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Publication numberUS3103655 A
Publication typeGrant
Publication dateSep 10, 1963
Filing dateAug 14, 1962
Priority dateAug 14, 1962
Publication numberUS 3103655 A, US 3103655A, US-A-3103655, US3103655 A, US3103655A
InventorsJones Clarence S
Original AssigneeJones Clarence S
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Proximity responsive switching system
US 3103655 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Sept. 10, 1963 c. s. JONES PROXIMITY RESPONSIVE SWITCHING SYSTEM 2 Sheets-Sheet 2 Filed Aug. 14, 1962 U @O LP m6 23 2;? Wm R Jo CLARENCE 8. c/OA/ES INVENTOR.

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United States Patent ()1 3,103,655 PROXIMITY RESPONSIVE SWITCHING SYSTEM Clarence S. Jones, 991 S. Springer Road, Los Altos, Calif. Filed Aug. 14, 1962, Ser. No. 216,887 11 Claims. (Cl. 340-458) This invention relates to switching systems in general, and in particular to a condition responsive switching system which operates in response to a change of proximity of selected objects including persons.

There are many applications where it is desired to detect the presence or the absence of a particular object (condition) so that a desired response to the condition may be had. For example, one device used by the prior art to detect such a condition is the photoelectric beam which upon being interrupted by either a person or an opaque object provides an output signal indicative of the beam condition. Heretofore, many stores have made use of such photoelectric devices to control doors and escalators and the like for the convenience of their customers.

Also such photoelectric devices have found application in the automatic opening of garage doors when the beam across a driveway is interrupted by an approaching car. The problem encountered with such control devices is that they are non-selective and operate indiscriminately in response to any opaque object being interposed in the beam. Children running in the driveway and ice forming over the photoelectric cell during freezing weather are but a few examples of unwanted or undesired actuation of a photoelectrically controlled garage door.

Another condition responsive device which has been used heretofore is the pressure actuated switch which operates in response to the condition depressing the switch. One application of such pressure responsive switches is in the control of trafiic lights positioned between, for example, a major and a minor trafiic artery. The trafiic light normally permits trafiic flow along the main artery and changes only in response to vehicles approaching the intersection along the minor artery to permit maximum flow along the main artery.

Such pressure responsive switches are usually imbedded in the pavement Where they extend over a substantial portion of the width of the right side of the minor arteries. As cars pass over such a switch they depress the same thereby providing an indication of their presence which is utilized to change the trafiic signal. Such switches are mechanical in nature and are capable of much greater selectivity than photoelectric devices in that the actuating pressure can be set sufiiciently high so that only cars can actuate the same. However, such switches require frequent maintenance, are expensive to install and have been found to be unreliable. Additionally, such switches require a resilient cover which forms a portion of the roadway and which is subject to the same wear and tear as the road surface and consequently must he often replaced at great cost and inconvenience.

In rolling mills, and other industrially controlled processes involving the continuous flow of material over a fixed path, it is often desirable to stop the process when there is an interruption of flow due to breakage. Such breakage is usually accompanied by a change of proximity of the material flowing and a certain point in the flow bed which is translatable for operation of switches. Heretofore such controls have utilized expensive and unselective mechanical or photoelectric devices to detect :a change in proximity.

Another area of application of proximity switches is in the protection of property, particularly in isolated areas, which heretofore required extensive patrolling. Photoelectric devices are too unselective since they are easily set off by stray animals or even by wind blown objects such as paper. P atrolling is an expensive means of safeguarding isolated areas and not always reliable.

In all the above outlined applications of proximity responsive switching system, the common element is proximity of an object or person, each type of which has certain electrical or magnetic characteristics which differ from object to object or from object to person. For example, a car is a ferromagnetic substance and a person is a dielectric substance. Also the effect of a car in a magnetic circuit is different from that of a moving steel bar.

It is therefore a primary object of this invention to provide a switching system which is responsive to either the presence or the absence of a condition.

It is a further object of this invention to provide a switching system capable of changing its switching state in response to a change of proximity of a selected object or a person.

It is another object of this invention to provide a switching system for selectively actuating a traffic control system in response to cars passing over selected sections of roadway.

It is still another object of this invention to provide a switching system for controlling industrial processes in which the switching system actuates either an alarm or a remedial means upon the occurrence of certain proximity changes.

It is still another object of this invention to provide a reliable, economical and inexpensive switching system which responds to a change of proximity of an object or person in a selected vicinity and which provides an output signal which is utilized to operate devices in response to the change of conditions actuating the switching system.

