Proximity detection system and oscillator, and method of using same

• US 5,463,378 A
• Filed: 12/14/1993
• Issued: 10/31/1995
• Est. Priority Date: 01/02/1990
• Status: Expired due to Term

• Current Assignee: Seewater, Inc.
• Original Assignee: Raptor, Inc.
• Inventors: Gibb, Robert F.
• Primary Examiner(s): Swarthout, Brent
• Assistant Examiner(s): Lefkowitz, Edward
• Application Number:
  US08/167,568
• Time in Patent Office: 686 Days
• Field of Search: 340/612, 340/618, 340/620, 73/304 C, 73/304 R, 73/290 R, 73/302, 331/64, 331/65, 324/660, 324/674, 324/681
• US Class Current: 340/618
• CPC Class Codes: F04B 2205/50 Presence of foreign matter in the fluid
• CPC Class Codes: F04B 23/021 the pump being immersed in the reservoir
• CPC Class Codes: F04B 49/06 Control using electricity regulating by means of floats actuating electric switches F04B49/04
• CPC Class Codes: G01F 23/265 for discrete levels
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G05D 9/12 characterised by the use of electric means
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/96 Touch switches specially adapted for electronic time-pieces with no moving parts G04G21/08

Abstract

A proximity detection system includes a dual mode oscillator for generating a pair of ON and OFF control signals. A sensing circuit including a capacitance device detects the presence of a conductive object, such as a liquid, to cause the oscillator to switch its modes of oscillation.

Claims

1. A method of controlling an electrical load, comprising the steps of:

(a) providing a conductive medium;

(b) disposing a sensing means in proximity with said conductive medium, said sensing means possessing a capacitance which varies from a very low capacitance value when said sensing means is in a first proximity to said conductive medium and changing to a substantially higher capacitance value when in a second proximity to said conductive medium;

(c) providing a dual mode oscillator having an input connected to said sensing means, said dual mode oscillator having an output for providing a control signal to said electrical load and functioning, in a first mode as a phase shift oscillator to generate said control signal at a first duty cycle, and in a second mode as an RC oscillator to generate said control signal at a second duty cycle;

(d) generating a control signal, at the output of said dual mode oscillator, having a first duty cycle determined by a first capacitance value of said sensing means, to thereby control said electrical load according to the first duty cycle of said control signal;

(e) varying the capacitance of said sensing means from said first capacitance value to a second capacitance value; and

(f) changing the duty cycle of said control signal from said first duty cycle to said second duty cycle in response to a change in the capacitance of said sensing means from said first capacitance value to said second capacitance value, to thereby control said electrical load according to said second duty cycle of said control signal.

2. In a system having a capacitive sensor disposed in proximity to a conductive medium, a method of activating and deactivating an electrical load, comprising the steps of:

(a) providing a dual mode oscillator having an input connected to said capacitive sensor and an output connected to said electrical load, said dual mode oscillator generating, at the output thereof, a control signal having a variable duty cycle for activating and deactivating said electrical load;

(b) changing the capacitance of said capacitive sensor by changing the proximity of said capacitive sensor with respect to said conductive medium; and

(c) in response to the changing in the capacitance of said capacitive sensor, changing the operation of said dual mode oscillator from a first type of oscillator to a second type, and thereby change the duty cycle of said control signal from a first duty cycle to a second duty cycle to activate and deactivate said electrical load according to the duty cycle of said control signal.