DE10003913A1 - Interrupt recognition device has metallic object that form open magnetic circuit with coil pairs, and which conducts to dampen induced voltage to secondary windings of second coil pair - Google Patents

Abstract

The primary windings (3/1) and secondary windings (2/2,3/2) of each coil pair (2,3) are arranged one over the other. The coil pairs form an open magnetic circuit with a metallic object (9/1) that electrically conducts to increasingly dampen the induced voltage to the secondary windings (3/2) of the coil pair (3).

Description

The invention relates to a device for an inductive sensor, this detects all electrically and magnetically conductive objects, there will be determined by the proximity switch one or more switching distances derive a function therefrom according to the preamble of claim 1.

DE 42 04 334 C2 describes such a device for detecting the Interruptions in the metallic tracks are known, in which the Vehicle from a specific location through a contactless, inductive Coupling is directed to a specific destination. The device has one Steering drive, a drive motor and control logic. For inductive Coupling becomes one of the two lying side by side in the direction of travel Coil pairs used, each with a primary winding and one Secondary winding, the end faces of each parallel to a metallic track are aligned and when the two primary windings are energized in the voltages are induced in each of the two secondary windings, one Secondary voltage is used to control the drive motor through the control logic evaluates. The two pairs of coils, including the metallic track, each as open magnetic circuit are formed, and the metallic path electrically is designed to conduct with increasing coverage with the end face of a coil pair an increasing damping of the induced voltage in to effect the secondary winding of a pair of coils. The two pairs of coils are components of two sensors, the output signal of one sensor is one direct measure of the detection of an interruption in the metallic path.  

According to this output signal, the drive motor of the vehicle controlled.

This sensor consists of a pair of coils with a primary and Secondary winding. The detection of a gap in the metallic orbits derived from a secondary voltage of a pair of coils, whose amplitude increases when the metallic tracks are broken because of the metallic ones Paths can not dampen the secondary voltage. Has the Coil pair to the metallic tracks a distance of less than 10 mm, and are the metallic tracks are about 100 mm wide, so is a detection Interruption in the metallic tracks is always guaranteed. Are the metallic sheets made of spring steel (50 mm wide, 0.2 mm thick), and the pair of coils has a ground clearance of 20 mm to the metallic tracks the change in a secondary voltage is very small. At a Experimental setup with the conditions mentioned above, the Secondary voltage from 28 V to 28.3 V with an interruption in the metallic train. A doubling of the secondary turns only leads to a signal increase of 0.6 V, with a basic signal of 56 V. Because of the Temperature fluctuations, and because of an influence of the current pulse due to aging tolerances of the components, a reliable evaluation of the Secondary signal very difficult under these circumstances.

Proximity switches are known, which by means of a parallel resonance circuit a capacitance and an inductor and an operational amplifier become. After switching on the operating voltage, the oscillates Operational amplifiers with a frequency of 100 kHz or up to max. 1 MHz. The Sensor coil is in a shell core made of a highly permeable ferrite material integrated so that a field is formed at the shield opening of the housing. If there is an electrical object in this field, the alternating electromagnetic field and there will be after  Induction law creates eddy currents that draw energy from the field. Becomes now a metallic object is so close to the operational amplifier the necessary energy is no longer available and the oscillation breaks together. This cause leads to this through a control logic When the switch in the proximity switch is switched on. A hysteresis ensures that the switch cannot bounce. The advantage of this sensor is that it can be operated with a few microwatts of electrical energy. The shell core causes additional tolerances, with a certain one Design are the permissible variations due to the operating voltage and Ambient temperature fluctuations are relatively large. When using a Standard switch and axial approach of the standard measuring plate results for one certain type a range from 0 to 8.1 mm where the switch is safe is switched on. The measuring plate must have a minimum distance of 13.9 mm so that the switch is safely turned off. The mechanical lifting movement must at least 5.8 mm when approaching axially. To tolerances The manufacturer recommends reducing the measuring plate radially to To move the proximity switch. A conventional proximity switch can only do one Detect switching distance, the accuracy of the switching distance is very low is. Another disadvantage is that a certain type of Proximity switch, the response time increased from 0.1 ms to 5 ms if the switching distance of the measuring plate increases from 1 mm to 10 mm. Through the The proximity switch coil is turned on with a capacitor Parallel resonance circuit formed, the oscillation does not occur, this is a direct measure of the switching distance of the sensor to the electrically conductive object. In accordance with this switching state 'On or Off', the switching distance becomes detected an electrically conductive object.

For the device of the precise inductive proximity switch are always used two pairs of coils and evaluated its difference signal. The two  Coil pairs can be formed by a primary coil and two secondary coils The two pairs of coils can also be replaced by two primary coils and two Secondary coils are formed. These two pairs of coils are e.g. B. axially arranged one above the other so that two pairs of coils for inductive coupling serve, a pair of coils always serves as a sensor and is paired with a sensor coil referred to, this is arranged at the shield opening of the housing to detect an electrically conductive object, the pair of coils facing away is not aimed at the electrically conductive object. The distance of the Coil pair facing away from the sensor coil pair must be so large that it cannot be influenced by the electrically conductive object. That induced Secondary signal of this pair of coils always has the same amplitude as that Sensor coil pair if the sensor coil pair in no way by one foreign metallic object can be dampened, and because the two Secondary coils are connected in series so that they compensate for each other Differential signal always 0 volts. Is the switching distance to a metallic object relatively large, a slight change in the differential signal can be assured be evaluated. With a pair of coils with two primary coils there is spatial X / Y / Z position of the pair of coils facing away from the pair of sensor coils as desired, because the secondary signal of this pair of coils only does the two very job to compensate for high secondary voltages.

Here is the advantage of the invention listed the disadvantages at the outset to eliminate the type mentioned, for the device of the precise inductive Proximity switches use two pairs of coils, with no shell core is necessary, the inductive coupling is done by an open magnetic Circle. When the measuring plate approaches the proximity switch axially, n Distance ranges can be determined. If a high switching distance is desired, then can be increased by increasing the gear ratio Diameter of the two pairs of coils, and by increasing the thickness of the  metallic or magnetic objects sensitivity significantly be increased. An increase in the operating voltage causes a higher one Current pulse and an increase in the possible switching distance. The max. The response time of the switch is determined by the cycle time of the pulse generator determined, it remains in the entire switching range of the measuring plate unchanged. The difference signal can be positive or negative, depending on the which of the two coil pairs by an electrically or magnetically conductive Object is damped, in the exemplary embodiment, a positive difference signal generated. The reason is because the negative secondary signal is attenuated and the positive difference signal remains constant. The operating voltage changes to the basic position, d. H. without a metallic object, this does not lead to any Change in the differential signal because the two pairs of coils are connected in series are that the secondary signals compensate each other. The electric conductive object generates eddy currents and deprives the sensor coil pair of field Energy and this changes the difference signal, the field of the averted Coil pair remains unchanged. The object consists of a ferrite material or a ferrite pin, the polarity of the difference signal is inverted because the Field energy is increased. The dimensions of the two change The difference signal remains in the coil pairs due to a temperature change Basic position almost unchanged because the dimensions of both Change coil pairs at the same time. Interference from external influences can usually have no effect because of interference currents on both pairs of coils act and compensate each other, because both pairs of coils in Are connected in series that the interference signals of both pairs of coils compensate. To keep the capacity of the secondary windings low a coil wire with insulation can be used, any material that good electrical conductivity is suitable as coil wire.  

Small tolerances of the switching distance can be achieved by a stable mechanical construction of the two pairs of coils can be achieved, their location must remain the same to each other. Both pairs of coils are in the housing potted, the mechanical stability increases. A housing shield, e.g. B. an aluminum tube with an external thread ensures stable behavior with external influences.