It is still a further object of this invention to provide a switching system which is operative to change its state upon the change of proximity of selected objects and which utilizes either the electric or magnetic properties of the selected object to change the resonant frequency of a tuned circuit and which is reliable, inexpensive and selective.

The preferred embodiment of this invention includes an oscillator which changes its output frequency in response to the happening of a condition, that is in response to a change in the proximity of a magnetic or electric (dielectric) object. The condition operates upon the tank circuit of the oscillator and changes the resonant frequency thereof. The oscillator output signal is then applied to a frequency sensitive phase inverter which provides a degree phase shift only at a selected frequency usually indicative of the normal condition. In the abnormal condition, the phase shifter shifts the phase either less or more than 180 degrees.

The phase inverter (shifted) output signal and the oscillator output signal are then applied to rectifiers and after being rectified are applied to a circuit which provides an output signal only when the two rectified signals are not exactly 180 degrees out of phase, a condition which occurs only when the oscillator is detuned by the abnormal condition. The circuit output signal is then utilized either to activate a relay or some other utilization means to indicate or take corrective action in response to the happening of the abnormal conditions.

Other objects and a better understanding of the invention may be had by reference to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of the proximity responsive switching system of this invention;

FIG. 2 is a schematic circuit diagram of the proximity responsive switching system of FIG. 1

FIGS. 3A to 3G are waveform diagrams useful in explaining the operation of the proximity response switching system of this invention in the presence of the normal condition; and

FIGS. 4A to 4G are waveforms, such as the ones shown in FIGS. 3A to 3G in the presence of the abnormal condition.

Referring now to the drawings, and particularly to- FIG. 1 thereof, there is shown an embodiment of the proximity responsive switching system of this invention and generally designated by reference character 10. Switching system comprises a signal generator or oscillator 12 which includes a tank circuit generally indicated by reference character 13 having inductive impedance 1-4 and capacitive impedance 15. Oscillator. 12 may be of standard configuration except that tank circuit 13- is so constructed that its resonance frequency changes with change of proximity of a selected object such as, for example, a car. Oscillator 13 provides an output signal 16 on lead 16' whose frequency is the same or very close to the resonant frequency of tank circuit 13.

Oscillator output signal 16 is applied to a frequency sensitive phase shift means 17 which provides a 180 degree phase shift at a preselected frequency thereby operating as a phase inverter 16. At all other frequencies, the phase shift introduced by means 17 is either larger or smaller than 180 degrees. Means '17 may comprise a conventional phase inverter having a tank circuit, such as 18, connected between the output lead 19 and a reference point. Tank circuit 18 has the same electrical characteristics as tank circuit 13 when the latter is in its normal position, i.e., the same resonant frequency. Other conventional frequency sensitive phase inverter means may be employed, the major requirement being to provide a 180 degree phase shift to oscillator output signal 16 at the normal condition and a phase shift different from 180 degrees when oscillator output signal 16 reflects an abnormal condition. Phase shift means 17 provides a phase shifted output signal 19 on lead 19'.

Phase shifted output signal 19 and oscillator output signal 16 are then respectively applied to a pair of substantially similar rectifying means 20 and 21 which, ,in the particular embodiment illustrated, cut olf the positive .portions of alternating current signals 16 and 19 to provide rectified output signals 22 and 23. Rectified output signals 22 and 23 are applied to a circuit 24 .which performs the logical function usually associated with a logical NOR circuit or a logical AND circuit. In other words, circuit 24 is responsive to both signals 22 and 23 and provides a circuit output signal only when both signals are either instantaneously zero or instantaneously negative. The output signal provided by circuit .24. is also referred to as control signal 25.

Control signal 25 is applied to a conventional filter and amplifier circuit 26 which filters and amplifies .control -signal 25 .to provide, in the embodiment shown, a negative DC. output or switching signal 27 whose amplitude proportionally reflects the amount of energy passed by circuit 24. Amplifier 26 may also include a driver to provide a switching signal 27 of suflicient output power to drive a suitable utilization device 28. Utilization device 28 may be a' relay coil or an alarm bell or some other devicecapable of operating a selected means to indicate abnormal condition.

