US3764819A - Electronic switch actuated by proximity of the human body - Google Patents

Electronic switch actuated by proximity of the human body Download PDF

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Publication number
US3764819A
US3764819A US00234952A US3764819DA US3764819A US 3764819 A US3764819 A US 3764819A US 00234952 A US00234952 A US 00234952A US 3764819D A US3764819D A US 3764819DA US 3764819 A US3764819 A US 3764819A
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Prior art keywords
capacitance
arrangement
probe
approach
oscillator
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US00234952A
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English (en)
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H Muller
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Individual
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Priority claimed from DE19712112521 external-priority patent/DE2112521C3/de
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/945—Proximity switches
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/945—Proximity switches
    • H03K17/955—Proximity switches using a capacitive detector

Definitions

  • ABSTRACT Foreign Application Prioriiy Data An improved contact-less electronic switch, adapted Mar. 16, 1971 Germany P 21 12 521.3 to be actuated by the approach ofa human hand, with a capacitive probe insulated against the chassis and [52] US. Cl. 307/116, 340/258 C installed in the zone of approach, and connected to a [51] Int. Cl. H0lh 35/00 capacitance detecting circuit which delivers a switch- [58] Field of Search 307/116; ZOO/DIG.
  • an object of the invention to provide an electronic switch suitable for use in the safety circuits of dangerous machines which responds only to the approach of a human hand or potentially to the approach of another part of the human anatomy, but which remains unaffected by the approach of all other materials, such as metals or insulators.
  • a metal part brought into the vicinity of such an electronic switch triggers off first the inductive measuring circuit, so that the logic interconnection according to the invention makes the release of the electronic switch immediately impossible.
  • the approach of an insulating material e.g. plastic, wood, glass, leather, paper and the like, does not affect either the inductive detection circuit, nor the capacitance measuring circuit, so that the logic interconnection according to the invention prevents a signal from being delivered also in this case.
  • the inductive protection circuit does not respond owing to the low capacitance of the approaching object, whilst the capacitance of the capacitive probe is raised to such an extent that the capacitance measuring circuit delivers a switching signal.
  • the conditions for the release of an approach signal are met. responds in principle also to the approach of other parts of the human body; misuse may be avoided simply by mounting the swtich in such a position that it can be reached only the operators hand.
  • the capacitance measuring circuit is adjusted to such a low sensitivity that it does not respond to the approach of insulating material but to the approach of an electrically conducting body.
  • the differential effects on the capacitance of such a probe by insulating materials on the one hand, and by materials with bad electrically conducting properties on the other hand are utilized.
  • the oscillator supplying the inductive probe has preferably a frequency of a few hundred kc/s, whilst the oscillator connected to the capacitive probe operates preferably with frequency in the Mc/s range. In this manner sufficient currents are produced even with comparatively small probe capacitances.
  • the oscillator operates at a frequency of the order of magnitude of a few hundred kc/s. This construction substantially reduces the complexity of the device and ensures the necessary logic interconnection simply in that the oscillator output voltage strongly declines or even collapses on the approach of a metal part, so that the capacitance measuring circuit does not receive a sufficient input voltage to enable it to indicate an increase in the capacitance.
  • the inductive probe is a coil portion of the oscillator. Also this supports an extremely rational production of the electronic switch according to the invention.
  • the initial capacitance of the capacitive probe is neutralized because this substantially increases the response sensitivity for increases in the capacitance.
  • the response threshold of the trigger and preferably also the regenerative coupling factor of the oscillator are adjustable.
  • the invention utilizes the fact that every induction coil also has a capacitance against mass.
  • the part of the coil serving as capacative probe is in this case substantially larger than the remianing part of the coil.
  • the remaining part of the coil contributes in this case to the utilization of the initial capacitance.
