Geometrical instruments – Indicator of direction of force traversing natural media – Level or plumb – terrestrial gravitation responsive
Reexamination Certificate
2000-04-06
2001-06-26
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Level or plumb, terrestrial gravitation responsive
C033S366210
Reexamination Certificate
active
06249984
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electrochemical transducers and, more particularly, to electrolytic tilt sensors.
BACKGROUND OF THE INVENTION
Electrolytic tilt sensors include devices that provide output signals proportional to the angle of tilt and/or the direction of tilt when included as part of an appropriate electrical circuit. Tilt sensors were originally developed for weapons delivery and aircraft navigation and are now used in applications such as oil drilling, construction laser systems, automotive wheel alignment, seismic and geophysical monitoring, virtual reality systems, and robotic manipulators.
Most conventional electrolytic tilt sensors generally comprise a housing, or envelope, made of a non-conductive material, such as glass. The envelope is partially filled with an electrolytic solution and encloses a plurality of electrodes, which are partially immersed in the electrolytic solution when the tilt sensor is in its upright (i.e., zero tilt or electrical null) position. One of the electrodes, typically a center electrode, is a common electrode, and the remaining electrodes are sensing electrodes, which are typically grouped in one or more pairs that define one or more distinct tilt axes in conjunction with the center common electrode.
As the tilt sensor is tilted with respect to the horizontal, each of the sensing electrodes becomes more or less immersed in the electrolytic solution while the surface of the solution remains level with reference to the horizontal. The increase or decrease in immersion results in a corresponding change in impedance between any one of the sensing electrodes and the common electrode. This impedance change is measured by an electrical circuit and correlated to a tilt angle and/or tilt direction, depending on the number of sensing electrodes and the type of electrical circuit being used.
A shortcoming of glass-enclosed tilt sensors is that they are relatively fragile due to their glass construction. Glass-enclosed sensors must be handled with care and protected in special containment packages. They are costly to manufacture and generally use precious metal electrodes. Moreover, glass enclosed sensors may not be suitable for certain applications where a tilt sensor having a more robust enclosure is required.
In addition to electrolytic tilt sensors having non-conductive envelopes, tilt sensors having partially metallic envelopes, such as those disclosed in U.S. Pat. No. 5,630,280 to Crossan, Jr. and German Patent Publication No. DE 40 25 184 A1 to Geisel, have been described. Generally, such tilt sensors have two or four sensing electrodes extending into a chamber defined by the envelope, which comprises a metallic containment vessel and a header made of a non-conductive material. The metallic containment vessel functions as the common electrode while the header supports the sensing electrodes and insulates them from the metallic containment vessel.
A shortcoming of the Crossan, Jr. tilt sensor is that the relatively large glass seal can be susceptible to cracking caused by rough handling, age, harsh environment, and the like, which would lead to failure of the tilt sensor due to leakage of the electrolytic solution. In addition, the interface between the dissimilar materials of the seal and the containmnent vessel may provide a less than desirable seal, particularly if the tilt sensor were exposed to elevated temperatures.
At elevated temperatures the pressure inside the tilt sensor increases due to expansion of the gas and vaporization of the electrolytic solution inside the tilt sensor. When the temperature becomes too high, vaporized solution can escape between the seal and the containment vessel. Loss of even only part of the electrolytic solution will detrimentally affect the operation of the sensor.
The Geisel tilt sensor has a compression-fit O-ring gasket located between the containment vessel and the insulating header. A shortcoming of the gasket is that it is subject to deterioration over time, which may eventually cause the electrolytic solution to leak from the sensor. The Geisel tilt sensor also may be susceptible to vapor leakage and pressure loss due to failure of the mechanical seal at elevated internal pressures resulting from exposure to elevated temperatures. In addition, a gasket-type seal requires the additional gasket component, which adds to the complexity, difficulty, and cost of manufacturing the tilt sensor. Moreover, the Geisel electrodes appear to be adhesively bonded to the insulating header. Such adhesive bonds would be susceptible to destruction by the solvents of the electrolyte, particularly at elevated operating temperatures. Furthermore, neither the Crossan, Jr. nor Geisel tilt sensor is operable unless the containmnent vessel functions as the common electrode.
Due to the shortcomings of the above-mentioned tilt sensors, there is a need for a tilt sensor having a robust envelope and a highly reliable seal between the header and the containment vessel. In addition, there is a need for a tilt sensor having a metallic envelope and a center common electrode extending into the chamber defined by the envelope.
GLOSSARY
1. Acquiescent bath (still bath): An electrolytic cell, which is not agitated and depends solely on ionic movement by diffusion mechanisms.
2. Bipolar electrode: An electrode which is not directly connected to the power supply but is so placed in the solution between the anode and the cathode that the part nearest the anode becomes cathodic and the part nearest the cathode becomes anodic.
3. Concentration gradient: A thin region of electrolyte directly adjacent to the electrode which is primarily responsible for polarization effects.
4. Convection: The thermal energy process by which mass is transmitted through a material by bulk motion of the media itself.
5. Diffusion: In chemistry, the spontaneous migration of substances from regions where their concentrations are high to regions where their concentrations are low.
6. Electrical Null: Indicated by a minimal or zero electrical output value.
7. Electrolytic cell: (Electrolytic cell, bath, or tank with electrodes and electrolyte) A unit apparatus designed for carrying out an electrochemical reaction; includes a vessel, two or more electrodes, and one or more eletrolytes.
8. Flux: The presence of a force field in a specified physical medium, or the flow of energy through a surface; The geometric orientation of the lines of flux in the vicinity of an electrically charged object; Described as lines surrounding a current carrying conductor as they appear in a plane perpendicular to a conductor; An electrostatic field between two oppositely charged fields in a plane containing the centers of both poles.
9. Linearity (%): Specifying a given straight line as a standard, the proximal values of a calibration curve to that line. Linearity may be expressed as maximal deviation of the calibration curve from that specified line.
10. Mechanical null: The sensor's physical housing reference relationship to the electrical null.
11. Noble (metal or potential): A noble metal is one for which the equilibrium in the reaction M→M
+
+ne (where n=a low integer; e=the electron) is toward the left; a noble metal does not readily tend to furnish ions, and therefore does not dissolve readily, nor easily enter into such reactions as oxidations, etc. A noble potential is the electrode potential of a noble metal.
12. Null drift, electrical: A fluctuation of a stationary sensor's electrical output at the null position over time.
13. Polarization: The change in the potential of an electrode during electrolysis, such that the potential of an anode always becomes more noble, and that of a cathode less noble, than their respective static potentials. Equal to the difference between the static potential and dynamic potential.
14. Shield (verb): To alter the normal current distribution on an anode or cathode by the interposition of a conductor or non-conductor.
15. Shield (noun): A conducting or non-condu
Barsky Barry E.
Burgess Lester E.
Kull Francis R.
Bennett G. Bradley
Drinker Biddle & Reath LLP
The Fredericks Company
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