Oscillator 12, and particularly tank circuit 13, is so constructed that the proximity of a selected type of object changes its resonant frequency and thereby the frequency of oscillator output signal 16. For example, when switching system 10 is to be employed in connection with a traffic system, inductive impedance 14 may take the form of a large loop embedded in the road surface. When a car passes over the embedded loop, it changes the magnetic flux path and thereby the inductive impedance of theloop. As a consequence, the resonant frequency of the tank circuit changes. Since, for this type of application of switching system 10, a switching signal is desired when a car passes over the embedded loop, 'the presence of the car is the abnormal conditon. Ac-

cordingly, phase shift means 17 is so constructed to provide a degree phase shift in the absence of a car.

Switching system 10 maylalso be conditioned to respond to non-metallic objects such as liquids or persons. For example, the change of liquid level may be signalled by utilizing a large capacitive structure for capacitive impedance 15, so placed that the liquid forms a dielectric through which the electric field passes. As the liquid level rises, more and more of the areas of the capacitive impedance is exposed to a liquid dielectric which thereby causes a change of the resonant frequency of tank circuit 13. The same principle may be used with humans, i.e., the dielectric properties of the human body may be utilized to change the capacitive impedance of tank circuit 13 to indicate human presence by a change in frequency.

In case of controlling rolling mills or similar endless motion of materials, the normal condition would involve the presence of the material and the abnormal condition the absence thereof due to breakage. If the material is ferromagnetic, then it may be used to change the inductance of coil 14 and if the material is primarily dielectric in nature it may be used to change the capacitance impedance 15 of circuit 13. Many other means of sens ing a change of condition will become immediately apparent to those skilled in the art. For example, the inductance may form a coil around the flowing material so that breakage has the same effect as withdrawal of a core.

In operation, as long as oscillator 12 is exposed to a normal condition, it generates an oscillator output signal 16 of such a frequency that frequency sensitive phase shifter 17 operates thereon to provide an output signal 19 which is exactly 180 degrees out of phase with oscillator output signal 16. Or conversely, the frequency sensitive elements in phase shifter 17 may be set to provide a 180 degree phase shift when signal 16 signifies a normal condition. After rectification of signals 22 and 23 they are exactly 180 degrees out of phase and NOR circuit 24 will always see one or the other of the rectified signals but not both simultaneously. Consequently, control signal 25 is zero and utilization .device 28 has no input power. Accordingly,'utilization device 28 is not actuated.

If an AND circuit is used instead of NOR circuit 24, the same 'result is obtained. Since an AND circuit only provides an output signal when both inputsignals 22 and 23 are simultaneously different from zero, then as long as they are exactly 180 degrees displaced with respect to one another, no control signal 25 is obtained.

As soon as oscillator 12 senses an abnormal condition,

the resonant frequency of tank circuit 13 changes and phase shift means 17, by virtue of tank circuit 18 (or some other frequency sensitive circuitry), provide a phase shift which is either greater or less than 180 degrees. If tank circuit 18 is utilized, its electrical characteristics are of course fixed, so that the abnormal condition will not effect the phase shift. Accordingly,- oscillator output signal 16 and phase shift output signal 19 will not be 180 degrees out of phase. Consequently, rectified output signals 22 and 23 are not exactly shifted by 180 degrees with respect to oneanother and the signals 22 and 23 will have zero voltage on both leads simultaneously (and of course negative voltages simultaneously) generating a control signal of the form indicated at 25. This is true whether circuit 24 is of the NOR or AND type.

After proper filtering and amplification of control signal 25 an output D.C. switching signal 27 is obtained having a magnitude reflecting the length of time rectified signals 22 and 23 are both Zero (or negative) and thereby the amount of phase shift produced. Utilizataion device 28, now being provided with a negative input signal 27, takes the desired action to indicate the exfixed and a phase shift means whose phase shift can be altered by the happening of a condition. In other words, instead of providing an oscillator tank circuit whose resonance frequency is changed by the abnormal condition, a fixed tank circuit is utilized and instead the tank circuit of phase shift means 17 is constructed to change its resonance frequency upon the occurrence of an abnormal condition. This is tantamount to an exchange of proximity responsive tank circuit 13 and fixed resonance tank circuit 18.

Referring now to FIG. 2 here is shown a specific embodiment of a proximity responsive switching system suitable for switching a trafiic light in response to the presence of a car. An emitter-controlled oscillator 40 comprising a transistor Q1 and Q2, resistors R1, R2, R3 and R4, and a tank circuit including impedances L1 and C1, provide an output signal (90 kilocycles per second) which is nearly equal in frequency to the resonance frequency of its tank circuit. Inductive impedance 1.1 may be a large coil embedding in the road pavement forming a permanent selected location for detecting a change of condition. Operating power is applied to oscillator 40 via leads 41 and 42 connected across a convenient power supply 43. The oscillator output signal is applied, via resistor R5, to a frequency sensitive phase inverter means 4 5 comprising transistor Q3, resistors R6, R7 and R3, and a fixed resonance tank circuit including impedances L2, C2 and C3.