  • the part of the coil acting as capacitive probe is arranged in space non-symmertically relative to the remaining part that in the case of the approach of an object changing the capacitance, the changes in the capacitances of the two coil portions against mass are non-proportional. This is the condition for detecting changes in the capacitances by measuring techniques.
  • FIG. 1 is a plan view ofthe key portion of an electronic switch arrangement according to the invention
  • FIG. 2 is a cross-section along the line IIII in FIG.
  • FIG. 3 is a block diagram of the basic construction of an electronic switch according to the invention.
  • FIG. 4 is a block diagram of a substantially simplified embodiment of the electronic switch according to the invention.
  • FIG. 5 is a detailed circuit diagram of the object shown diagrammatically in FIG. 4;
  • FIG. 6 is an axial cross-section of a particularly preferred embodiment of a key portion for an electronic switch according to the invention.
  • FIG. 7 is a preferred circuit for evaluating the signals delivered by the key portion according to FIG. 6.
  • FIGS. 1 and 2 of the drawing a key portion of an electronic switch according to the invention is mounted in an earth, or grounded, metal housing 1.
  • a U-shaped core of powdered iron is arranged in the housing I in such a manner that the ends of the two legs terminate at the level of the upper wall of housing 1.
  • Induction windings3, forming the inductive probe, are mounted on the two legs of the core 2.
  • a metal plate 4 which forms the capacitive probe.
  • the top of the housing is covered by an insulating plate 5 on which the capacitive probe 4 may be mounted from the bottom, so that the housing has no protruding parts.
  • FIG. 2 shows also in solid lines the lines of the magnetic field, in dotted lines the lines of the electric field, and, by way of illustration, a hand 6 approaching the switch.
  • the earthed, or grounded, metal housing ll forms the counter-electrode for the capacitive probe 4, so that approaches from the side of the housing remain ineffective.
  • the block diagram of FIG. 3 shows diagrammatically the connection of the inductive probe 3 and of the capacitive probe 4 forming the permeating fields.
  • the winding of the probe 3 is the coil portion of an oscillator 8, operating at a frequency of a few hundred kc/s.
  • the output voltage of the oscillator 8 is applied to a 7 threshold means 11 with a threshold which supplies an output signal L during the normal operation of the oscillator 8 and an output signal 0 when the threshold of the oscillator output voltage is not reached.
  • the output of the threshold means 11 is applied to one input of an AND gate 12.
  • the capacitive probe 4 which is according to the invention structurally combined with the inductive probe 3, isconnected with the housing l as counter-electrode to a circuit responding to changes in the capacitance, briefly referred to as capacitance measuring circuit this circuit has also a threshold so that it delivers under normal conditions an output signal 0 and supplies an output L only when a certain increase in the capacitance of the probe 4 is present.
  • the output of the circuit 10 is applied to the other input of the AND gate l2.
  • the capacitive probe 4 is supplied by an oscillator with a frequency of several Mc/s.
  • the output 15 of the AND gate 12 delivers an output signal L" only if an L signal and an L signal is present at its inputs. In all other cases, the output 15 carries the output signal 0.
  • the oscillator 8 If a metal part is brought into the proximity of the key according to FIGS. I and 2, the oscillator 8 is damped and the output voltage of the oscillator 8 drops below the threshold of the gate 11, so that the corresponding input of the AND gate 12 receives the input signal 0. Hence, the output 15 will deliver the signal 0 irrespective of the output of the capacitance measuring circuit 10. In other words, the switch will not be actuated even by approaching the metal part further to the key.
  • the output voltage of the oscillator 8 does not drop below the threshold of the gate 1 1, so that the corresponding input of the AND gate 12 delivers the signal L even with the insulating material in close proximity. Since according to the invention the threshold of the capacitance measuring circuit 10 is so high that the comparatively low increase in the capacitance, caused by the insulating material, cannot lead to the threshold being exceeded, the second input of the AND gate 12 receives the signal 0 so that also in this case the output signal will be 0. Also in this case, the switch does not respond.
