Geometrical instruments – Indicator of direction of force traversing natural media – Level or plumb – terrestrial gravitation responsive
Reexamination Certificate
2000-09-28
2002-09-24
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Level or plumb, terrestrial gravitation responsive
C374S006000, C033S315000
Reexamination Certificate
active
06453571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to tilt sensors, and more particularly, to a thermocouple tilt sensor.
2. Description of the Related Art
Tilt sensors are generally known in the art. Specifically, Crossan, Jr. (U.S. Pat. No. 5,630,280) and Seipp, Jr. et al. (U.S. Pat. No. 5,852,878) disclose two common forms of electrolytic tilt sensors. Electrolytic tilt sensors are devices that change their electrical properties when tilted as a result of the interaction between an electrolyte and a plurality of electrodes contained therein. For example, known electrolytic tilt sensors provide an output voltage proportional to the tilt angle and a phase indicative of tilt direction when the sensor is configured as part of an appropriate electrical circuit. In addition, the tilt sensors can be configured to measure acceleration. In a tilt sensor configuration, the output voltage changes based on the change of impedance between the electrodes. The impedance between each electrode changes as the tilt angle changes and either more or less electrolytic fluid surrounds the electrodes.
Referring now to
FIG. 1
, there is shown a three-dimensional representation of a dual axis electrolytic tilt sensor
100
according to the prior art. Tilt sensor
100
is comprised of a cylindrical housing
120
that is partially filled with an electrolytic solution
140
. Within cylindrical housing
120
are disposed a common electrode
150
, a pair of first axis electrodes
160
and
170
and a pair of second axis electrodes
180
and
190
, wherein common electrode
150
, first axis electrodes
160
,
170
and second axis electrodes
180
,
190
are partially immersed in electrolytic solution
140
.
When sensor
100
is tilted, the surface of electrolytic solution
140
remains in a horizontal level plane with respect to gravity, and electrolytic solution
140
shifts with respect to the electrodes thereby covering the electrodes with more or less electrolytic solution. The increase or decrease of immersion in the electrolytic solution produces a corresponding change in impedance between the electrodes. This change in impedance is measured using an appropriate electrical circuit and is used to determine the change in tilt.
Tilt sensing devices, originally conceived for weapons delivery and aircraft navigation, have found a wide variety of uses. This is primarily because the tilt sensor's voltage signal output may provide an input to a preprogrammed guidance or other system, or provide an indication of the tilt angle via an electrical signal at a location remote from the sensor.
It is also generally known that existing tilt sensors, such as the electrolytic tilt sensor, may consist of a tubular or channeled glass envelope partially filled with an electrolytic fluid having conducting metal electrodes (working and common electrodes) formed therein. The envelope configuration, construction, type of electrolyte, electrode arrangement and number of electrodes may be varied to provide the desired operating characteristics. However, it is also known that many of such existing tilt sensors produce less than accurate results and/or suffer from stability problems caused by, for example, reactions between the electrolytic fluid and the electrodes.
U.S. Pat. No. 5,581,034 to Dao et al. (Dao '034) and U.S. Pat. No. 3,241,374 to Menkis (Menkis '374) attempt to solve some of the problems associated with the use of electrolytic fluid by taking advantage of the convective properties of a heated gas.
Referring now to
FIG. 2
, there is shown a schematic diagram of a tilt sensor
200
according to Dao '034 which utilizes the properties associated with convective gas currents. Dao '034 discloses a convective accelerometer and inclinometer having two temperature sensing elements mounted within a sealed enclosure containing a gas. The application of heat to the gas within the enclosure by a heating element causes the gas to flow in a predetermined pattern in free convection. The less dense heated air rises and passes over sensing elements in the form of wires positioned throughout the enclosure. The resistance of a sensing element wire changes in proportion to the change in temperature, i.e. how much heated air passes over it. How much heated air passes over a sensing element is a function of tilt; thus, the resistive temperature coefficient change allows the tilt angle measurements to be performed with a corresponding electrical circuit. Convective accelerometer
200
is comprised of a sealed container
205
, a first temperature sensing element
210
, a second temperature sensing element
220
, and a heating element
230
. Heating element
230
heats a gas enclosed within sealed container
205
and the resistive temperature coefficient of the first and second temperature sensing elements
210
and
220
change in proportion to the amount of heat transferred from the heated gas. As noted, since heated air rises, the temperature sensing elements will receive more or less heat depending on whether they are rotated to a position that is partially above or partially below heating element
230
. The change in the resistive temperature coefficient of the first and second temperature sensing elements
210
and
220
is measured and used to determine a corresponding tilt angle.
Referring now to
FIG. 3
, there is shown a schematic diagram of a device for sensing acceleration
300
according to Menkis '374. Menkis '374 discloses a device for sensing acceleration which is comprised of a heater located between at least two thermistors within a cylinder. When the cylinder is displaced, more or less heated gas passes over the thermistors located at the ends of the cylinder. The corresponding change in resistance of the thermistors is sensed by an appropriate electrical circuit and an output voltage is correlated to a tilt angle or acceleration.
The Menkis '374 device
300
is comprised of a sealed enclosure
310
having an elongated tubular member
320
disposed therein. A heater
330
is located midway within elongated tubular member
320
. Elongated tubular member
320
has two openings located at either end. Within each opening is disposed a bead thermistor
340
,
340
a
for sensing heat. When device
300
moves in the direction of travel
350
, heat flows in the tube as a function of acceleration of the tube. More heat will be directed to bead thermistor
340
a
and less heat will be directed to bead thermistor
340
. The resistance of bead thermistors
340
,
340
a
change in proportion to the amount of heat received. Thus, the amount of acceleration can be determined based upon the amount of heat received at each bead thermistor
340
,
340
a
as measured by the corresponding change in resistance. An appropriate electrical circuit connected to bead thermistors
340
,
340
a
measure the change in resistance and determine the amount of acceleration. Unfortunately, bead thermistors
340
,
340
a
also have a resistive temperature coefficient property that may vary widely and are affected by external temperature sources. The resistive temperature coefficient is a factor in producing inaccurate results. Therefore, there is a need in the art for a tilt sensor device which minimizes the reliance on temperature coefficient properties.
While some of the problems associated with electrolytic tilt sensors may be solved using a gas-based tilt sensor, such as Menkis '374 and Dao '034, the reliance on the resistive temperature coefficient of sensor wires in determining a tilt angle brings with it its own associated drawbacks. For example, sensor wires are more sensitive to changes in outside temperatures not associated with a change in angle or inclination. In addition, the sensor elements are constructed of very thin wire and frequently break. Also, the need for precisely balanced placement of the sensor wires, the need to measure angular movements of the housing, the need for reliable performance in various operating environments, and other factors
Dilworth & Barrese LLP
Fulton Christopher W.
The Fredericks Company
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