ELECTRICAL CIRCUIT, IN PARTICULAR FOR AN INDUCTIVELY OPERATED PROXIMITY SWITCH

Description

[0001] The invention relates to an electrical circuit forming an inductively operated proximity switch, according to the preamble of claim 1.

[0002] Such a proximity switch is already known from US 2009 / 0021248 A1. This concerns a proximity switch with improved resistance to environmental influences such as temperature and humidity. During distance measurement, the frequency of a transmitting coil is recorded in an open and closed circuit. The results are compared, with the result being used to determine a switching point.

[0003] Such proximity switches have been known for a long time and feature various circuit designs and associated different modes of operation. For example, DE 103 45 819 B4 describes a proximity switch with an LC resonant circuit and an oscillator circuit for exciting the oscillation in the resonant circuit. An evaluation unit connected downstream of the oscillator circuit monitors the oscillation behavior, particularly the oscillation amplitude of the resonant circuit. When a metallic object approaches the three-dimensional monitoring area, energy is removed from the resonant circuit and the amplitude decreases, so that the proximity switch or the evaluation unit generates a corresponding switching signal.

[0004] In addition, a so-called changeover switch is provided between the oscillating circuit and the evaluation unit, which is switched to a closed and an open position to ensure redundant evaluation.

[0005] However, it has been found to be disadvantageous with such a functional principle of a proximity switch that the evaluation method does not reliably guarantee that a fault in the oscillating circuit is detected if, for example, one or the other electrical component is defective or its associated function is no longer present.

[0006] Another disadvantage is that such a proximity switch has a different switching distance for different metals of the objects entering the monitoring area. For example, for objects made of aluminum or non-ferrous metals such as copper, the switching distance is one-third of that of a steel object. Consequently, the range of applications for such proximity switches is significantly limited.

[0007] A different method can be found, for example, in DE 10 2014 016 217 A1. There, the switching distance is measured using an LC resonant circuit and an oscillator circuit connected in parallel. However, in the proximity switch described there, the evaluation unit evaluates the frequency changes that generate a frequency change in the resonant circuit when a metallic object approaches within the monitoring area.

[0008] While such proximity switches can be used for different metallic materials, as the switching distance does not change due to the different material properties, such proximity switches have the disadvantage of not being able to reliably detect broken or faulty electrical components that could disrupt their function. However, especially in safety-relevant applications of such proximity switches, it is imperative to permanently or at least periodically check the proximity switch and its components to ensure that the proximity switch functions reliably, i.e., that its electrical components are working properly.

[0009] It is therefore an object of the invention to further develop a proximity switch of the type mentioned at the outset in such a way that it can be used for all types of metallic materials without the switching distance of the proximity switch changing significantly due to the different material properties, and that, on the other hand, the electrical components forming the proximity switch are permanently or at least temporarily reliably monitored or checked to determine whether they are functioning and, consequently, a reliable switching distance measurement can be carried out.

[0010] This object is achieved according to the invention by the features of the characterizing part of patent claim 1.

[0011] Further advantageous developments of the invention emerge from the subclaims.

[0012] The fact that a reference coil is assigned to the oscillating circuit, which is connected in parallel to the transmitting coil and the oscillator, that the oscillator is connected to a logic channel, that at least one switch is provided between the reference coil and ground, which switch is closed or opened by the evaluation unit and / or the logic channel, and that data sets are stored and / or programmed into the logic channel of the reference coil, by means of which the functioning of the oscillating circuit can be checked using predetermined frequencies and / or amplitudes, ensures that the electrical components forming the proximity switch are permanently or at least in a predetermined time cycle checked to ensure that they are functioning reliably. On the other hand, a switching signal can be generated due to the frequency change when a metallic object enters the monitoring area.which is independent of the material properties of the respective object.

[0013] Due to the electrical arrangement of two switches and their respective assignment to the transmitting coil and the reference coil, alternating control of the transmitting coil and the reference coil is possible. The transmitting coil measures the switching distance between it and a metallic object immersed in the monitoring area, thus providing an all-metal proximity switch. By alternately switching the reference coil on and off, the electrical components in the oscillating circuit can be tested for their functionality in a time-saving and reliable manner. The control of the transmitting coil is considered the switching phase for the normal operation of the proximity switch; whereas the control of the reference coil is the testing phase for assessing whether the electrical components installed in the proximity switch are actually functional.Such permanent monitoring is used to ensure that the proximity switch can be operated reliably in a safety-relevant application, because as soon as the connection of the reference coil determines that the components used are malfunctioning or that their interaction is disrupted, the proximity switch switches to the safe switching state.

[0014] Data sets can be stored or programmed into both the evaluation unit and the logic channel, which can be used to check the electrical components used. As soon as the reference coil is connected, the oscillating circuit oscillates in a predefined phase sequence, which can be compared with the stored data sets. In the event of corresponding deviations or exceedances of predefined limit values, the proximity switch automatically switches to the safe switching state, because it is necessary to check the functional integrity of the electrical components used.