  • the resulting small damping of the oscillator 8 owing to the correct setting of the threshold in the threshold means 11 does not cause the oscillator voltage to drop below this threshold.
  • the output signal of the threshold means 1 1 remains, therefore, L.
  • the approach of the hand 6 causes the capacitance of the probe 4 to increase to such an extent that the threshold of the capacitance measuring circuit 10 is exceeded, and the output of the circuit delivers the signal L. Since now inputs of the AND gate 12 receive the signals L and L, the output 15 delivers the signal L" and the switch according to the invention responds.
  • the switch may be actuated by human hand 6, even if the hand is protected by a strong leather glove, such as in the case, e.g., of processing sheet metal.
  • the two fields of the switch according to the invention penethe capacitive probe 4.
  • the partial winding supplying the voltage to the probe 4 is connected to a capacitance current or voltage converter 19, which is followed by a trigger whose output 21 supplies normally the output signal 0, but which supplies an output signal L" when the output current or the output voltage of a converter l9 exceeds the threshold of the trigger 20.
  • the capacitance converter 19 operates in its linear range in accordance with the following relation:
  • the approach of a smaller or larger metal component to the key containing the probes 3 and 4 will give rise to an increase in the capacitance, but simultaneously the oscillator damping will cause the voltage U to drop.
  • the sensitivity of the converter 19 is strongly reduced, so that the threshold of the trigger 20 cannot be exceeded even with a strong increase in the capacitance.
  • the oscillation of the oscillator may even collapse completely, so that the output of the converter 19 no longer presents an output signal.
  • FIG. 5 A detailed circuit diagram is shown in FIG. 5.
  • the oscillator 17 consists substantially of a transistor 22, the collector of which is'connected with the winding 3, forming an inductive coupling winding 23 of the inductive probe.
  • the oscillating circuit determining the frequency is formed by the winding 3 and the capacitor 16.
  • the regenerative feedback is effected by a further winding 25 and a variable resistor 26 serving for adjusting the regenerative feedback factor.
  • a capacitor 27 mounted between resistor 26 and the emitter produces the galvanic decoupling.
  • Resistors 28, 29 and 30 adjust the working point of the transistor 22, whilst a capacitor 31 connects the base of the transistor 22, operating in a base circuit, to earth.
  • the arrangement is supplied by a d.c. voltage source, shown at The winding 3 is divided into two partial coils by a tap 24.
  • the capacitive probe 4 is connected to the lower end of the upper partial coil, whilst the upper end of the upper partial coil is earthed through a trimming capacitor 38.
  • the capacitance converter 19 is realized by a known diode pump consisting of diodes 32, 33, a resistor 35, and a capacitor 36. By means of a capacitor 37, the base of the diode is earthed. The diode pump is connected to the tap 24 of the coil 3.
  • the capacitor 38 is so chosen and adjustable that the initial capacitance of the probe 4 can be neutralized.
  • Adjacent to the diode pump is a filter member consisting of a resistor 39 and a capacitor 40.
  • the d.c. voltage produced in this manner is applied to the noninverting input of an operational amplifier 41 which is fed back by means of resistors 42, 43, and 44 in such a way that it behaves like a trigger.
  • the inverting input of the operational amplifier 41 is connected to the tap of a potentiometer 46 through a resistor 45 which is necessary for reasons of compensating the offset. According to the invention, the adjustment of the potentiometer 46 can be used for adjusting the threshold of the trigger formed by the operational amplifier 41.
  • Zener diodes 47, 48 and a series resistor 49 in the voltage lead serve to stabilize the supply voltages of the circuit.
  • the output of the trigger is connected to a voltage divider consisting of resistors 50, 51 through which the base of a switching transistor 52 is controlled. This transistor controls directly a relay 53.
  • a diode 54 in the collector circuit of the transistor 52 serves to chop inductive voltage peaks.
