Geometrical instruments – Indicator of direction of force traversing natural media – Level or plumb – terrestrial gravitation responsive
Reexamination Certificate
1999-12-07
2002-09-17
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Level or plumb, terrestrial gravitation responsive
C033S366120, C033S366150, C033S366190, C324S663000
Reexamination Certificate
active
06449857
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for level measurement and more particularly to a two-axis inclinometer and an integrated network of inclinometers capable of being centrally controlled and monitored.
BACKGROUND OF THE INVENTION
It is often desirable to measure the inclination of an object relative to one or more horizontal axes. A number of devices directed to this general purpose have been described.
A spirit level includes an enclosed tube that is partially filled with a liquid and has a gas bubble filling the remaining volume inside the tube. In a standard spirit level, a glass tube houses the liquid and is either slightly curved with its convex side upward or is ground with a curved inner bore. The glass tube is supported on a rigid base. Naturally, the gas bubble tends to seek the highest point in the tube containing the liquid and always comes to equilibrium at the same position whenever the base has the same slope with respect to the horizontal plane. Therefore, the user can measure inclination by observing the position of the bubble. However, there are obvious drawbacks to the spirit level, including its lack of precision as a result of its reliance on visual inspection of the bubble position.
A number of devices generally referred to as inclinometers or clinometers measure the magnitude and direction of inclination and produce an electrical signal as a function of inclination angle. Thus, an inclinometer can hold a dielectric or a conductive fluid in a chamber having two or more electrodes on or near opposite walls of the chamber, the electrodes being partially covered with fluid and with the fluid contact area on each electrode being dependent on the inclination angle of the chamber relative to gravity.
In a resistive inclinometer, the fluid has a specific conductivity and the resistance between the two electrodes varies with the contact area between the fluid and the electrodes. In a capacitive inclinometer, a dielectric fluid is used in the chamber. The electrical capacitance difference between the electrodes varies with the electrode-fluid contact area according to the inclination angle of the chamber. A common electrode can be provided such that capacitance of the common electrode is measured against that of each of the measuring electrodes.
Some prior art inclinometers have been described as having the various objectives of improving the utility, precision, accuracy, durability, efficiency or affordability of an inclinometer.
U.S. Pat. No. 4,167,818 to Cantarella et al. describes a single axis electronic inclination gauge fixed within a straight bar and having a digital output. A gravity dependent potentiometer cell operates in conjunction with a balancing bridge circuit to provide an analog voltage output whose magnitude is a function of inclination angle. This output is converted to digital values by a standard A/D converter. The cell is a sealed horizontally oriented cylindrical chamber partially filled with a semi-conductive fluid such as an alcohol. The chamber contains a central circular electrode opposing four symmetrically placed arcuate peripheral electrodes. This structure allows operation of the gauge from either of two orthogonal starting orientations. In operation, the center electrode has a function analogous to the slider of a variable resistor whereby its effective position in the resistance path between a pair of adjacent electrodes in circuit depends on the inclination angle of the chamber.
U.S. Pat. No. 4,811,491 to Phillips et al. describes an electronic capacitive inclinometer capable of measuring inclination in two axes. A non-conductive vertically oriented hollow outer cylinder has two pairs of symmetrically placed electrodes on its outside surface. An inner cylinder is spaced from the inner walls of the outer cylinder and functions as a common grounded electrode. A dielectric fluid is provided in the gap between the two cylinders. A pair of current sources charges each electrode of an opposing pair relative to the common electrode.
Analog output signals are generated as a function of the differential change in capacitance between,opposing electrodes. Their outputs are coupled to an amplifier by means of an RC low pass filter circuit. A clock-driven switch driver switches operation between the orthogonal pairs of electrodes.
U.S. Pat. No. 4,528,760 to Plummer describes a single-axis inclinometer having a common grounded electrode plate on one flat vertical outer face of a glass or plastic horizontally oriented cylinder housing and three symmetrically placed arcuate segment electrodes on an opposite outer face. A dielectric fluid partially fills the housing such that its level is always completely above one of the segment electrodes, thereby allowing inclination measurements for up to 360 degrees of inclination. Inclination is measured about a horizontal axis running through the cylinder outer surfaces. Each segment electrode is connected to a different oscillator circuit supplying a frequency to a terminal corresponding to the capacitance between the segment electrode and the common electrode. Comparison of frequency signals between terminals provides signals indicative of capacitance difference and a decode circuit is said to produce a corresponding,digital signal.
“Some inclinometers have sought-to avoid or compensate for the effects of temperature variations and electrochemical degradation. In a capacitive inclinometer, for example, temperature changes affect the dielectric constant of the sensor fluid. The cost of existing precision inclinometers, however, has been prohibitive. German Application No. DE 197 25 248 published Dec. 17, 1998 describes a two-axis capacitance inclinometer sensor provided with means for compensating for temperature changes in the environment of the sensor. The electrodes of the sensor area coated with a dielectric material such as TEFLON® polymer with the purpose of reducing screening by the sensor fluid to increase sensitivity and to improve efficiency. Temperature compensation is achieved by selecting a sensor fluid having a high dielectric constant and by including a comparison circuit wherein sensor data are adjusted based on temperature data.”
U.S. Pat. No. 3,992,951 to Erspamer et al. describes an analog resistive accelerometer having a horizontally oriented cylindrical housing and including a reference electrode to compensate for changes in electrolytic fluid temperature. The reference electrode is completely immersed at all times and therefore introduces a temperature-only dependent parameter to a signal amplifier in order to cancel the effects of temperature on resistivity measurements. A different compensation circuit is provided across the amplifier to detect any net DC voltage in the electrolytic fluid as a result of the reference circuit and to supply a compensating voltage to eliminate it and prevent polarization of the fluid.
“U.S. Pat. No. 4,912,662 to Butler et al. describes a capacitive inclinometer having aligned opposing sensor plates including corresponding conducting sectors. Pairs of opposing sectors from variable capacitors. A conductive grounded peripheral edge surrounds the plates to form a fluid cavity therebetween containing a conductive fluid. The sensor plates are preferably coated with a dielectric such as TEFLON® polymer. It is said that the dielectric coating effectively reduces the distance between the capacitive plates creating a high capacitance sensor without the manufacturing difficulty of actually placing the plates in close proximity to each other. Alternatively, the fluid is a dielectric and the plate coating is eliminated. The variable capacitors are placed in an oscillator circuit that has a frequency/period output in accordance with the capacitance of the capacitors. A microchip and memory are provided with a stored look-up table which is calibrated to the individual sensor for converting the output to units of inclination angle. It is said that the interface between the sensor and the microprocessor does not require a
Breiner & Breiner L.L.C.
Gutierrez Diego
Jagan Mirellys
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