[0015] The drawing shows an exemplary embodiment of a proximity switch, which is explained in more detail below. In detail: Figure 1a shows an electrical circuit by which an inductively operated proximity switch is formed with a transmitting coil facing a monitoring area and a reference coil connected in parallel thereto, as well as an oscillator and an LC circuit for exciting the transmitting and reference coils, respectively, and with an evaluation unit and a logic channel that communicate with each other, wherein a switch is provided on the transmitting coil and the reference coil for controlling these components, Figure 1b shows the electrical circuit according to Figure 1a with two switches assigned to the reference coil, Figure 2 shows an enlarged view of the transmitting coil and the reference coil, the reference coil being encapsulated in a housing, and Figure 3 shows a frequency-time diagram for the alternating control of the transmitting coil and the reference coil according to the Figures 1a or 1b.

[0016] In the Figures 1a and 1bAn electrical circuit 1 is shown, forming an inductively operated proximity switch. The proximity switch 1 consists of an oscillating circuit 2 in which a transmitting coil 3, a capacitor 4, and an oscillator 5 are connected. The transmitting coil 3, the capacitor 4, and the oscillator 5 form a so-called LC oscillating circuit, which excites the transmitting coil 3.

[0017] The transmitting coil 3 is directed toward a monitoring area 9 into which a metallic object 10 is immersed. As soon as the metallic object 10 is positioned in the area of ​​the transmitting coil 3, it draws energy from the transmitting coil 3 and thus from the resonant circuit 2, thereby changing the frequency of the resonant circuit 2. An evaluation unit 6 is connected downstream of the transmitting coil 3, by which such a frequency change ΔF is detected and converted into an electrical switching signal.

[0018] In order to be able to test the components forming the electrical circuit 1, in particular the capacitor 4 and the oscillator 5, a switch 7 is provided between the transmitting coil 3 and ground, which switch is opened or closed by the logic channel 12. Furthermore, a reference coil 11 is connected in parallel to the transmitting coil 3 and is connected to ground via a switch 131. The switch 131 can be switched on or off by the logic channel 12.

[0019] For the operation of proximity switch 1 and its continuous functional testing, switch 7 of transmitter coil 3 and switch 13 1 of reference coil 11 are alternately opened or closed. For calibration of proximity switch 1, both switches 7 and 13 1 can be closed.

[0020] According to Figure 1bTwo or more switches 13 1 , 13 2 ... 13 n are connected in series to ensure that the reference coil 11 is unconditionally electrically separated from the circuit 2. If multiple switches 13 1 , 13 2 are present and these switches are open at the same time, the reference coil 11 is decoupled from the circuit 2 if one of the switches 13 1 or 13 2 is open. If one of the switches 13 1 or 13 2 is defective and does not achieve voltage separation, the reference coil 11 is still electrically connected to the circuit 1.

[0021] Data sets relating to the oscillation behavior of the circuit 2 are stored and / or programmed into the evaluation unit 6 and the logic channel 12. If the transmitting coil 11 is electrically decoupled from the circuit 2 by the open switch 7 and the reference coil 11 is connected to the circuit 1 by the closed switch 13 1 or the two closed switches 13 1 and 13 2, then the oscillating circuit 2 will oscillate, but an undetected metallic object 10 will not draw any energy from the reference coil 11 and thus from the oscillating circuit 2. The oscillation behavior of the reference coil 11 is the only way to determine whether and to what extent the electrical components of the oscillating circuit 2 are functional and correctly connected. A comparison of the measured values ​​determined with the actual values ​​stored in the evaluation unit 6 orThe logic channel 12 therefore provides precise information as to whether the proximity switch 1 is functional and can therefore continue to be used reliably in a safety-relevant application.

[0022] In order to ensure that energy is extracted from the resonant circuit 2 exclusively through the transmitting coil 3 when a metallic object 10 approaches the monitoring area 9, the transmitting coil 3 is directed towards the monitoring area 9 and the reference coil 11 is arranged at a significantly greater distance from it. Furthermore, the reference coil 11 is arranged according to Figure 2 encapsulated in a housing 14 so that the reference coil 11 is not influenced in its oscillation behavior by the approaching object 10.

[0023] Furthermore, Figure 2It can be seen that the diameter of the winding of the transmitting coil 3 is substantially larger than the diameter of the reference coil 11. In a preferred embodiment, the diameter of the winding of the transmitting coil 3 is approximately 25 to 30 mm and the diameter of the reference coil 11 is approximately 1 to 3 mm.

[0024] The transmitting coil 3 can also be designed as a conductor coil or planar coil.