  • the capacitance converter may also realize by a circuit other than a diode pump, e.g. the output voltage of the capacitive probe can be rectified as a function of the phase.
  • FIGS. 6 and 7 shows a further important possibility of simplifying the electronic switch according to the invention, wherein the intrinsic capacitance of the winding 3 is used at least partially for forming the capacitive probe 4.
  • the fact that the intrinsic capacitance of the winding 3 in FIG. 6 is used partially, is indicated in the drawing by marking the relevant part 30 of the winding additionally by a dotted line loading to reference numeral 4.
  • the winding 3 is arranged in the FIG. 6 embodiment in a high frequency iron pot core 7, in which a tap is provided between the outer partial winding 3b and the larger inner partial winding 30.
  • the larger partial winding 30, serving as capacitive probe 4 is arranged in space non-symmetrically to the remainder of the winding 3b, so that the changes in the intrinsic capacitances of the partial windings 3a and 3b, caused by approaching objects, are non-proportional, because otherwise the capacitance converter 19 connected to the windings would deliver no signal in the case of changes in the capacitance.
  • FIG. 7 A preferred, particularly simple circuit for connecting the switch of FIG. 6 is shown in FIG. 7.
  • the capacitor 16 forms with the winding 3 the oscillating circuit of an oscillator, not shown.
  • the transistor 22, the diode 13, the capacitor 14 and the output resistor 9 form a capacitance converter 19. Between the voltage terminals there is a capacitor 57, forming a high frequency short circuit. In this circuit, a change of the capacitance of the partial winding 3a relative to earth brings about a change of the current through the resistor 9.
  • the lower end of the partial winding 3b is connected to earth through a trimmer capacitor 58, which is constructed and adjustable in such a manner that the initial capacitance of the coil 3 can be neutralized.
  • the output 59 of the circuit may be applied to a trigger 20 as shown in FIGS. 4 and 5.
  • said inductive probe consists of a coil mounted on the legs of a U-shaped high frequency iron core and said capacitive probe consists of ametal plate disposed to lie between the two legs of said iron core but in spaced relationship thereto.
  • an electronic switching arrangement comprising a switch actuated in a contact-less manner by the approach of a portion of a human body, comprising a coil divided into two partial windings, means including one of said windings connected to a capacitor to form an oscillator circuit of an oscillator, the other of said windings being connected to a capacitive probe and applying an electrical potential thereto; said capacitive probe being connected to a capacitance voltage converter circuit; said converter circuit being connected to a trigger; said trigger having a response threshold which is above the level of the signal supplied by said converter circuit in the absence of an object in a zone proximate to the switch and means whereby said response threshold of said trigger is exceeded when a portion of a human body is in the zone proximate to the switch.
  • said capacitance converter circuit comprises a diode pump.
  • a switch actuated in a contact-less manner by the approach of a portion of a human body comprising a high frequency iron pot core, a coil disposed in said core, said coil being tapped to provide two partial windings,
  • one of said partial windings being larger than the other of said partial windings, said one of said partial windings being arranged in space non-symmetrically with respect to said other of said partial windings; means including said coil connected to a capacitor to form an oscillator circuit of an oscillator; said coil being connected to a capacitance converter circuit; said converter circuit being connected to a trigger; said trigger having a response threshold which is above the level of the signal supplied by said converter circuit in the absence of an object in a zone proximate to the switch and means whereby said response threshold of said trigger is exceeded when a portion of a human body is in the zone proximate to the switch.

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  • Electronic Switches (AREA)
  • Switches That Are Operated By Magnetic Or Electric Fields (AREA)
  • Inductance-Capacitance Distribution Constants And Capacitance-Resistance Oscillators (AREA)
US00234952A 1971-03-16 1972-03-15 Electronic switch actuated by proximity of the human body Expired - Lifetime US3764819A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19712112521 DE2112521C3 (de) 1971-03-16 Von einer Annäherung der menschlichen Hand berührungslos auslösbarer elektronischer Schalter
CH352572A CH548698A (de) 1971-03-16 1972-03-10 Schaltungsanordnung zur abgabe eines annaeherungssignals bei annaeherung eines menschlichen koerperteiles.