The wave form of the oscillator output signal 16 is a simple sine wave as shown in FIG. 3A and the input signal to inverter means 45 is shown at FIG. 3B. Inverter means 45, as long as the tank circuit, including impedances C2, C3 and L2, has the same electrical characteristics as tank circuit including impedances L1 and C1, provides an output signal 19 on lead 46 which is a simple sine wave shifted in phase by 180 degrees with respect to oscillator signal 16 as shown in FIG. 3C.

Output signal 16 from lead 44- and output signal 19 on lead 46 are then respectively applied to drive a pair of emitter followers comprising transistors Q4 and Q5 and their respective emitter resistors R9 and R10. The output wave form transistors Q4 and Q5 are respectively shown in FIGS. 3D and 3E and comprise the rectified signals 22 and 23 (FIG. 1).

The emitter resistances R9 and R apply their output signal directly to a NOR circuit 47 via lead 48. This signal has a wave form as shown in FIG. 3F as long as the relative phase shift betwen signals 22 and 23 is exactly equal to 180 degrees. NOR circuit 47 is a base driven transistor Q6 which is biased by resistors R11, R12, and R13 so that it is always saturated. Resistor R12 is temeprature sensitive and provides proper bias at all operating temperatures. Accordingly, as long as the emitter followers do not simultaneously provide output signals, base driven transistor Q6 remains saturated. Consequently, there will be no, or substantially no, output signal as indicated in FIG. 3G.

When, however, inductive impedance L1 changes due to the presence of an automobile, the resonance frequency of the tank circuit and thereby the output frequency of oscillator 4-0 changes. Phase shifter means 45, because impedance L2 remains unaffected by the presence of the automobile, now provides a different phase shift resulting in a lack of negative output signal from the emitter follower Q4 and Q5. The output signals coresponding to the abnormal conditions are shown in FIGS. 4A to 4G which correspond to FIGS. 3A to 36 showing the normal condition.

The rectified signals shown in FIGS. 4D and 4F now are zero during a common time interval causing peaks to appear at output lead 48 which makes transistor Q6 momentarily non-conductive so that its output voltage will rise as best seen in FIGS. 4F and 4G. These output spikes are applied, via lead 49, to a filter inductor L3, across a filter capacitor C4 and a two staged amplifier in- 6 eluding transistors Q7 and Q8. Output lead 50 applies output power to relay coil K1.

There has been described a switching system which provides a switching signal in response to the detuning of a tank circuit by the occurrence of an abnormal condition. Detuning of the oscillator tank circuit is being accomplished by utilizing a physical characteristic of an object or person in changing the resonant frequency of a tank circuit. In the normal condition the resonant frequency of the tank circuit has one value and in the abnormal condition the resonant frequency of the tank circuit change to another value.

Even though this invention has been described with special reference to a trafiic signal control system in which the proximity of an automobile changes the resonant frequency, the same principle may be utilized with any object or person which or whose physical characteristic can be combined with the impedance of a tank circuit.

What is claimed is:

1. A proximity condition responsive switching system for providing a switching signal upon the occurrence of a proximity condition comprising:

(a) signal generator means for providing a signal whose frequency varies between a first frequency upon the occurrence of said condition and a second frequency upon the non-occurrence of said condition;

(b) frequency dependent phase shift means responsive to said signal and operative to provide a phase shift of substantially degrees to said signal when at said first frequency;

(c) unidirectional current conducting means for recti- :fying the signal from said genenator means and the signal from said phase shift means; and

(d) logical circuit means responsive to both the rectified signals and operative to provide said switching signal which is substantially proportional in amplitude to the difference in phase of both said signals from 180 degrees.

2. A proximity responsive switching system for providing a switching signal upon a selected object coming into close proximity therewith and comprising:

(a) signal generator means for providing a signal whose frequency is a function of the proximity of said selected object and which has a first frequency when said selected object is in close proximity;

(b) frequency dependent phase shift means responsive to said signal and operative to shift the phase of said signal, the phase shift being selected to be substantially equal to 180 degrees at the first frequency :and different from 180 for any other frequency;

(0) unidirectional current conducting means for rectifying the signal from said generator means and the signal from said phase shift means; and

(d) circuit means responsive to both the rectified signals and operative to provide said switching signal, said switching signal being substantially proportional to the difference in phase of both the rectified signals from 180 degrees.

