Proximity detection system and oscillator

• US 5,287,086 A
• Filed: 09/23/1991
• Issued: 02/15/1994
• 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): HOFSASS, JEFFERY A
• Application Number:
  US07/763,990
• Time in Patent Office: 876 Days
• Field of Search: 340/618, 340/620, 340/612, 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 system, operating in proximity to a conductive medium, for controlling an electrical device, comprising:

sensing means, having a variable capacitance, the capacitance of said sensing means having a very low capacitance value when 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; and

a dual mode oscillator, having an output providing an output control signal to said electrical device and being responsive to a change in the capacitance value of said sensing means, for switching from a first mode of operation, as a phase shift oscillator having a first duty cycle, to a second mode of operation, as an RC oscillator having a second duty cycle, to thereby control the operation of said electrical device in accordance with said first and second duty cycles of said output control signal.

2. A system according to claim 1 further including encapsulating means for electrically insulating said dual mode oscillator and said sensing means from said conductive medium.

3. A system according to claim 1 further comprising comparator means, including switch means, responsive to said output control signal changing between said first and second duty cycles, for activating and de-activating said electrical device.

4. A system according to claim 3, wherein said comparator means includes a low pass filter for generating a time delay when said output control signal changes between said first and second duty cycles and extracting a DC component from said output control signal to cause said comparator means to effect the generation of a final control signal for activating and de-activating said electrical device according to said first and second duty cycles of said output control signal.

5. A system according to claim 1, wherein said dual mode oscillator includes an operational amplifier having an output terminal serving as the output of said dual mode oscillator, said operational amplifier having an inverting input, connected to said sensing means, and a noninverting input, connected to a source of reference potential, a first feedback resistor connected between the output terminal and the noninverting input of said operational amplifier and a second feedback resistor and a feedback capacitor connected in parallel between the inverting input and the output terminal of said operational amplifier, the value of said feedback capacitor being sufficiently larger than the capacitance value of said sensing means, when said sensing means is in either a one of said first proximity and said second proximity to said conductive medium, to enable said dual mode oscillator to function as a phase shift oscillator, and the capacitance value of said sensing means being much larger than the capacitance value of said feedback capacitor, when said sensing means is in the other proximity of said first proximity and said second proximity, to thereby render said feedback capacitor ineffective to thus enable said dual mode oscillator to function as an RC oscillator by feeding back, through said second feedback resistor, at least a portion of the output control signal from the output terminal to the inverting input of said operational amplifier.

6. A system operating in proximity to a conductive medium, for controlling the operation of an electrical load, comprising:

(a) capacitive sensing means disposed in proximity with said conductive medium and possessing a capacitance which varies in accordance with the proximity of said conductive medium with respect to said sensing means;

(b) a dual mode oscillator having an input connected to said sensing means, said oscillator being controlled, at the input thereof, by the capacitance of said sensing means and generating a pulsating signal having a first duty cycle when said sensing means is disposed in a first proximity relative to said conductive medium, and generating said pulsating signal at a second duty cycle when said sensing means id disposed in a second proximity relative to said conductive medium; and

(c) means, connected between the output of said dual mode oscillator and said electrical load, for extracting a DC component from said pulsating signal during each of said first and second duty cycles and providing a DC control signal having a magnitude proportional to said DC component to said electrical load to control the operation thereof.

7. The system according to claim 6, further including means for electrically insulating said capacitive sensing means and said oscillator from said conductive medium.

8. The system according to claim 6, wherein the means for extracting said DC component and providing said DC control signal to said electrical load comprises a filter and comparator, responsive to the DC component in each of the first and second duty cycles of said pulsating signal, to thereby provide a final control signal to said electrical load which varies in magnitude according to the magnitude of the DC component in each of the first and second duty cycles of said pulsating signal.

9. The system according to claim 6, further including a feedback resistor and feedback capacitor connected in parallel from the output to the input of the oscillator.