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US3764819A true US3764819A (en) 1973-10-09

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US (1) US3764819A (de)
AT (1) AT312734B (de)
BE (1) BE780612A (de)
CH (1) CH548698A (de)
DE (1) DE2311249C3 (de)
FR (1) FR2129692A5 (de)
IT (1) IT950118B (de)

Cited By (52)

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US3919596A (en) * 1973-01-31 1975-11-11 Robert Elliott Bellis Touch sensitive power control system
US4081700A (en) * 1976-06-16 1978-03-28 Hamilton Ii William F Touch control switch circuit with compensation for power supply line fluctuations
FR2434524A1 (fr) * 1978-08-22 1980-03-21 Hansa Metallwerke Ag Montage pour un interrupteur d'approche, plus particulierement utilisable pour des installations sanitaires
US4553040A (en) * 1982-07-06 1985-11-12 Trueper Dirk Inductive proximity switch
US4675659A (en) * 1986-02-10 1987-06-23 Jenkins Jr Dale C Method and apparatus for signaling attempted suicide
WO1987006010A1 (en) * 1986-03-27 1987-10-08 Duracell International Inc. Capacitive sensor and metal detector for detecting concealed objects
US4859931A (en) * 1986-12-23 1989-08-22 Matsushita Electric Works, Ltd. Electronic detector with capacitor sensor and magnetic field sensor for locating an object behind a wall surface
WO1993012530A1 (en) * 1991-12-11 1993-06-24 Square D Company Two hand operated machine control station using capacitive proximity switches
US5255341A (en) * 1989-08-14 1993-10-19 Kabushiki Kaisha Toshiba Command input device for voice controllable elevator system
FR2733783A1 (fr) * 1995-05-04 1996-11-08 Kiekert Ag Dispositif de securite sur un vehicule automobile, qui ne permet l'ouverture du vehicule automobile que par une personne autorisee a ouvrir le vehicule automobile
EP0751403A1 (de) * 1995-06-30 1997-01-02 Carlo Gavazzi AG Kombinierter Sensor
US5652577A (en) * 1994-10-27 1997-07-29 Frasier Products, Inc. Device and method for passively activating inductive loop sensor
US5729604A (en) * 1996-03-14 1998-03-17 Northern Telecom Limited Safety switch for communication device
US5757196A (en) * 1995-09-28 1998-05-26 Endress + Hauser Gmbh + Co. Capacitive switch actuated by changes in a sensor capacitance
US5801340A (en) * 1995-06-29 1998-09-01 Invotronics Manufacturing Proximity sensor
EP0955431A1 (de) * 1998-05-05 1999-11-10 Valeo Securite Habitacle Sicherheitssystem für eine Kraftfahrzeugöffnung
US6259486B1 (en) 1999-10-20 2001-07-10 A. Pascal Mahvi Sensor unit for controlling television set operation
US20040090730A1 (en) * 2002-11-08 2004-05-13 Byrne Daniel J. Active elecrostatic discharge event prediction and countermeasure using charge proximity sensing
US20040238742A1 (en) * 2003-05-29 2004-12-02 Mahvi Ali Pascal Infrared sensor unit for controlling operation of electrically powered appliances
US20060054724A1 (en) * 2004-09-10 2006-03-16 Fellowes Inc. Shredder with proximity sensing system
US20060054725A1 (en) * 2004-09-10 2006-03-16 Fellowes, Inc. Shredder throat safety system
US7013570B2 (en) 2003-06-18 2006-03-21 Irwin-Industrial Tool Company Stud finder
GB2418741A (en) * 2004-10-01 2006-04-05 Ford Global Tech Llc Control system for a sliding roof and powered windows of a vehicle
US20060219827A1 (en) * 2004-09-10 2006-10-05 Fellowes Inc. Shredder with thickness detector