This is due to the manufacturing tolerances of both pairs of coils Difference signal in the basic position is not always 0 volts. A comparison of the Difference signal can e.g. B. by reducing the number of turns of the primary or secondary coil can be achieved, this is usually too expensive. If the two pairs of coils consist of three coils, two coils are fixed and a coil is adjusted in the axial direction until the difference signal Voltage value of 0 volts. If the two pairs of coils consist of four coils, First three coils are fixed, the fourth coil is used for adjustment. If the difference signal is not 0 volts in the basic position, it is possible to To dampen the coil pair by a small piece of metal, e.g. B. by a self-adhesive aluminum foil on the front of a pair of coils is attached. The adjustment should always take place when installed. He follows the manufacture of the pair of coils with very small tolerances is not absolutely necessary that the differential signal in the basic position Voltage value is 0 volts, you only have to pay attention to the polarity. By two adjustable resistors can e.g. B. two switching distances one Proximity switches can be set.

The differential signal does not have to be in the basic position of the proximity switch have the voltage value of 0 volts, it can be a negative or positive Have amplitude. This can be achieved that the tolerance of a Switching distance when the operating voltage changes, becomes smaller if exactly in the switching distance by a metallic object, the difference signal  the voltage value of 0 volts is damped. The switching distance is z. B. by an adjustable resistance adjusted by the user. To one if possible The difference signal in the basic position will reach a large switching distance adjusted to the value of 0 volts.

If the two pairs of coils have only one primary coil, this is in the middle arranged and this induces a secondary signal in each secondary coil Secondary signal is positive, the other is negative, both have in the Home position the same amplitude, so there is no difference signal because both secondary coils are connected in series so that their signals compensate.

If each coil pair has a separate primary coil, the switching distance can be increased, it is appropriate to end the wire of the first Coil pair of the primary winding with the end of the wire facing away To connect the pair of coils of the primary winding, because then their Compensate for magnetic fields. This can be seen from the fact that repel both pairs of coils. The coil pairs can be on two or four coils have to be wound, the bobbin does not apply to baking coils, large Coil pairs can be laminated on a circuit board.

Due to the aforementioned measures, a higher one Sensitivity reached, the amplitude of the difference signal increases Approach the electrically conductive object. Can always be of the same Object can be assumed, the switching distance from the height of the Amplitude of the difference signal can be derived, the accuracy of the Switching distance is significantly larger. The exact inductive proximity switch can have several switching distances, it has two switching distances, z. Legs external load can be switched on at a switching distance of 15 mm The external load is switched off e.g. B. at a switching distance of 3 mm.  

In a test arrangement, the difference signal of the two reaches Coil pairs with two separate primary windings, at one operating voltage of 20 volts a positive amplitude of 4 volts, with a switching distance of 0 mm, whereby the metallic object from a 1 mm thick aluminum plate consists. The two pairs of coils have a max. Winding diameter of 18 mm, the primary coils have 60 turns with a wire diameter of 0.4 mm, the secondary coils have 200 turns, with one Wire diameter of 0.2 mm. The two secondary coils are low-resistance completed and have a terminating resistance of 1 kΩ to one to achieve additional interference protection. With a metallic housing Differential signal additionally damped so that the damping is not too strong the ohmic resistance of the secondary coils should not be too great, moreover the coils should have a certain clearance to the housing. The Sensor coil pair is arranged on the edge of the housing. The sensitivity of this Experimental arrangement can be further increased by the Secondary number of turns is increased because by increasing the Gear ratio a multiplication of the difference signal is possible.

It is understandable that because of the magnetic excitation of the primary coil, the operating current is higher than usual. In a test arrangement of the current pulse is 1, 8 A, the leading edge is 15 microseconds long, at an operating voltage of 20 volts. Due to the current pulse, an additional operating current of 10 mA must be expected with a cycle time of 1 ms. The response time is identical to the cycle time, and this determines the operating current of the exact proximity switch. The response time is the same for every switching distance of the proximity switch. The two pairs of coils are optimized if, due to the approach of the measuring plate, the max. possible difference signal can be achieved. Given the diameter of the proximity switch, the optimal choice of coil width and the choice of wire diameter for both pairs of coils play a major role. The amplitude of the current pulse is determined by the inductive and ohmic resistance of the primary coils and by the operating voltage. It is advisable to use a thicker wire diameter for the primary coils than for the secondary coil, the ohmic resistance should not be more than 10% to 20% of the total resistance.

The cycle time is in the basic position to reduce the operating current higher, the first time a metal object is recognized, the Cycle time. The distance measurement is about the path of the object that it is during one cycle duration, imprecise.

As a rule, a shell core is not made of a highly permeable ferrite material required, in special applications these can be used to increase the serve magnetic field, for the two pairs of coils one or two Cup cores are used.

As a rule, the two pairs of coils have the same dimensions and have the same number of turns. But it can be useful not keeping the number of turns the same, or the second pair of coils to reduce the diameter for reasons of space, the guideline is that both Coil pairs have the same inductance, and that the wire lengths of both Secondary coils are the same length.

A transistor, MOSFET, thyristor can be used as the output semiconductor switch or triacs can be used. The design of the switch depends on the connected load. One advantage is the programmability of the Proximity switch as opener or closer. The bounce-free switch can be used as Two-wire, three-wire or four-wire switches can be designed. A Parallel connection or series connection of several proximity switches according to the known method. The embodiment shows a three-wire Switch with an n-switching type, with a low external load can  this can also be used as a two-wire switch. The proximity switch is against overvoltage by a voltage-dependent resistor or a Zener diode protected. The switching stage has a protective circuit and the Outputs can therefore be reversed.

The object was achieved by means of two axially one above the other Coil pairs. To detect the electrically or magnetically conductive objects only the pair of sensor coils is aligned with the object. The difference signal of the two pairs of coils is in the basic position to the value of 0 volts adjusted. At a very short distance from the metallic object, and a complete coverage of the sensor coil pair by the electrical conductive object, the difference signal rises to the max. Amplitude at that Secondary signal of the sensor coil pair is damped very strongly, that Secondary signal of the opposite coil pair always reaches the highest possible voltage value. The polarity of the difference signal is positive if the pair of sensor coils is covered by the electrically conductive object. At the Exchanging the functions of the two pairs of coils is now averted Coil pair to the sensor coil pair, so the functions are fully retained However, the polarity of the difference signal becomes negative. A slight change of the difference signal is now perfect for a safe evaluation sufficient because the two pairs of coils are connected in series so that Compensate both secondary signals in the basic position.

Another advantage of the invention is that external influences Cause current impulse through both pairs of coils, this disturbance can but do not affect because the two pairs of coils are connected in series so that compensate for both interference signals.

Driverless industrial trucks are used in the AGV area for Track guidance is used in part by real de-energized guidance tracks. These leading tracks are usually made of stainless spring steel, and are in the  Usually 50 mm wide and 0.3 mm thick. They are preferred because they are higher have mechanical strength. The damping effect of these guide tracks is comparable to an aluminum foil sheet with a thickness of approx. 0.01 mm. Are two proximity switches arranged in a vehicle so that they are in the direction of travel considered side by side, so can by the Difference signals of both proximity switches the position to the center of the leading track be determined. If both difference signals have the same value, that is Guide track in the middle of both proximity switches. Is the difference signal of the right arranged proximity switch higher, the vehicle is too far to the right of the middle of the lead track. With the same arrangement of the proximity switches and with the difference that two difference signals are not evaluated here, but rather 3 switch distances of the two proximity switches. The first Switching distance is reached when a third of the coil face of one Proximity switch is congruent with the guide track, the second switching distance is triggered when a two thirds of the coil face with the lead track is congruent, the third switching distance is triggered when the full The end face of the coil coincides with the lead track. That way the position of the truck is determined by three switching distances.

