Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-08-03
2001-06-19
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S664000
Reexamination Certificate
active
06249130
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a capacitive sensor for measuring material properties such as moisture or for detecting the presence or proximity of an object.
Most capacitive sensors for measuring material properties use a parallel plate or concentric cylinder design. The sensors work well in the laboratory or in a continuous stream of material, but certain applications require a less obtrusive sensor. Proximity sensors may be used to measure the dielectric properties of an object without entering or penetrating the object.
Proximity detectors typically measure capacitance between one conductor and ground and detect the presence of an object by noting the change in sensor capacitance when the object comes within the electric field generated between the sensor and a. reference potential. To measure in only one direction, such a sensor will typically be shielded on one side with a reference potential. This prevents observing objects on the shielded side but introduces a large measured capacitance which diminishes the sensitivity of the sensor.
BRIEF DESCRIPTION OF THE PRIOR ART
Attempts have been made to develop a capacitive sensor having a field which extends in one direction without diminishing sensitivity. The Vranish, et al., U.S. Pat. No. 5,166,679, for example, discloses a capacitive proximity sensing element which is backed by a reflector driver at the same voltage as the sensor. This results in an effective shield that does not increase the measured capacitance. However, complex circuitry is required to drive the shield.
The present invention was developed in order to overcome the drawbacks of the prior devices by providing a directional capacitive sensor with a high degree of sensitivity which does not require complicated circuitry to drive a shield.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the invention to provide a capacitive sensor element including a dielectric substrate having a planar configuration, a pair of sensing electrodes arranged in spaced relation on one surface of the substrate, and shield electrodes arranged on the substrate. A first shield electrode is arranged on the opposite surface of the substrate from the sensing electrodes and parallel thereto. The first shield electrode interrupts and thus limits the measuring field defined by the electric field lines generated from one of the sensing electrodes when an electric current is supplied thereto. A second shield electrode is arranged on the same surface of the substrate as the sensing electrodes in co-planar relation. This shield electrode prevents the dense electric field very near the sensor element from severely dominating the capacitive measurement.
According to a more specific embodiment of the invention, the first and second shield electrodes are connected with a reference potential and the sensing electrodes are formed of a copper film.
According to a further object of the invention, the capacitive sensing element is incorporated into a shunt-mode capacitive sensing circuit including an operational amplifier. One of the sensing electrodes is connected with an input of the operational amplifier and a voltage source is connected with the other sensing electrode. A reference capacitor is connected across the operational amplifier between the one input and the output thereof.
REFERENCES:
patent: 3694742 (1972-09-01), Bergmanis
patent: 4099118 (1978-07-01), Franklin et al.
patent: 5166679 (1992-11-01), Vranish et al.
patent: 5363051 (1994-11-01), Jenstrom et al.
patent: 5402075 (1995-03-01), Lu et al.
patent: 5436565 (1995-07-01), Gammell
patent: 5546006 (1996-08-01), Louge
patent: 5585732 (1996-12-01), Steele et al.
patent: 5682788 (1997-11-01), Netzer
J.R. Smith, Field Mice: Extracting hand geometry from electric field measurements, IBM Systems Journal, vol. 35, Nos. 3 & 4, 1996, pp 587-608, May 31, 1996.
AgriChem, Inc.
Gutenkauf Robert W.
Metjahic Safet
Nguyen Vincent Q.
LandOfFree
Shielded flat-plate proximity/dielectric properties sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Shielded flat-plate proximity/dielectric properties sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Shielded flat-plate proximity/dielectric properties sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2488667