tatsuro Togawa and Toshiyuki Ohtake on Mar. 6, 1990.
Another type of moving magnet indicating instrument known in the prior art is typified by the differential pressure and flow instruments made and sold by Orange Research, Inc., of 140 Cascade Boulevard, Milford, Conn. 06460. In these instruments the magnetic field which environs the moving magnet, and which moves the pointer shaft and its associated dial pointer, is a permanent magnet which is moved with respect to the dial operating magnet by the fluid pressure or fluid flow the magnitude of which is to be indicated.
As is well known to those having ordinary skill in the moving magnet indicating instrument art, the moving magnet assemblies of such instruments, principally comprising the moving magnet, the shaft, and the dial pointer thereof, are characterized by low inertia and low friction, necessitating the provision of damping means. Further, due to the highly competitive economics of manufacturing and marketing of these instruments, such damping means must be as inexpensive and simple to assemble as possible. This requirement as led to the widespread adoption for this purpose of a small quantity of suitable damping fluid, such as silicone oil, disposed in the cavity formed by the housing of the instrument, containing the moving magnet, with no containment means to positively maintain the damping fluid within the housing.
Unfortunately, as is well known to those having ordinary skill in the art, there is a definite tendency for the damping fluid to migrate, via the clearance between the dial shaft and the surrounding portion of the instrument housing, to parts of the instrument where its presence is undesirable, such as the pointer, the dial face, and the lens of the instrument. Indeed, this is a problem with all indicating instruments that use damping fluids, including mechanical indicating instruments such as Bourdon tube indicating instruments.
Additionally, many of the prior art moving magnet indicating instruments are provided with pointer shafts which are of very small diameter, as compared with their overall length.
While the use of such small diameter pointer shafts saves weight and cost, it results in certain disadvantages, such as the inadvertent binding of the shaft, and the lack of sufficient contact surface area between the shaft and the wall of the central hole in the moving magnet, into which the shaft is press-fitted. Further, the small diameter of the pointer shaft severely limits the area of the shoulder turned therein which is used as part of the thrust bearing which prevents movement of the shaft into and out of the opening in the housing in which its pointer-bearing end is journaled.
It is believed that the documents listed immediately below contain information which is or might be considered to be material to the examination of this patent application.
U.S. Pat. Nos. 3,494,203, 3,778,711, 4,402,335, 4,492,920, 4,724,601, 5,017,862, 5,038,099
The term “prior art” as used herein or in any statement made by or on behalf of applicant means only that any document or thing referred to as prior art bears, directly or inferentially, a date which is earlier than the effective filing date hereof.
No representation or admission is made that any of the above-listed or cited documents is part of the prior art, or that a search has been made, or that no more pertinent information exists.
A copy of each of the above-listed or cited documents is being supplied to the United States Patent and Trademark Office herewith.
SUMMARY OF THE INVENTION
Accordingly, it is an object of my present invention to provide leak preventing means for preventing the leakage of silicone damping oil from inside the housings of moving magnet indicating instruments, through the pointer-shaft-receiving holes in said housings.
It is another object of my present invention to provide leak preventing means which achieve the foregoing object and can be added to a wide range of prior art moving magnet indicating instruments with very little or no extra manufacturing costs.
It is another object of my present invention to provide fluid migration barriers to prevent leaking of fluid from any indicating instrument, including both moving magnet indicating instruments and mechanical indicating instruments, such as Bourdon tube indicating instruments.
It is a further object of my present invention to provide fluid migration barriers to prevent the unwanted migration of a fluid out of any cavity, wherein the fluid has a tendency to migrate over a surface.
It is yet another object of my present invention to provide double-faced moving magnet indicating instruments having first and second dial faces, one on each side of the instrument, in which both dial-carrying sides are provided with leak preventing means which prevents the leakage of damping oil from the housings of said instruments through either of said dial shaft holes.
It is a further object of my present invention to provide double-pointer moving magnet indicating instruments each of which instruments has a single dial face with which two different pointers coact, each pointer indicating, on an associated scale on said dial face, the magnitude of a different input signal or measured quantity. Said dial face may, in some embodiments, bear a single scale or two superimposed scales.
Other objects of my present invention will in part be obvious and will in part appear hereinafter.
My present invention, accordingly, comprises the apparatus embodying features of construction, combinations of elements, and arrangements of parts, all as exemplified in the following disclosure, and the scope of my present invention will be indicated in the claims appended hereto.
In accordance with a principal feature of my present invention moving magnet indicating instruments which contain damping fluid are provided with one or more migration barriers by means of which migration of the damping fluid over the inside surfaces of the housing of said instrument, and over the surfaces of the parts contained in said housing, are prevented.
In accordance with another principal feature of my present invention each of said migration barriers is a ridge which is raised on the inner surface of the instrument housing, or on the surface of a part contained therein.
In accordance with yet another principal feature of my present invention each of the ridges of certain embodiments of my invention are of toroidal configuration and of generally triangular cross-section.
In accordance wit
Dorsey & Whitney LLP
Patidar Jay
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