An application of the invention is contemplated to e.g. B. one mechanical position switch through a non-contact switch replace. A precise position can be determined by the exact proximity switch a movable metallic part or there can be n spacing areas be measured. With the help of a very small in diameter Proximity switch can e.g. B. a laminated bar code on a circuit board to be read. A wide application is e.g. B. a closure check of Bottles, provided that a metal cap is used. On Use of the proximity switch is possible if e.g. B. non-ferrous metals separated should be. With the help of a proximity switch, a weld can also be made  be checked. The possible uses are versatile, one use is too recommend use when environmental influences such as dust, moisture, vibration of a mechanical switch would impair the function. Likewise can change the density of the electrically conductive materials in liquids by the Coil pairs can be determined. The electrical conductivity of a metallic Part is determined by the material thickness factor. With proximity switches the thickness of the standard measuring plate is 1 mm.

The device for accurate proximity switches also detects objects a magnetically conductive material, the higher its magnetic conductivity is, the larger the field increase, and the higher the max. possible amplitude of the difference signal of the now inverted difference signal, when the sensor coil pair is covered by a ferrite material. The magnetic object can be a ferrite pin or shell core that is in a Immersed pair of coils, this increases the max. possible switching distance. The direction of movement of the object can be axial or radial, the formation the metallic or magnetic object can be any. Through the A metallic object can polarity of the difference signal positive or negative be distinguished from a magnetic object.

To avoid electrical and magnetic interference the two pairs of coils and the control logic are protected by a metal housing. Only the side of the case that faces the metallic or magnetic object is directed through a cover made of a non-metallic material protected.

For special versions and two primary coils, the pair of coils, the for compensation serves outside the housing of the proximity switch be arranged. With small coil pairs in diameter can Increasing the inductive coupling wound both coil wires together  become. The coil pairs can also be produced by means of micromechanics become.

The present invention is based on the object Device of the type mentioned electrically and magnetically conductive objects to identify.

This object is achieved by a device with the features of Claim 1 solved.

Developments of the invention are the subject of the dependent claims.

The solution of the invention is to use two pairs of coils, their Secondary signals compensate each other by sampling the Difference signal to detect electrically and magnetically conductive objects. For the Tripping is decisive that an end edge of the sensor coil pair with the electrically conductive objects fully or partially comes to cover from the Amplitude of the difference signal, the distance from the electrically conductive object derive the covered coil face.

With the tolerance of the switching distance, the distance traveled by the electrically conductive objects is also taken into account during a cycle time. If the cycle time for scanning the two pairs of coils is 1 ms and the approach speed is 1 km / h, a max. Switching distance errors of 0.28 mm occur. Aging tolerances of the components that influence the current pulse and the switching threshold of the comparator must also be taken into account.

When n distance ranges are recognized, the generated Differential signals provided at the output, in this case is only Clock generator, a pulse generator and a 'one-shot multivibrator' necessary. The two differential signals from two proximity switches can be connected in series be switched, it should be noted that a differential signal is positive and that other is negative. If both secondary signals are positive or negative, the  Lead the beginning of one secondary coil to the end of the other secondary coil. If the binary value of the amplitudes of the difference signals is to be transmitted, this is done an analog / digital conversion of the difference signals in a black box.

By means of a microcontroller or signal processor, the functionality of the Proximity switch can be increased significantly with fewer components. The Power MOSFET transistor that switches the current pulse can be directly from the Microcontrollers can be controlled. To eliminate interference after the Detection of the switching distance of the metallic object a current pulse sequence to be triggered. With an A / D converter or signal processor, the n Distance ranges via serial bus systems such as Profibus or CAN be passed on. The data can also be transmitted via radio. The designs are made in two, three and four wire technology in conjunction with programmable logic controllers. With the help of a non-volatile Memory in the proximity switch, z. B. two switching distances on site be programmed. The proximity switch is mechanically in the position brought, at which he should switch. After that, the level of a certain one Control line changed, the microcontroller is in programming mode and does not store the measured value of the amplitude of the difference signal in a volatile memory. Then the control line is changed Proximity switch is in operating mode, the microcontroller performs with everyone Query a comparison with the stored binary difference signal value through, when the switching distance is reached, the output power MOSFET transistor the external load.

The invention is described below with reference to the drawings of Embodiments of a precise inductive proximity switch with a and several switching distances explained in more detail, the two coil pairs with a primary coil and two secondary coils are designed to pass through the  Change of the difference signal by a metallic or magnetic object derive a function.

In the development according to protection claim 2, the two pairs of coils are formed with two primary coils and two secondary coils to pass through the Change of the difference signal by a metallic or magnetic object derive a function.

Show it:

Fig. 1A shows in section a schematic representation of a proximity switch in a metal housing, in which a primary coil and two secondary coils are integrated whose difference signal is damped by a metallic object that approaches radially, the two coil pairs together with the metallic object each as an open magnetic Circle are formed

FIG. 1B shows a sectional schematic illustration of a proximity switch in a metal housing, this is a primary coil and two secondary coils integrates the difference signal is attenuated by an on / off switch, wherein the two pairs of coils together with the metallic switch in each case designed as an open magnetic circuit are,

Fig. 1C illustrates a sectional schematic illustration of a proximity switch in a metal housing, in this two primary coils and two secondary coils are integrated whose difference signal is attenuated by a metallic object, which is always greater than a pair of coils, the two pairs of coils together with the metallic object, respectively are designed as an open magnetic circuit,

Fig. 1D illustrates a sectional schematic illustration of a relatively small proximity switch in a plastic housing, in which two primary coils and two secondary coils are integrated, the difference signal is increased by a Ferritstift, this is immersed in the sensor coil pair, thereby the possible switching distance increases. The increase in the switching distance can also be brought about by a shell core, the two coil pairs together with the magnetic object each being designed as a semi-open magnetic circuit,

Fig. 1E shows the representation of an inductance of a primary coil, and a current pulse flowing through the primary coil,

Fig. 1F shows a representation of an inductance of two primary coils, the primary coils are connected in series so that both magnetic fields are compensated, and a current pulse flowing through two primary coils,

Fig. 1G shows the representation of the inductances of two primary coils, the primary coils are connected in series so that the two magnetic fields did not compensate for this, and a current pulse flowing through the two primary coils,

Fig. 1H shows the representation of the inductances of two primary coils, the primary coils are connected in parallel, and displays a current pulse flowing through the two primary coils,

Fig. 1I shows the representation of a circular turn of a primary coil,

Fig. 1J shows the representation of a square coil of a primary coil,

Fig. 1K shows the representation of a metallic or magnetically conductive object,

Fig. 1L shows in section a schematic representation of a proximity switch in a metal housing, in this two primary coils and two secondary coils are integrated, taking place in the basic position an adjustment of the difference signal of the proximity switch by adjusting a winding to the manufacturing tolerances of the two pairs of coils to compensate,

Fig. 1M shows in section a schematic representation of a proximity switch in a metal housing, in this two pairs of coils are integrated, the difference signal is attenuated by a metallic object, this has the same configuration as the pairs of coils, the two pairs of coils together with the metallic object respectively as open magnetic circuit are formed,

Fig. 2A shows in section a schematic representation of a proximity switch in a truck in a metal housing, in this, two pairs of coils integrates the difference signal is attenuated by a metal guide track, said two pairs of coils together with the metallic guide track are in each case designed as an open magnetic circuit,

Fig. 2B shows a section of a schematic representation of two proximity switches in an industrial truck with n propriety areas each having a metal housing, in these two pairs of coils are respectively integrated, the secondary coils are highlighted, and the two differential signals are connected in series and damped by a metallic guide track , wherein one difference signal is positive and the other is negative, and the respective two coil pairs together with the metallic guide track are each designed as an open magnetic circuit.