US7178250B2 (en) 2004-07-21 2007-02-20 Irwin Industrial Tool Company Intersecting laser line generating device
US20070246582A1 (en) * 2006-04-24 2007-10-25 Acco Uk Limited Shredding machine
US7344096B2 (en) 2004-04-02 2008-03-18 Fellowes Inc. Shredder with lock for on/off switch
WO2008042538A2 (en) * 2006-09-28 2008-04-10 Fellowes, Inc. Shredder with intelligent activation switch
US20090032629A1 (en) * 2007-08-02 2009-02-05 Acco Uk Limited Shredding machine
US7487596B2 (en) 2004-06-25 2009-02-10 Irwin Industrial Tool Company Laser line projected on an edge of a surface
US20090090797A1 (en) * 2007-10-04 2009-04-09 Fellowes Inc. Shredder thickness with anti-jitter feature
US7737841B2 (en) 2006-07-14 2010-06-15 Remotemdx Alarm and alarm management system for remote tracking devices
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US7804412B2 (en) 2005-08-10 2010-09-28 Securealert, Inc. Remote tracking and communication device
US20100243774A1 (en) * 2009-03-24 2010-09-30 Fellowers, Inc. Shredder with jam proof system
US20100288861A1 (en) * 2009-05-15 2010-11-18 Fellowes, Inc. Paper alignment sensor arrangement
US20100320299A1 (en) * 2009-06-18 2010-12-23 Fellowes, Inc. Restrictive throat mechanism for paper shredders
US7936262B2 (en) 2006-07-14 2011-05-03 Securealert, Inc. Remote tracking system with a dedicated monitoring center
US8201761B2 (en) 2009-01-05 2012-06-19 Fellowes, Inc. Thickness sensor based motor controller
US8232876B2 (en) 2008-03-07 2012-07-31 Securealert, Inc. System and method for monitoring individuals using a beacon and intelligent remote tracking device
US8382019B2 (en) 2010-05-03 2013-02-26 Fellowes, Inc. In-rush current jam proof sensor control
US8463288B2 (en) 2010-06-18 2013-06-11 The Invention Science Fund I, Llc Irradiation self-protection from user telecommunication device
US8462002B2 (en) 2010-06-18 2013-06-11 The Invention Science Fund I, Llc Personal telecommunication device with target-based exposure control
US8511593B2 (en) 2010-05-28 2013-08-20 Fellowes, Inc. Differential jam proof sensor for a shredder
US8514070B2 (en) 2010-04-07 2013-08-20 Securealert, Inc. Tracking device incorporating enhanced security mounting strap
US8519856B2 (en) 2010-06-18 2013-08-27 The Invention Science Fund I, Llc Mapping system for irradiation protection
US8550387B2 (en) 2009-06-18 2013-10-08 Tai Hoon K. Matlin Restrictive throat mechanism for paper shredders
US8672247B2 (en) 2005-07-11 2014-03-18 Fellowes, Inc. Shredder with thickness detector
US8686865B2 (en) 2010-06-18 2014-04-01 The Invention Science Fund I, Llc Interactive technique to reduce irradiation from external source
US8797210B2 (en) 2006-07-14 2014-08-05 Securealert, Inc. Remote tracking device and a system and method for two-way voice communication between the device and a monitoring center
US8870106B2 (en) 2004-09-10 2014-10-28 Fellowes, Inc. Shredder with thickness detector
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FR2531212B1 (fr) * 1982-07-30 1986-04-11 Metraflu Capteur acoustique de proximite
WO1987004851A1 (en) * 1986-01-30 1987-08-13 Intellect Electronics Ltd. Proximity sensing device
US6320282B1 (en) 1999-01-19 2001-11-20 Touchsensor Technologies, Llc Touch switch with integral control circuit
US7906875B2 (en) 1999-01-19 2011-03-15 Touchsensor Technologies, Llc Touch switches and practical applications therefor
