Capacitor detector device

• US 3,973,208 A
• Filed: 02/14/1975
• Issued: 08/03/1976
• Est. Priority Date: 02/14/1975
• Status: Expired due to Term

• Current Assignee: UT Medical Manufacturing Incorporated
• Original Assignee: Dovey Manufacturing Company
• Inventors: Diamond, Donald A.
• Primary Examiner(s): Heyman, John S.
• Application Number:
  US05/550,111
• Time in Patent Office: 536 Days
• Field of Search: 328/5, 331/65, 340/258 B
• US Class Current: 307/652
• CPC Class Codes: G01V 3/088 operating with electric fields G01V3/082 takes precedence
• CPC Class Codes: G08B 13/26 by proximity of an intruder causing variation in capacitance or inductance of a circuit

Abstract

A capacitor detector device for detecting a change of capacitance in a protected zone, which device comprises an antenna element adapted to be mounted in spaced relationship with a grounded element to define the protected zone between the elements and having a nominal capacitance therebetween, which capacitance is changed upon intrusion of an object to be detected. The device includes an oscillator means for pumping, at a preselected frequency, the grounded element with respect to an internal floating ground of the device, means for connecting the antenna to the floating ground of the device whereby the antenna is capacitively coupled to the pumped ground element and means for detecting changes in the capacitive coupling of selected amounts between the antenna element and the pumped grounded element.

Claims

1. A capacitor detector device for detecting the change of capacitance in a protected zone, said device comprising:

an antenna element adapted to be mounted in spaced relationship with a grounded element to define said protected zone between said elements and having a nominal capacitance therebetween which capacitance is changed upon intrusion of an object to be detected;

an oscillator means independent of said antenna element for pumping at a preselected frequency said grounded element with respect to an internal floating ground of said device;

means for connecting said antenna to said floating ground of said device whereby said antenna is capacitively coupled to said pumped grounded elements; and

means for detecting changes in the capacitive coupling of selected amounts between said antenna element and said pumped grounded element.

2. A capacitor detector device for detecting the change of capacitance in a protected zone, said device comprising:

an antenna element adapted to be mounted in spaced relationship with a grounded element to define said protected zone between said elements and having a nominal capacitance therebetween which capacitance is changed upon intrusion of an object to be detected;

an oscillator means for pumping at a preselected frequency said grounded element with respect to an internal floating ground of said device;

means for connecting said antenna to said floating ground of said device whereby said antenna is capacitively coupled to said pumped grounded elements; and

means for detecting changes in the capacitive coupling of selected amounts between said antenna element and said pumped grounded element, said change detecting device includes an operational amplifier having first and second inputs;

means for creating a control signal between said pumped grounded element and said antenna;

means for directing said control signal to said first input and means for creating a reference signal at said second input.

3. A capacitor detector device as defined in claim 2 including means for creating a null signal having said preselected frequency and a selected amplitude generally corresponding to the amplitude of said control signal when said nominal capacitance exists in said protected zone;

and means for directing said null signal to said second input.

4. A capacitor detector device as defined in claim 3 including means for adjusting said selected amplitude.

5. A capacitor detector device as defined in claim 2 including means for creating a null signal having said preselected frequency and generally in phase with said control signal;

and, means for directing said null signal to said second input.

6. A capacitor detector device for detecting the change of capacitance in a protected zone, said device comprising:

an antenna element adapted to be mounted in spaced relationship with a grounded element to define said protected zone between said elements and having a nominal capacitance therebetween which capacitance is changed upon intrusion of an object to be detected;

an oscillator means independent of said antenna element and connected to said grounded element for creating a first operating signal alternating with respect to said grounded element at a preselected frequency;

a voltage control device for maintaining a selected voltage between said first operating signal and an internal instrument ground whereby said instrument ground is a second operating signal which alternates with said first operating signal and is displaced therefrom by said selected voltage;

means for subjecting said antenna to one of said operating signals;

means for creating a control signal on said antenna at said preselected frequency and by the voltage relationship between said one of said operating signals and said grounded element; and

means for detecting changes of a selected amount in the magnitude of said control signal.

7. A capacitor detector device for detecting the change of capacitance in a protected zone, said device comprising:

an antenna element adapted to be mounted in spaced relationship with a grounded element to define said protected zone between said elements and having a nominal capacitance therebetween which capacitance is changed upon intrusion of an object to be detected;

an oscillator means connected to said grounded element for creating a first operating signal alternating with respect to said grounded element at a preselected frequency;

a voltage control device for maintaining a selected voltage between said first operating signal and an internal instrument ground whereby said instrument ground is a second operating signal which alternates with said first operating signal and is displaced therefrom by said selected voltage;

means for subjecting said antenna to one of said operating signals;

means for creating a control signal on said antenna at said preselected frequency and by the voltage relationship between said one of said operating signals and said grounded element; and

means for detecting changes of a selected amount in the magnitude of said control signal, said change detecting means including an operational amplifier having first and second inputs;

means for directing said control signal into said first inputs and means for creating a reference signal at said second input.

8. A capacitor detector device as defined in claim 7 including means for creating a null signal having said preselected frequency and a selected amplitude generally corresponding to the amplitude of said control signal when said nominal capacitance exists in said protected zone;

and means for directing said null signal to said second input.

9. A capacitor detector device as defined in claim 8 wherein said operational amplifier is a Norton current responsive operational amplifier with said first input being the inverted input and the second input being the non-inverted input.

10. A capacitor detector device as defined in claim 9 wherein one of said operating signals is applied to said second input.

11. A capacitor detector device as defined in claim 8 including means for adjusting said selected amplitude.