Fig. 2C shows in section a schematic representation of a proximity switch with n propriety areas that are two axially arranged coil pairs integrates the difference signal is attenuated by a metallic object, wherein the two pairs of coils together with the metallic object are designed as an open magnetic circuit,

Fig. 2D shows in section a schematic representation of a proximity switch, in this two pairs of coils are integrated, the magnetic field is increased by a magnetic object, wherein the two pairs of coils together with the magnetic object are formed as semi-open magnetic circuit,

Fig. 2E shows a diagram of a metal guide track, this is laid on a roadway,

Fig. 2F illustrates a sectional view of a proximity switch, having two coil bodies and two pairs of coils, wherein the sensor coil pair is addressed to a metallic object approaching axially, a control plate with an adjustable resistor for adjusting the switching distance, a display of the sensing distance by means of a LED and a comparison of the difference signal, the proximity switch being protected by a metal housing,

Fig. 3A shows a basic circuit diagram of a proximity switch, a clock generator and current pulse switch generate a pulse of current flowing through a primary coil of the two coil pairs, the difference signal of the two secondary coils is evaluated by a control logic, being triggered by a metallic object a switching distance around a load to switch,

Fig. 3B shows a timing diagram with a representation of a clock line, a current pulse, a difference signal and a switching process,

Fig. 3C shows the symbol of the n-switching proximity switch in three-wire technology,

Fig. 3D shows a basic circuit diagram of a proximity switch, a clock generator, a 'one-shot multivibrator' and a switch, a current pulse is generated which flows through a primary coil of the two coil pairs, the difference signal of the two secondary coils is provided at the output, n distance areas can be triggered by a metallic object, these are evaluated in a black box,

Fig. 3E shows a timing diagram with a representation of a clock line, a current pulse of a differential signal and a strobe line, device for an accurate inductive proximity switch according to the embodiment of FIG. 1A illustrates a sectional schematic illustration of a proximity switch (1) with a metal housing (10 ), wherein the two pairs of coils (2, are each formed 3) together with the metallic object (9/1), as an open magnetic circuit. Both pairs of coils ( 2 , 3 ) are arranged axially one above the other and are so far apart from one another that little or no mutual interference is possible. The metallic object (9/1), is removed as much of the pair of coils (2) that there is no attenuation of the difference signal (22) is possible. The coil pair (2) is formed by the coils (311, 2/2), the sensor coil pair (3) is formed by the coils (3/1, 3/2). The primary coil (3/1), is centrally and axially to the two secondary coils (2/2 3/2). In a magnetic excitation current pulse (21) flows from the coil terminal (4/1), via the primary coil (3/1), to the coil terminal (4/2). Characterized is inductively coupled from the primary coil (3/1) into the secondary coil (2/2, 3/2), two secondary signals. At the coil terminals (5/1 5/3), the positive secondary signal of the secondary coil (2/2) stands on the other hand, is at the coil terminals (5/2, 5/3) to the negative secondary signal of the secondary winding (3/2) . The secondary coils (2/2, 3/2) are connected in series so that the secondary signals cancel each other when no metallic object (9/1), can damp the sensor coil pair (3). In the basic position, the difference signal (22) is now (9/1), covered at the coil terminals (5/1 5/2) the voltage value of 0 V. If by a metallic object through a radial approach the face of the sensor coil pair (3) producing pairs of coils (2, 3) at the coil connections (5/1 5/2) a difference signal (22), it may be positive or negative. The polarity of the difference signal ( 22 ) depends on whether the sensor coil pair ( 3 ) or the coil pair ( 2 ) is covered by a metallic object; in the exemplary embodiment, a positive difference signal is generated here. Device for an accurate inductive proximity switch according to the embodiment of FIG. 1B shows a sectional schematic illustration of a proximity switch (1/1) with a metal housing (10), wherein the two pairs of coils (2, 3) together with the metallic object (9 / 2 ) are each designed as an open magnetic circuit. If now by a metallic object (9/2), which is formed here by an on / off switch, covering the end face of the sensor coil pair (3), which generate pairs of coils (2, 3) at the coil connections (5/1, 5 / 2 ) a positive difference signal ( 22 ).

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1C illustrates a sectional schematic illustration of a proximity switch (1/2) with a metal housing (10), wherein the two pairs of coils (2, 3) together with the metallic object (9 / 3 ) are each designed as an open magnetic circuit. In this embodiment, the coil terminal (5/1) leads to the start of the secondary coil (2/2), the end of which is connected to the start of the secondary coil (3/2) is connected to the coil terminal (5/3) and whose end leads to the coil terminal (5/2). In a magnetic excitation current pulse (21) from the beginning of the coil terminal (4/1), flows (2/1), the end of which leads through the primary coil to the end of the primary coil (3/1), and its top on the coil terminal (4/2). Thereby be inductively coupled (2/2, 3/2), two secondary signals in the secondary coils by the primary coils (2/1, 3/1). At the coil terminals (5/1 5/3), the positive secondary signal of the secondary coil (2/2) stands on the other hand, is at the coil terminals (5/2, 5/3) to the negative secondary signal of the secondary winding (3/2) . The coil pairs ( 2 , 3 ) are connected in series so that the secondary signals compensate each other when no metallic object ( 913 ) can dampen the sensor coil pair ( 3 ). In the basic position has the difference signal (22), which is tapped at the coil terminals (5/1 5/2), the voltage value of 0 V. If now by a metallic object (9/3), the end face of the sensor coil pair (3) covered in the axial direction, generate the pairs of coils (2, 3) at the coil connections (5/1 5/2) a positive difference signal (22). In order to stabilize the differential signal (22) is reduced by means of a cover (10/1). The metallic object (9/3) is greater than a coil pair and can, for. B. be a circuit board whose copper layer thickness is to be determined. With a distinction of the thickness of 18 μ, 35 μ and 70 μ, three switch distances are required for the evaluation of the difference signal ( 22 ), which are formed by the expansion of the basic circuit according to FIG. ( 3 A) by means of two additional operational amplifiers, two flip-flops , two trimming resistors and two light emitting diodes, whereby the highest value of the 'thick display' is valid. With this arrangement, a crack in a weld seam or a type of metal can also be determined if the thickness of the metal is constant. If the type of metal is always the same, z. B. also the thickness of a metallic foil can be measured.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1D illustrates a sectional schematic illustration of a relatively small proximity switch (1/3), with a plastic housing (10), wherein the two pairs of coils (2, 3) together with the metallic object (9/4) are each formed as a half-open magnetic circuit. The magnetic object (9/4) is used to increase the operating distance and is a Ferritstift, this is immersed in the sensor coil pair in the axial direction. When the pair of coils (2) of the proximity switch (1/3), the secondary coil (2/2) the inner layer and the primary coil (2/1), the outer layer, the sensor coil pair (3) is the secondary coil (3/2) the inner layer and the primary spool (3/1), the outer layer, wherein the function of both pairs of coils (2, 3) are fully retained. Depending on the evaluation of the difference signal (22) 3A is an operating distance or more operating distances can according to the principle circuit shown in FIG. Be determined because the difference signal (22) increases continuously during an approach of the Ferritstifts (9/4). The increase of the switching distance can also be effected by one or two pot-type cores (8/2) of high permeability ferrite material, the air distance to metallic object is reduced by the shell core. The inductance increases, the shell core forms the magnetic field of the coil. According to the principle circuit shown in FIG. 3D n pitch regions can be identified because the difference signal (22) is provided at the output in order to evaluate it according to a specification of the user in a black box. A plastic housing is used here because no metallic foreign objects can change the differential signal.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1E shows a primary coil (3/1), whose initial leads to the coil terminal (4/1), the end of this winding leads to the coil terminal (4/2), which function is retained when the beginning of the primary coil (3/1), reversed at the end.

Device for an accurate inductive proximity switch according to the embodiment of Fig. 1F shows two primary coils (2/1, 3/1). The two fields of these primary coils (2/1, 3/1) cancel each other out when a current pulse (21) flows, because the coil terminal (4/1), to the beginning of the coil wire of the primary coil (2/1), leads the end of this winding leads to the end of the coil wire of the primary coil (3/1), the beginning of this winding coil terminal leads (4/2). With this arrangement, the magnetic field does not affect other components.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1G shows two primary coils (2/1, 3/1). The two fields of these primary coils (2/1, 3/1), do not cancel when a current pulse (21) flows, because the coil terminal (4/1), leads to the beginning of the coil wire of the primary coil (2/1), the end of this winding leads to the beginning of the coil wire of the primary coil (3/1), the end of this winding coil terminal leads (4/2), which function is retained.