3. A condition responsive switching system for providing a switching signal upon the occurrence of a proximity condition comprising:

(a) signal generator means responsive to said proximity condition and operative to provide an output signal having a frequency which varies between a first frequency upon the occurrence of said condition and a second frequency upon the non-occurrence of said condition;

(b) frequency dependent phase shift means responsive to said output signal and operative to shift the phase of said output signal by an amount substantially equal to 180 degrees at said first frequency and a different amount at any other frequency;

(0) means for rectifying said output signal and the phase shifted signal; and

(d) circuit means responsive to both rectified signals 7 and operative to derive an output signal unless only one of the rectified signals is zero.

4. A switching system in accordance with claim 3 in which said circuit means is an AND circuit.

5. A switching system in accordance with claim 3 in which said circuit means is a NOR circuit.

6. A proximity responsive switching system for providing a switching signal when a selected object approaches a selected proximity, said switching system comprising:

(a) signal generator means including a first tank circuit whose resonance frequency changes with a change of proximity of said selected objects, said signal generator means providing a generator signal of a first frequency when said selected object is outside said selected proximity; t

(b) phase shift means including a second tank circuit having a fixed resonance frequency, said phase shift means being frequency dependent and responsive to said generator signal and operative to shift the phase of said generator signal by 180 degrees at said first frequency;

(c) unidirectional current conducting means for rectifying said generator signal and the phase shifted signal; and

(d) logical circuit means responsive to both the rectified signals and operative to providesaid switching signal when the phase shift between said generator signal and the phase shifted signal is different from 180 degrees, the amplitude of said switching signal being proportional to the in-phase component of the rectified signals.

7. A proximity responsive switching system for providing a switching signal when a preselected object approaches a selected proximity, said switching system comprising:

(a) signal generator means including a first tank circuit whose resonance frequency changes with a change with a change of proximity of said preselected object, said signal generator means providing a generator signal of. a first frequency only when said selected object is at outside said selected proximity;

(b) frequency dependent phase shift means including a second tank circuit having a fixed resonance frequency, said phase shift means being responsive to said generator signal and operative to provide a phase shifted signal which is substantially out of phase with said generator signal only when at said first frequency;

() unidirectional current conducting means for rectifying said generator signal and the phase shifted signal; and w (d) logical circuit means responsive to both said rectified signals and operative to provide said switching signal when the phase shift between said generator signal and said phase shifted signal is not substantially equal to 180 degrees, the amplitude of said switching signal being proportional to their in-phase component.

8. A proximity responsive switching system for providing a switching signal when a selected object is Within a selected proximity range, said switching system comprising:

(a) signal generator means including a first tank circuit whose resonance frequency changes with proximity of said selected object, said signal generator means providing a generator signal of a first frequency when said selected object is outside said selected proximity range;

(b) frequency dependent phase shift means including a second tank circuit having a fixed resonance frequency, said phase shift means being responsive to said generator signal and operative to shift the phase of said generator signal by substantially 180 degrees at said first frequency only;

(c) rectifying means for rectifying said generator signal and the phase shifted signal;

(d) logical circuit means responsive to both the rec'- tified signals and conductive when both rectified signals are either simultaneously zero or simultaneously not zero; and

(e) filter and driver means for filtering and amplifying the signal conducted through said circuit means to derive said switching signal.

9. A condition responsive switching system for providing a switching signal upon the occurrence of a condition comprising: i

(a) signal generator means including a first tank circuit detunable upon the occurrence of a condition, said signal generator means providing a first signal having a frequency which follows the resonance frequency of said first tank circuit;

(b) frequency dependent phase shift means including a second tank circuit fixedly tuned to the frequency of said first tank circuit in the absence of the occurrence of said condition, said phase shift means being responsive to said first signal and operative to provide a second signal which is substantially degrees out of phase with said first signal when said first signal has a frequency representative of the absence of the occurrence of said condition;

(c) unidirectional current conducting means for rectifying said first and said second signals; and

(d) circuit means responsive to said rectified first and second signal and operative to provide said switching signal having an amplitude commensurate with the in-phase component of said first and second signals.

