CAPACITIVE DETECTOR DEVICE

• US 3,826,979 A
• Filed: 06/18/1973
• Issued: 07/30/1974
• Est. Priority Date: 08/10/1972
• Status: Expired due to Term

• Current Assignee: Helmut Steinmann
• Original Assignee: Helmut Steinmann
• Inventors: Steinmann, Helmut
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/370,963
• Time in Patent Office: 407 Days
• Field of Search: 324/61P,61R 200/61.05,61.04 15/150.12,25C 318/483,443
• US Class Current: 361/178
• CPC Class Codes: B60S 1/0822 characterized by the arrangement or type of detection means
• CPC Class Codes: B60S 1/0829 Oscillator-resonator rain sensor
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: G01N 27/225 by using hygroscopic materials
• CPC Class Codes: G01R 27/2635 Sample holders, electrodes or excitation arrangements, e.g. sensors or measuring cells
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Abstract

A stray field capacitor with three plates edge to edge in a row has its center plate grounded, and normally most of the stray field of a signal applied to one of the end plates is between that end plate and the center plate which shields the other end plate. A reverse phase signal of proper amplitude may be used to reduce to zero the quiescent output of a receiver attached to the other end plate of the capacitor. If the capacitor plates are mounted on the inside of the windshield of a motor vehicle, the receiver will switch on the windshield wipers when moisture collects on the windshield.

Claims

1. A capacitive detector device comprising:

a stray field capacitor (1) having three electrodes disposed edge to edge in adjacent sequence on a continuous surface of no great curvature, said electrodes being thin in the direction perpendicular to said surface, the middle electrode (3) being connected to a steady reference potential and thereby serving to shield one end electrode from the other;

signal generating means (5) connected to a first end electrode (2) of said three electrodes, and signal receiving means (6) connected to the second end electrode (4) for detecting increased transmission from said signal generating means (5) as the result of changes in the configuration of the electric field in the neighborhood of said capacitor, said second electrode having a dimension in the direction of sequence of said electrodes which is large compared to the spacing between adjacent electrodes.

2. A capacitive detector device as defined in claim 1, in which said surface is a plane surface.

3. A capacitive detector device as defined in claim 1, in which said first end electrode (2) has the form of a narrow strip electrode with its narrow dimension being the dimension more nearly aligned with the direction of sequence of said electrodes.

4. A capacitive detector device as defined in claim 1, in which said signal generatiNg means generates low frequency sinusoidal electric waves.

5. A capacitive detector device as defined in claim 4, in which said signal receiving means (6) is provided with a balancing means (7) in which a reverse phase signal from said signal generating means is applied to said balancing means (7) at such an amplitude as to balance out and cancel the signal received by said receiving means (6) through the field of said capacitor during normal conditions, so that said balancing means (7) will provide a signal only during abnormal conditions which it is desired to detect.

6. A capacitive detector device as defined in claim 1, in which said electrodes are mounted near the exterior surface of a motor vehicle and the output of said receiver is used to activate or disable a windshield wiper, according to the presence or absence of moisture on an outer surface of said motor vehicle.

7. A capacitive detector device as defined in claim 6, in which said electrodes are disposed on the inner surface of the windshield of said motor vehicle.

8. A capacitive detector device as defined in claim 6, in which said electrodes are mounted at a position on the inner surface of the windshield of a motor vehicle opposite a portion of the surface of the windshield of said motor vehicle which is swept by windshield wipers.