Device for an accurate inductive proximity switch according to the embodiment of Fig. 1H depicts two primary coils (2/1, 3/1) which are connected in parallel, and lead the ends of the coil terminals (4/1, 4/2). The current pulse ( 21 ) divides, it is not ensured that both partial currents have the same amplitude, the function of the coil pairs ( 2 , 3 ) is retained because both coil pairs are switched so that both secondary signals compensate. If the start and end of each coil pair ( 2 , 3 ) are connected in parallel, the magnetic fields cancel each other out.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1I shows a circular turn of a primary coil (2/1), with the diameter D through which a current pulse (21) flows. As a rule, the formation of one turn of the pair of coils ( 2 , 3 ) is the same, the function is retained even with different designs.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1J shows one turn of a primary coil (2/1), with side length D, through the winding, a current pulse (21), whose field strength is higher because the wire length of the coil is greater . In the device for a precise inductive proximity switch, the formation of a turn of the coil pair ( 2 , 3 ) can be as desired.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1C shows a metallic or magnetic object (9/5), the formation may be any, at a variable thickness.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1L shows a proximity switch (1/4) with two pairs of coils (2, 3), these consist of four windings (2/1, 2/2, 3/1, 3 / 2 ). The adjustment of the differential signal (22) to the voltage value 0 V is carried out in the basic position by the adjusting of the coil (2/2) in the axial direction. The function is preserved when the coil (2/1), is adjusted. In the embodiment of the bobbin winding has (2/1), a pin on which the bobbin of the winding is guided in the axial direction (2/2), after the adjustment of the difference signal to the voltage value of 0 volt permanent fixation is carried out of the coil ( 2/2).

Device for an accurate inductive proximity switch according to the embodiment of FIG. 1M, shows in section a schematic representation of a proximity switch (1/5) with a metal housing (10), wherein the two pairs of coils (2, 3) together with the metallic object (9 / 6 ) are each designed as an open magnetic circuit. The pairs of coils (2, 3) are arranged side by side here that the sensor coil pair (3) is directed to the metallic object (9/6). When the pair of coils (2) the primary coil (211) is the inner layer and the secondary coil (2/2), the outer layer. In the sensor coil pair (3), the primary coil (3 / l), the inner layer and the secondary coil (3/2), the backsheet, wherein the function of both pairs of coils (2, 3) are fully retained. In order to stabilize the differential signal is reduced by means of a cover (10/2), the metallic object (9/6) here has the same configuration as the pairs of coils (2, 3). The pairs of coils (2, 3) have the shape of a triangle together with the metallic object (9/6). The exact position and angle of rotation of a triangle ( 916 ) is recognized by the coil pairs ( 2 , 3 ). For a given material thickness of the object (9/6) the difference signal (22) reaches the max. possible value, if the triangle (9/6) with the pair of coils (2, 3) is completely congruent.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 2A shows in section a schematic representation of a proximity switch (1/6) in an industrial truck with a metal housing (10), wherein the two pairs of coils (2, 3) together with the metallic object (9/7) are each designed as an open magnetic circuit. The metallic object is a guide track (9/7), this is laid under a floor covering and has the task to perform a truck in the track. The ground clearance B of the proximity switch to the guide track changes only slightly. The proximity switch (1/6) scans the guide track (9/7) down through the two pairs of coils (2, 3). Is the difference signal (22) is nearly 0 V because the two pairs of coils (2, 3) does not come more to cover by the guide track (9/7), both drive motors are switched off to stop the truck.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 2B shows a section of a schematic representation of two proximity switch (1/7, 1/8) with a metal housing (10), the secondary coils (2/2, 3/2) of proximity switch (1/7) and the secondary coil (2/2, 3/2) of the proximity switch (1/8), wherein the respective pairs of coils (2, 3) (9/8) in each case designed as an open magnetic circuit together with the metallic object are. The two proximity switches (1/7, 1/8) are arranged in an industrial truck such that viewed in the direction of travel adjacent to each other, so, by the difference signal (22/1, 22/2) represented by the difference signals (22 ) of both proximity switches (1/7 1/8 is formed), the position of the center of the guide track (9/8) are determined of the truck. The metallic object is a guide track (9/8), it is laid on the roadway and has the task to perform a truck in the track. Because the secondary coil (3/2) (/ 1 7) of the proximity switch directed to the guide track, a positive here difference signal is generated. When the proximity switch (1/8) the secondary coil (2/2) is directed to the guide track, so negative differential signal (22) is generated here. The secondary coils (2/2, 3/2) of the proximity switch (1/7) are connected with the secondary coil (2/2, 3/2) of the proximity switch (1/8) in series so that at the output of the difference signal (22 / 1, 22/2) is available at the output. If the guide track in the middle of the two proximity switches (1/7, 1/8), so the difference signals (22) are equal in amplitude high but different in polarity, so that they compensate each other, and at the output of the difference signal (22/1, 22/2) is available. If the truck is to the far right of the guide track (9/8), the difference signal (22) is arranged on the left of the proximity switch (1/7) higher, so that a positive difference signal (22) is formed. The position of the truck to the guide track (9/8) is derived from the polarity of negative or positive.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 2C shows in section a schematic representation of a proximity switch (1/9), wherein the two pairs of coils (2, 3) together with the metallic object (9/9) respectively as an open magnetic Circle are formed. The difference signal (22) may be, in the basic position, the voltage value 0 volts, with the aid of the proximity switch (1/9). B. a metallic object can be located in the ground because this increases the difference signal ( 22 ).

Device for an accurate inductive proximity switch according to the embodiment of FIG. 2D illustrates a sectional schematic illustration of a proximity switch (1/10) in a metal housing (10), wherein the two pairs of coils (2, 3) together with the magnetic object in each case as semi-open magnetic circuit are formed. The coil pair ( 2 ) is arranged perpendicular to the sensor coil pair ( 3 ), the function is still retained because the two coil pairs ( 2 , 3 ) are connected in series so that the two secondary signals compensate each other. The magnetic object is not shown, because it can have any form, by means of the proximity switch (1/10) of the switching distance can be increased.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 2E shows a metallic object a guide track (9/11) of a stainless spring steel strip, whose thickness and width is variable, the two pairs of coils can be damped by a metallic sheet, an aluminum sheet is very suitable for this.