[0025] In Figure 3The oscillation behavior of the transmitting coil 3 and the reference coil 11 is shown in a frequency-time diagram. The transmitting coil 3 oscillates sinusoidally at a predetermined frequency, and as soon as the switch 7 is opened and the transmitting coil 3 is consequently electrically decoupled from the resonant circuit 2, it no longer generates oscillation in the resonant circuit 2. At the same time, the switch 13 1 or both switches 13 1 and 13 2 are closed, so that the reference coil 11 determines the oscillation in the resonant circuit 2, and during this time window, a check of the components used in the resonant circuit 2 can be carried out by the evaluation unit 6 or the logic channel 12. The evaluation unit 6 and the logic channel 12 communicate with each other; this is shown schematically.If the existing measured values ​​correspond to the stored actual values ​​and no malfunctions can be detected, the switch 13 1 can be opened and the switch 7 can be closed, so that the proximity switch 1 is converted into its usual inductive operating mode.

Claims

1. Electrical circuit forming an inductively operated proximity switch (1), consisting of: - a resonant circuit (2), in which a transmitting coil (3), a capacitor (4) and an oscillator (5) exciting the transmitting coil (3) are connected in parallel, - a downstream evaluation unit (6), by means of which the amplitude (A) and the frequency (F) of the resonant circuit (2) can be detected, - a monitoring region (9) associated with the transmitting coil (3), in which an object (10) which is present there draws energy from the resonant circuit (2), as a result of which a frequency (ΔF) and / or amplitude change (ΔA) of the resonant circuit (2) can be detected in the evaluation unit (6) and converted into a switching signal, wherein the resonant circuit (2) is associated with a reference coil (11) which is connected in parallel with the transmitting coil (3) and the oscillator (5), in that the resonant circuit (2) has a switch (7) which is arranged between the transmitting coil (3) and a zero potential, and which can be transferred into an open and a closed switching position (SO, SG) by a logical channel (12), in that between the reference coil (11) and the zero potential, at least one switch (131, 132...) is provided which is closed or opened by the logical channel (12), in that the proximity switch is designed to operate in a safety-relevant application, wherein data sets are stored and / or programmable in both the evaluation unit (6) and the logical channel (12) of the reference coil (11), by means of which data sets the functioning of the resonant circuit (2) can be checked on the basis of predetermined frequencies (F) and / or amplitudes (A), by the evaluation unit (6) and the logical channel (12) determining measured values for the vibration behavior of the resonant circuit (2) and comparing these to the actual values stored in the evaluation unit (6) or the logical channel (12), in that the switches (7, 131, 132...) of the transmitting coil (3) and the reference coil (11) are alternately opened or closed, and in that during a checking phase, in which the switch (7) that disconnects the transmitting coil (3) from ground is opened and the at least one switch (131, 132...) that disconnects the reference coil (11) from ground is closed, the evaluation unit (6) and the logical channel (12) exchange data sets in the form of signals and / or data, which are compared to one another in the evaluation unit (6) or the logical channel (12), in such a way that, on the basis of the comparison result, it can be detected that the resonant circuit (2) is functioning correctly and that, in the event of a fault being detected, the proximity switch (1) is switched off.

2. Electrical circuit according to claim 1, characterized in that the switches (7, 131, 132...) are designed as transistors, and in that when the transistors (7, 131, 132...) of the transmitting coil (3) and the reference coil (11) are alternately switched, they are switched to an internal reference inductance, and in that the reference inductance together with the capacitor (4) of the resonant circuit (2) and the oscillator (5) generate a reference measuring frequency which is checked for faults in the evaluation unit (6) and / or the logical channel (12).

3. Electrical circuit according to either of the preceding claims, characterized in that the transmitting coil (3) is arranged immediately adjacent to the monitoring region (9), and in that the reference coil (11) is spaced apart from the monitoring region (9) and / or is encapsulated by an electrically conductive housing (14) in such a way that only the object (10) present in the monitoring region (9) influences the vibration behavior of the resonant circuit (2) by means of the electrical communication between said object and the transmitting coil (3).

4. Electrical circuit according to any of the preceding claims, characterized in that the winding of the transmitting coil (3) has a diameter of 25 to 30 mm, and the winding of the reference coil (11) has a diameter of 1 to 2 mm.

5. Electrical circuit according to any of the preceding claims, characterized in that the transmitting coil (3) is designed as a printed circuit board coil or a planar coil.

6. Electrical circuit according to any of the preceding claims, characterized in that the transmitting coil (3) and the reference coil (11) are assigned a measuring sensor (15), by means of which the temperature in the region of the transmitting coil (3) and the reference coil (11) is detected, and in that the determined temperature values are sent to the evaluation unit (6) and the logic channel (12) for monitoring the prevailing temperature and the associated frequency (ΔF) and / or amplitude change (ΔA).