10. A control system, adapted for disposition in the proximity of a conductive medium, for controlling the operation of an electrical load, comprising:

(a) capacitor sensing means having a conductor encapsulated in a nonconductive material and being disposed in proximity with said conductive medium, said conductor serving as one plate of a capacitor and said conductive medium serving as the other plate of said capacitor, whereby said capacitor sensing means possesses a capacitance which varies in accordance with the proximity of said conductive medium with respect to said capacitive sensing means; and

(b) a dual mode oscillator having an input connected to said conductor in said sensing means and an output, including means for transferring a control signal to said electrical load, said oscillator further including feedback means for feeding back at least a portion of said control signal from the output to the input thereof and being controlled, at the input thereof, in a first instance, by the portion of the control signal from said feedback means to effect the generation of said control signal at a first duty cycle, when said sensing means id disposed in a first proximity relative to said conductive medium, and being controlled, in a second instance, by the capacitance of said sensing means and a further portion of the control signal from said feedback means to effect a further generation of said control signal at a second duty cycle, when said sensing means is disposed in a second proximity relative to said conductive medium, to thereby control the operation of said electrical load according to the first and second duty cycles of said control signal.

11. A system for operating a motor driven pump to control the level of a conductive fluid in a vessel, comprising:

(a) a capacitive sensor having a conductor encapsulated in a nonconductive material and being disposed in a prescribed proximity relative to said conductive fluid for sensing the level of said conductive fluid in said vessel, said conductor serving as one plate of a capacitor and said conductive fluid serving as the other plate of said capacitor, whereby the capacitance of said capacitive sensor varies in accordance with the level of said conductive fluid in the proximity of said capacitive sensor,

(b) a dual mode oscillator having an input connected to said conductor in said capacitive sensor and being controllable by the capacitance thereof to operate in a first mode as a phase shift oscillator when said conductive fluid is at a first level and to operate in a second mode as an RC oscillator when said conductive fluid is at a second level, said oscillator generating a pulsed output signal having a first duty cycle when in said first mode and having a second duty cycle when in said second mode, said pulsed output signal possessing a first DC component associated with said first duty cycle and a second DC component associated with said second duty cycle;

(c) a comparator for providing a control signal to said pump; and

(d) a filter connected between the output of said oscillator and an input to said comparator, said filter extracting the DC component from said pulsed output signal during each of said first and second modes to provide a DC signal to said comparator to effect, at the output thereof, a control signal having a magnitude effective to turn said pump on and off according to the level of liquid in said vessel.

12. A system, operating in proximity to a conductive medium, for controlling the operation of an electrical load, comprising:

(a) a capacitive sensor disposed in proximity with said conductive medium and possessing a capacitance which varies from a very low value to a substantially higher value in accordance with the proximity of said conductive medium with respect to said sensor;

(b) a dual mode oscillator capable of operating in a first mode as a phase shift oscillator and operating in a second mode as an RC oscillator, said oscillator having an input connected to said sensor, and an output for generating a pulsating signal having a different duty cycle in each of said first and second modes, a feedback capacitor and a feedback resistor connected in parallel between the input and the output of said oscillator, said feedback capacitor normally providing a feedback signal to enable said oscillator to operate in said first mode, to generate a pulsating signal having a first duty cycle having a first DC component, when the capacitance of said sensor is significantly less than the capacitance of said feedback capacitor, said oscillator switching to said second mode to generate a pulsating signal having a second duty cycle having a second DC component when the capacitance of said sensor exceeds the capacitance of said feedback capacitor, such exceeding rendering said feedback capacitor substantially ineffective, to thus enable the feedback resistor to form an RC time constant in conjunction with the capacitance of said sensor to thereby switch said oscillator from said first mode to said second mode; and

(c) means, connected to the output of said oscillator and responsive to the pulsating signal therefrom, for providing a control signal for controlling the operation of said electrical load in accordance with the DC component in each of said first and second duty cycles of said pulsating signal.