Device for an accurate inductive proximity switch according to the embodiment of FIG. 2F illustrates a sectional view of a proximity switch (1/11) with a metal housing (10), two coil bobbins (8, 8/1), a pair of coils (2) and (3 ), a winding space (6/5), a control plate (6), a sensing distance adjustment (6/1), a display of the switching distance (6/2), a comparison of the difference signal (6/6), two fastening nuts (7 , 7/1), a housing cover (10/4), a connecting cable (10/5), a cable gland (10/3) and a metallic object (9/12), which passes axially, whereby on the bobbin (8 wound), the winding of the secondary coil (2/2) and the sensor coil pair (3), wherein the winding of the primary coil is wound (2/1), on the coil former (8/1), wherein the remote pair of coils (2) from the coils (2/1 2/2), wherein the Sensorspulenp aar consists of the coils (3/1, 3/2), and wherein the pairs of coils (2, 3) are respectively formed together with the metallic object (9/12) as an open magnetic circuit. The housing (10) is provided with an external thread and, like the housing cover (10/4) of an electrically conductive material. To the capacity of the primary winding to minimize the secondary winding (312) (3/1), is a free space (6/5), the z between both windings. B. results from several insulating layers. Thus, the distance of the winding of the sensor coil pair (3) can be kept as low as possible to the metallic object (9/12), one side serves the bobbin (8) and housing wall. The coil body (8) forms with the coil pair (3) and the secondary coil (2/2) a unit, this has the advantage that the position of the two pairs of coils (2, 3) to each other of only by the balance (6/6) can change the bobbin (8/1). The difference signal (22) is aligned in the basic position, in which the axial position of the bobbin (8/1) to the primary coil (2/1) is variable by the adjustment (6/6). By an adjustable resistor (6/1), on the control panel (6) setting the switching distance, the state of the switching distance is carried out a light emitting diode (6/2) is slow displayed, which is visible from the outside from all sides. Thus, the switching distance deviates only slightly, only a certain object (9/12) should be used. When mounting of the proximity switch (1/11) Note that the usual clearances are maintained for proximity switches. The fastening of the proximity switch by two nuts (7, 7/1). A permanent fixation of the coils and the control plate ( 6 ) is carried out by a casting resin, so that the functionality is fully maintained in the event of shock and vibration. The proximity switch (1/11) is one embodiment, other mechanical structure may well prove to be expedient also to the difference signal (22) can be adjusted by other means. The adaptation to a specific task is first carried out by the size of the diameter of the coil pair ( 2 , 3 ) and the place of use. With minimal requirements of the proximity switch has (1/11) the degree of protection IP00, at the highest requirements is a proximity switch (1/11) with the degree of protection IP68 used. Instead of a shielded connecting cable (10/5), a plug connection can serve as an interface, the messages of the operating distances can also be transmitted wirelessly by radio.

The device for a precise inductive proximity switch, according to the basic circuit according to FIGS. 3A, 3B, represents a control logic for deriving a switching distance by means of two pairs of coils ( 2 , 3 ) and switching an external load (R24) on or off. The control logic essentially consists of a clock generator (15) a pulse generator (20), an operational amplifier (33), a flip-flop (35), a power MOSFET (T4), a Schaltabstands- balance (6/1) by means of the variable resistor R8, and a display of the switching interval (6/2). The voltage peaks of the operating voltage ( 44 ) are smoothed by means of the capacitors C8 and C9. The primary coil (3/1) is magnetically energized to turn by a metallic object (9/1), an external load (R24). The positive operating voltage is supplied through line ( 44 ), line ( 46 ) GND has the potential of 0 volts. An external load R24 is connected to the operating voltage ( 44 ) and the connecting line ( 45 ). In a proximity switch, two pairs of coils (2, 3) having a primary coil (3/1), and the secondary coils (2/2, 3/2) arranged such that the primary coil (3/1) between the two secondary windings (2/2 , 3/2) arranged in the axial direction and the end side of the secondary coil (/ 3 directed 2) to a metallic object (9/1). One of incorrect lubricant of the secondary coils (2/2, 3/2) results in no impairment, except that here a negative difference signal (22) is generated. In the embodiment, a positive difference signal (22) is generated by the control logic, since the sensor coil pair (3) (9/1) comes with a metallic object is intended to cover.

The coil terminal (4/1), leads to the beginning of the primary coil (3/1), the end of the primary coil (3/1), leads to the coil terminal (4/2). The coil terminal (5/1) leads to the start of the secondary coil (2/2), the end of which leads to the coil terminal (5/3) and connects the end of the secondary coil (3/2) whose initial leads to the coil terminal 5/2. Since the beginning and end of both secondary coils (2/2, 3/2) are reversed, is connected to the coil terminals (5/1 5/2) only the difference signal (22) of the two secondary signals of the secondary coils (2/2, 3/2 ) effective when a current pulse ( 21 ) is triggered by the pulse generator ( 15 ). Through the primary winding (3/1), a current pulse (21) flows from the coil terminal (4/1), to the coil terminal (4/2), characterized to be from the primary coil (3/1) into the secondary coil (2/2, 3/2 ) two secondary signals inductively coupled. At the coil terminals (5/1 5/3), the positive secondary signal of the secondary coil (2/2) stands on the other hand, is at the coil terminals (5/2, 5/3) to the negative secondary signal of the secondary coil (3/2) . Depending on whether the end faces of the coil pair (3) are covered by a metallic object (9/1), which produce secondary coils (2/2, 3/2) to the coil terminals (5/1 5/2) no difference signal ( 22 ), or a positive difference signal ( 22 ). The secondary coils (2/2, 3/2) supplied to the coil terminals (5/1 5/2) no difference signal (22) or only a slight difference signal (22) when no metallic object (9/1), the sensor coil pair ( 3 ) covered. The secondary coils (2/2, 3/2) supplied to the coil terminals (5/1 5/2) to the highest possible value of a positive difference signal (22) when a very good electrically conductive object (9/1), the end face of Sensor coil pairs ( 3 ) covered completely and without switching distance.

The clock generator ( 15 ) is designed according to a conventional circuit and consists of an inverter, the RC element R1 C1, the resistors R2, R3, and a diode D2. After switching on the operating voltage, the clock generator ( 15 ) is ready for operation, so that the clock line ( 19 ) cyclically generates a positive pulse of approximately 20 microseconds and a negative pulse of approximately 1 ms, the clock line ( 47 ) is inverted. The duty cycle of the clock generator ( 15 ) can be changed by changing the resistor R3, the cycle time of the clock line ( 19 ) is determined by the RC element R1 and C1, the adjustment of the cycle time is done by changing the resistance of R2. At a high rate of approach of a metallic object (9/1), the cycle time of the clock generator (15) must be decreased, the resistance value of R1 is lowered.

The pulse generator ( 20 ) consists of a power MOSFET transistor T1 and an RC element R5 and C3, a diode D1, an RC element R4 and C2, this RC element rounds off the rising edge of the current pulse ( 21 ). The diode D1 on the coil terminal (4/1), is to limit the negative primary signal the task. Resistor R5 is connected to the operating voltage via line ( 44 ). During the time when the clock line ( 19 ) has a low level, the power MOSFET transistor T1 is blocked and the capacitor C3 is charged via the resistor R5. The charging time is terminated when (4/1), is present, the amplitude of the operating voltage (44) on the coil terminal. The current pulse ( 21 ) is triggered with a high level of the clock line ( 19 ) in that the voltage rises continuously via the RC element R4 and C2 and finally the power MOSFET transistor T1 switches, and the capacitor C3 switches over the primary coil ( 3/1) and the drain Sourse path can discharge the power MOSFET transistor T1. By the current pulse (21) a secondary signal in the secondary coils is at the rising edge and falling edge, respectively (2/2, 3/2) inductively coupled, which as the difference at the coil terminals (5/1 5/2) as a difference signal (22 ) pending.

In the exemplary embodiment, the difference signal ( 22 ) that arises on the leading edge of the current pulse ( 21 ) is evaluated.

The terminating resistor R6 is connected to the coil terminals (5/1 5/2) and causes an additional interference protection of the differential signal (22). On the coil terminal (5/2), the difference signal (22) is short-circuited at one end by the capacitor C4 alternating current to the operating voltage (44). The resistance ratio of the resistors R7 + R8 R9 determines the potential on the coil terminal (5/2), the potential here has half the operating voltage (44). The operating distance (6/1) is set by R8, resistors R22 and R23 are used to produce a hysteresis, and are carried out by a conventional circuit only when the difference signal (22) is higher than the voltage drop across R8 plus the voltage value by the Hysteresis, the operational amplifier ( 33 ) can briefly switch the line ( 34 ) to almost 0 volts. The operating voltage of the line ( 44 ) serves as an operating voltage supply for the CMOS modules and the external load (R24). The RC element R17 and C5 is connected via the line ( 40 ) to an input of the flip-flop ( 35 ). The operating voltage ( 44 ) is supplied via the resistor R17. The capacitor C5 is charged when the operating voltage ( 44 ) is switched on, and as a result the voltage on the line ( 40 ) increases until the capacitor C5 is charged. During this time there is a short low pulse and resets the flip-flop ( 35 ) to the basic position. The line (37) goes to a high level, the display (6/2) of the switching distance is turned off via the control line (37). At the same time the line ( 36 ) changes to a low level, so that the power MOSFET transistor T4 is blocked and the external load (R24) is switched off via the control line ( 45 ). The input of the flip-flop ( 35 ) is kept at a high level via the line ( 34 ) via the resistor R15.