DE10163778B4 (de) * 2001-06-27 2008-01-24 Witte-Velbert Gmbh & Co. Kg Griff mit integrierter Antenne und Sensorelektrode
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US3510677A (en) * 1966-08-12 1970-05-05 Euclid Electric & Mfg Co The Electronic detection system
US3469204A (en) * 1967-09-14 1969-09-23 Whittaker Corp Proximity sensitive on-off oscillator switch circuit
US3609735A (en) * 1968-12-03 1971-09-28 Harris Intertype Corp Inductive-capacitive probe in machine for handling sheetlike material

Cited By (104)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3919596A (en) * 1973-01-31 1975-11-11 Robert Elliott Bellis Touch sensitive power control system
US4081700A (en) * 1976-06-16 1978-03-28 Hamilton Ii William F Touch control switch circuit with compensation for power supply line fluctuations
FR2434524A1 (fr) * 1978-08-22 1980-03-21 Hansa Metallwerke Ag Montage pour un interrupteur d'approche, plus particulierement utilisable pour des installations sanitaires
US4553040A (en) * 1982-07-06 1985-11-12 Trueper Dirk Inductive proximity switch
US4675659A (en) * 1986-02-10 1987-06-23 Jenkins Jr Dale C Method and apparatus for signaling attempted suicide
WO1987006010A1 (en) * 1986-03-27 1987-10-08 Duracell International Inc. Capacitive sensor and metal detector for detecting concealed objects
US4853617A (en) * 1986-03-27 1989-08-01 Keith Douglas Apparatus having capacitive sensor and metal detector for detecting objects concealed behind surfaces
US4992741A (en) * 1986-03-27 1991-02-12 The Stanley Works Capacitive sensor and metal detector with a display for quantitatively displaying signals resulting from concealed objects
US4859931A (en) * 1986-12-23 1989-08-22 Matsushita Electric Works, Ltd. Electronic detector with capacitor sensor and magnetic field sensor for locating an object behind a wall surface
US5255341A (en) * 1989-08-14 1993-10-19 Kabushiki Kaisha Toshiba Command input device for voice controllable elevator system
WO1993012530A1 (en) * 1991-12-11 1993-06-24 Square D Company Two hand operated machine control station using capacitive proximity switches
US5341036A (en) * 1991-12-11 1994-08-23 Square D Company Two hand operated machine control station using capacitive proximity switches
US5652577A (en) * 1994-10-27 1997-07-29 Frasier Products, Inc. Device and method for passively activating inductive loop sensor
FR2733783A1 (fr) * 1995-05-04 1996-11-08 Kiekert Ag Dispositif de securite sur un vehicule automobile, qui ne permet l'ouverture du vehicule automobile que par une personne autorisee a ouvrir le vehicule automobile
US5801340A (en) * 1995-06-29 1998-09-01 Invotronics Manufacturing Proximity sensor
EP0751403A1 (de) * 1995-06-30 1997-01-02 Carlo Gavazzi AG Kombinierter Sensor
US5757196A (en) * 1995-09-28 1998-05-26 Endress + Hauser Gmbh + Co. Capacitive switch actuated by changes in a sensor capacitance
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Also Published As

Publication number Publication date
DE2112521B2 (de) 1976-07-08
DE2311249B2 (de) 1980-03-06
CH548698A (de) 1974-04-30
DE2112521A1 (de) 1972-09-21
BE780612A (fr) 1972-07-03
AT312734B (de) 1974-01-10
IT950118B (it) 1973-06-20
DE2311249C3 (de) 1980-11-06
FR2129692A5 (de) 1972-10-27
DE2311249A1 (de) 1973-09-13

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