10. A condition responsive switching system for indicating the occurrence of a condition comprising:

(a) signal generator means including a first tank circuit detunable upon the occurrence of a condition,

,said signal generator means providing a first signal having a frequency which follows the resonance frequency of said first tank circuit;

(b) frequency dependent phase shift means including a second tank circuit fixedly tuned to the frequency of said first tank circuit in the absence of the occurrence of said condition, said phase shift means being responsive to, said first signal and operative to provide a second signal which is substantially 180 degrees out of phase with said first signal when said first signal has a frequency representative of the absence of the occurrence of said condition;

(c) unidirectional current conducting means for rectifying said first and said second signals;

(d) circuit means responsive to said rectified first and second signal and operative to provide pulsed signal, the width of said pulses being proportional to the difference in phase shift of said first and second signals from a 180 degree phase shift; 7

(e) means for filtering and amplifying said pulses to derive a direct current switching signal; and

(f) utilization means responsive to said switching signal for indicating the occurrence of said condition.

11. A condition responsive switching system for providing an indication when a selected object approaches a selected proximity, said switching system comprising:.

(a) signal generator means including a tank circuit responsive to the proximity of said selected object, the resonant frequency of said tank circuit being a function of such proximity, said signal generator means providing a generator signal having a frequency depending on the resonance frequency of said tank circuit;

(b) frequency dependent phase shift means responsive to said generator signal and operative to provide a phase shift in accordance with the frequency of said generator signal, said phase shift means being adjusted to provide a phase shift of substantially 180 degrees at a generator signal frequency correspond- (1) means for utilizing said switching signal and giving an indication when any one of said selected class of objects approaches said selected proximity.

References Cited in the file of this patent UNITED STATES PATENTS Kock June 17, Peck Sept. 30, Kennedy Nov. 30, Petrofi Aug. 15, Higa Jan. 10, Mel-as Nov. 2

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3302746 *Mar 4, 1964Feb 7, 1967Kurt IkrathSelf-excited seismic systems
US3324647 *Aug 11, 1964Jun 13, 1967Parmet CompanyProximity detector
US3364465 *Feb 12, 1962Jan 16, 1968Gen Precision IncMethod for tuning inductive loop vehicle detectors
US3430221 *Sep 27, 1965Feb 25, 1969Barringer Research LtdProximity detector
US3437988 *Oct 1, 1965Apr 8, 1969Henri N AubertMeans for warning of the relative approach of an obstacle in the path of a vehicle
US3518551 *Feb 8, 1968Jun 30, 1970Tesla NpCircuit arrangement for measuring the damping of an oscillation
US3818430 *Apr 30, 1973Jun 18, 1974United Aircraft CorpTraffic detector using balun transformer phase detector
US3909625 *Jul 30, 1973Sep 30, 1975Magic Dot IncTouch actuated electronic switch
US4004216 *Mar 17, 1975Jan 18, 1977Agfa-Gevaert N.V.Apparatus for detecting metallic particles in a flow of dielectric medium
US4613845 *Mar 24, 1983Sep 23, 1986Bois Donald E DuApparatus for preventing operation of machinery by one who is intoxicated
US4893027 *Sep 21, 1987Jan 9, 1990Gebhard Balluff Fabrik Feinmechanischer Erzeugnisse Gmbh & Co.Proximity switch insensitive to interference fields
US5822683 *Apr 5, 1996Oct 13, 1998Ball Aerospace And Technologies Corp.Pseudo-passive transponder device
US7969166Oct 30, 2006Jun 28, 2011Ident Technology AgMethod and circuit for detecting the presence, position and/or approach of an object relative to an electrode
EP1231502A1 *Feb 8, 2002Aug 14, 2002Thomson Licensing S.A.Finger actuaded device having a proximity detector
EP1431805A2 *Feb 8, 2002Jun 23, 2004Thomson Licensing S.A.Finger actuated device having a proximity detector
EP1431806A2 *Feb 8, 2002Jun 23, 2004Thomson Licensing S.A.Finger actuated device having a proximity detector
WO2007048639A1 *Oct 30, 2006May 3, 2007Ident Technology AgMethod and circuit for detecting the presence, position and/or approach of an object in relation to at least one electrode device
WO2007048640A1 *Oct 30, 2006May 3, 2007Ident Technology AgMethod and circuit for detecting the presence, position and/or approach of an object in relation to at least one electrode device
Classifications
U.S. Classification340/551, 340/941, 340/933, 340/561, 324/236, 324/207.26, 307/652, 331/1.00R, 331/65
International ClassificationH03K17/945, H03K17/94
Cooperative ClassificationH03K17/945
European ClassificationH03K17/945