In order to trigger a switching function at a certain threshold of a positive difference signal ( 22 ), the difference signal ( 22 ) is fed to the input of the operational amplifier ( 33 ). A positive reference voltage is present at the + input of the operational amplifier ( 33 ). This voltage is generated by the current through the resistor R8 and the hysteresis of the OP ( 33 ). Is the positive difference signal z. B. + 300 mV, the value of R8 is determined so that the voltage drop across R8 and the hysteresis of the OP is approximately 270 mV. If the amplitude of the positive difference signal ( 22 ) exceeds this value, the operational amplifier ( 33 ) switches. Because the pulse width of the differential signal ( 22 ) is small, a short low pulse occurs when the operational amplifier ( 33 ) is switched at the output ( 36 ). The line ( 34 ) connects the output of the operational amplifier ( 33 ) to the input of the flip-flop ( 35 ), so that the flip-flop ( 35 ) is set with a short low pulse. The control line ( 36 ) of the flip-flop ( 35 ) leads to the gate connection of the power MOSFET transistor T4. If the flip-flop ( 35 ) is set, the control line ( 36 ) is switched to a high level, the power MOSFET transistor T4 becomes conductive, and the external load R24 is switched on. Simultaneously, the 'on-state' of the switching distance of the control line (37) and the display of the switching distance (6/2) is displayed by the control line (37) switches to a low level, and the operating voltage (44) and the resistor R20 and the light emitting diode (6/2) and control line (37) and a current can flow through the output of the flip-flop (36) which is limited by the resistor R20.

Let us now assume that the operating voltage ( 44 ) of the proximity switch is switched on. Capacitor C5 is charged and thereby the voltage on line ( 40 ) rises until capacitor C5 is charged. During this time, a short low pulse occurs and resets the flip-flop ( 35 ) to the basic position. The line (37) is maintained at a high level, so that the light-emitting diode (6/2) is switched off, simultaneously the line (36) changes to a low level so that the power MOSFET transistor T4 is blocked and the external load (R24) is switched off via the control line ( 45 ).

Now assume the case that the clock line ( 19 ) switches from a high level to a low level, the power MOSFET transistor T1 of the pulse generator ( 20 ) is blocked, so that the capacitor C3 via the operating voltage ( 44 ) and the resistor R5 is charged. The charging process is complete when the capacitor C3 has reached the amplitude of the operating voltage (44) on the coil terminal (4/1).

Now assume the case that the clock line ( 19 ) switches from a low level to a high level, two different functions are effected simultaneously, the flip-flop ( 35 ) is brought into the basic position and a current pulse ( 21 ) is caused. The flip-flop ( 35 ) is brought into the basic position by the inverted clock line ( 47 ), an inverter, an RC element R21 and C6, a further inverter, a resistor R16, so that a very short low pulse is generated , which is present at the line ( 39 ), the resistor R16, and the input of the flip-flop ( 35 ), so that the control line ( 36 ) switches to a low level, the power MOSFET transistor T1 is briefly switched off. In this embodiment, this has no meaning. At the same time line (37) changes to a high level, so that the light-emitting diode (6/2) is turned off. Now, the case is assumed that a current pulse (21) is triggered, in which the power MOSFET transistor of the pulse generator (20) T1 becomes conductive so that the capacitor C3 can be discharged through the primary coil (3/1), namely a current pulse (21) from the capacitor C3 through the coil terminal (4/1), the primary coil (3/1) through the inductor (3/1), via the coil terminal (4/2) via the conducting transistor T1 to the ground terminal of the Capacitor C3. Are the end faces of the sensor coil pair (3) completely free of an electrically or magnetically conductive object (9/1), then induced by an inductive coupling in the secondary coils (2/2, 3/2) two identical secondary signals mutually compensate, and their difference is the difference signal (22) at the coil terminals (5/1 5/2) are available. The difference signal ( 22 ) has the voltage value of 0 volts or is very low, this is fed to the input of the operational amplifier ( 33 ), and because it is so low, the operational amplifier ( 33 ) cannot switch and the control line ( 36 ) remains on one Low level, the external load R24 is still switched off.

Now, the case is assumed that the sensor coil pair (3) a metallic object (9/1), passes, so the difference signal (22) rises steadily, which is present at the input of the operational amplifier (33), and because the amplitude of the differential signal ( 22 ) is higher than the voltage drop across the resistor R8 and the hysteresis, the operational amplifier ( 33 ) switches the line ( 34 ) with a short low pulse, the flip-flop ( 35 ) is set, and the control line ( 36 ) opens a high level, the power MOSFET transistor T4 becomes conductive and the external load R24 is switched on via the control line ( 45 ). Simultaneously, the control line (37) goes to a low level, and the light-emitting diode (6/2) is switched on via the control line (37).

The pulse generator ( 20 ) is triggered cyclically by the clock generator, so that a differential signal ( 22 ) is in turn generated by the next current pulse ( 21 ). If the difference signal ( 22 ) is less than the voltage drop at R8 plus the voltage value due to the hysteresis, the operational amplifier ( 33 ) can no longer switch the line ( 34 ) to 0 volts and the flip-flop ( 35 ) can therefore not be set become. The flip-flop ( 35 ) remains in the basic position, so that the control line ( 36 ) remains at a low level, and the power MOSFET transistor T1, the load R24 is further switched off via the line ( 45 ). The line (37) remains at a high level, so that the light-emitting diode (6/2) is further turned off.

For the sake of simplicity, a proximity switch is listed here with a switching distance that is not programmable and whose operating voltage and output switch are not protected against reverse polarity. The programmability relates to the switch type n-switching or p-switching and to the automatic setting of the switching distance on site. If several or two switching distances are necessary, the basic circuit according to FIG. 3A is supplemented by means of an operational amplifier, a flip-flop, a power MOSFET, a switching distance adjustment by means of an adjustable resistor, and an LED for displaying the switching distance. The basic circuit of Fig. 3A performs only a pair of coils (2, 3) displayed on a primary coil, the variants of the embodiments of the pairs of coils (2, 3) are substantially of FIG. 1n and Fig. 2n.

The device for a precise inductive proximity switch, according to the circuit symbol according to FIG. 3C, shows the exemplary embodiment of an n-switching proximity switch in three-wire technology, the usual protective circuits are integrated here. The proximity switch has reverse polarity protection and is also protected against overload and short circuit, after the overload has been removed it is functional again. Protective diodes for switching inductive loads are also installed. By programming it can be changed from an n-switching type to a p-switching type. The operating voltage is 20 V to 260 V DC, in one variant the operating voltage is 20 V to 240 V AC, with a temperature range from -25 ° C to + 80 ° C, the connecting cable is shielded.

The device for a precise inductive proximity switch, according to the basic circuit according to FIGS. 3D and 3E, represents a basic circuit of a control logic in order to determine the difference signals ( 22 ) by means of two pairs of coils ( 2 , 3 ), which are arranged in a proximity switch ( 1 ) in a black box ( 49 ) to evaluate z. B. n spacer regions by the metallic object (9/1), to be recognized. The control logic consists of a clock generator ( 15 ), a pulse generator ( 20 ), a 'one-shot multivibrators' ( 55 ) and a black box ( 49 ), in which the difference signal ( 22 ) is evaluated by the user in order to derive a specific function . The conclusion of the difference signal (22) is made by the terminating resistor R6 via the twisted pair (10/5) in the black box (49). The basic circuit of the clock generator ( 15 ) and the pulse generator ( 20 ) is identical to the basic circuit according to FIG. 3A, an explanation is therefore omitted. In contrast to this, a strobe line ( 48 ) is derived from the falling edge of the clock line ( 47 ) in order to increase the max. Amplitude of the differential signal (22, 5/2) to determine in a black box (49). The usual 'one-shot multivibrator' ( 55 ) consists of an operational amplifier ( 54 ), the resistors R50 to R52, the capacitors C6 and C7 and the diodes D3 and D4. The pulse width is determined by the capacitor C7 and the adjustable resistor R52. If a current pulse ( 21 ) is triggered, the edge of the clock line ( 19 ) changes from low to high beforehand, the clock line ( 47 ) is inverted, this edge changes from high to low. At this time, a pulse is generated via the capacitor C6, which is present at the input of the operational amplifier ( 54 ). The RC element R51 and C7 generates a positive strobe pulse at the output of the operational amplifier ( 54 ), which leads via the strobe line ( 48 ) to the black box ( 49 ). The pulse width of the strobe pulse is set by the adjustable resistor R52, the diodes D3 and D4 limit the negative voltage. By means of two proximity switches (1/7, 1/8) of Fig. 2B is z. B. guided an industrial truck on a guide track. Two pairs of coils ( 2 , 3 ) are connected in series, the phase shift of both difference signals ( 22 ) may only be slight. In a radial approach at a constant ground clearance B can to the metal guide track (9/8), the cover measured by the guide track (9/8) to z. B. derive the deviation from the center of the guide track (9/8). A very high stability of the clock generator ( 15 ), the pulse generator ( 20 ) and the 'one-shot multivibrator' ( 55 ) is required here. In an axial approach of the object (9/1), z can. B. measure the exact distance to the metal object (9/1). The basic circuit is also suitable for the arrangement of the pairs of coils (2, 3) according to Fig. 2C, 2D, in which the metallic objects (9/9, 9/10) are at rest, and the coil pairs (2, 3) in X / Y direction can be moved to e.g. As to locate the metallic objects (9/9, 9/10). In the black box ( 49 ) the difference signal ( 22 ) is taken over by the high / low edge of the strobe line ( 48 ). The evaluation of the difference signal ( 22 ) takes place, for. B. by an AID converter. At the time of the high / low edge of the strobe line ( 48 ), the analog difference signal ( 22 ) is converted into a digital value. Because the secondary coil (3/2) (/ 1 7) of the proximity switch directed to the guide track, a positive here difference signal is generated.

Claims (30)

1.Device for a precise inductive proximity switch with a large switching distance, two pairs of coils being provided for inductive coupling, the end faces of which are each axially aligned with the electrically or magnetically conductive objects and two voltages are induced in the two secondary coils when the primary coil is energized, whose difference the control logic evaluates to identify the switching distances, the two pairs of coils, together with the electrically conductive object, are each designed as an open magnetic circuit, the metallic objects of which are designed to be electrically conductive, so as to cover an increasing damping of the induced voltage in to effect the secondary winding of a pair of coils, characterized in that

• - that the primary coil (3/1), and the secondary windings (2/2, 3/2) of each coil pair (2, 3) are arranged one above the other,
• - that the pairs of coils (2, 3) are formed together with the metallic object (9/1), as an open magnetic circuit, and
• - that the metallic object (9/1), is electrically conductive to give (3/2) to effect at a registration with the end face of the coil pair (3) increasing the damping of the induced voltage in the secondary winding of the coil pair (3).

2. Device according to claim 1, characterized in that means are provided for inductive coupling of the coil pairs (2, 3) comprises two primary coils and two secondary coils that only one pair of coils (3) (9/3) comes through the object to cover and remote from Coil pair ( 2 ) is arranged in any X / Y / Z position relative to the coil pair ( 3 ), 3. Apparatus according to claim 1 and 2, characterized in that the identification of an electrically conductive object or magnetically conductive object is derived from the polarity of the difference signal ( 22 ). 4. The device according to claim 1 and 2, characterized in that a switching distance of the proximity switch (1/11) (9/12) triggers by means of a metallic object has a particular function. 5. Device according to claim 1 and 2, characterized in that n distance ranges are determined to the metallic object (9/12). 6. Apparatus according to claim 1 and 2, characterized in that one or several switching distances can be programmed on site. 7. The device according to claim 1 and 2, characterized in that the Switch T4 is programmed to n-switching or p-switching. 8. Apparatus according to claim 1 and 2, characterized in that the formation of the coil pairs ( 2 , 3 ) is arbitrary. 9. Apparatus according to claim 1 and 2, characterized in that the formation of the metallic objects (9/1, 9 / n) is arbitrary. 10. Apparatus according to claim 1 and 2, characterized in that the formation of magnetically conductive objects (9/4) is arbitrary. 11. Apparatus according to claim 1 and 2, characterized in that the primary coils (2/1, 3/1) are connected in series. 12. The device according to claim 1 and 2, characterized in that the primary coils (2/1, 3/1) are connected in parallel. 13. Apparatus according to claim 1 and 2, characterized in that a proximity switch (1/1) a metallic object (9/2) identified, wherein said metallic object (9/2) is formed as an on / off switch. 14. The device according to claim 1 and 2, characterized in that the pair of coils (2, 3) of the proximity switch (1/2) is covered completely and at a certain distance by a metallic object (9/3) to the thickness of the metallic object (9/3) determine. 15. The device according to claim 1 and 2, characterized in that the shape of the end faces of the pair of coils (2, 3) of the proximity switch (1/5) are formed as the metallic object (9/6), the position and the angle of rotation of the metallic object (9/6) determine. 16. The apparatus of claim 1 and 2, characterized in that the bouncing of the switch T4 is prevented by a hysteresis of the operational amplifier ( 33 ). 17. The apparatus of claim 1 and 2, characterized in that the selection of the current generator ( 20 ) is carried out by a microcontroller. 18. The apparatus according to claim 1 and 2, characterized in that the current generator ( 20 ) generates a sine current pulse. 19. The apparatus according to claim 21, characterized in that the cycle time of the query is reduced when a metallic object ( 9 / n) is detected. 20. The apparatus according to claim 21, characterized in that the amplitudes of the differential signals ( 22 ) are transmitted by radio. 21. The apparatus according to claim 1 and 2, characterized in that the Output switch T4 as a two-wire, three-wire or four-wire switch is performed. 22. The apparatus of claim 1 and 2, characterized in that the output ( 45 ) and the operating voltage ( 44 , 46 ) is protected against reverse polarity. 23. The device according to claim 1 and 2, characterized in that a Proximity switch identifies a metallic object, the metallic one Object is designed as a bar code. 24. The device according to claim 1 and 2, characterized in that a proximity switch (1, 6) has a guide track (9/7) identified by the two drive motors off of the truck immediately when no guide track (9/7) was identified. 25. The device according to claim 1 and 2, characterized in that two proximity switches (1, 7, 1/8) sense a guide track (9/8), to lead to an industrial truck in an electroless real guide track (9/8), wherein both difference signals (22) have the same polarity, but the secondary windings (3/2) connected in series so that they compensate each other. 26. The apparatus according to claim 1, characterized in that the difference signal ( 22 ) is fed to a black box ( 49 ) in order to realize a specific function. 27. The device according to claim 1 and 2, characterized in that the manufacturing tolerances of the coil pair (2, 3) are offset by an adjustable resistor (6/1). 28. The device according to claim 1 and 2, characterized in that the pair of coils (2, 3) comprises four single coils (2/1 2/2, 3/1, 3/2), and the manufacturing tolerances by adjusting a coil compensated become. 29. The device according to claim 1 and 2, characterized in that the manufacturing tolerances of the coil pair (2, 3) are compensated for by adjusting the coil (8/1). 30. The device according to claim 1 and 2, characterized in that two pairs of coils ( 2 , 3 ) and the control logic are protected by a metal housing ( 10 ).