Proximity switch and method for operating a proximity switch

Abstract

A proximity switch is disclosed. In an embodiment, the proximity switch has a defined detection range and includes an oscillator, an oscillator amplifier, a temperature sensor, a microprocessor and a storage medium. The oscillator generates an alternating magnetic field and changes its oscillation state as a result of a target entering the detection range. The oscillator amplifier is configured to be controllable in an open-loop and closed-loop manner and has at least one amplifier stage. In this embodiment, the at least one amplifier stage has a controllable temperature compensation circuit which is configured to influence the oscillation behaviour of the oscillator based on compensation values received as control data from the microprocessor and/or from the storage medium, depending on a temperature detected by the temperature sensor. The disclosed embodiments also encompass a method for operating a proximity switch with temperature compensation.

Claims

1. A proximity switch having a defined detection range, the proximity switch comprising: an oscillator configured to generate an alternating magnetic field and change its oscillation state as a result of a target entering the detection range; at least one oscillator amplifier; at least one temperature sensor configured to detect a temperature of an element of the proximity switch or an ambient temperature, wherein the oscillator amplifier is configured to be controllable in an open-loop and closed-loop manner and has at least one amplifier stage, and the oscillator is controllable based on the temperature detected by the temperature sensor; at least one microprocessor configured to control a gain of the oscillator amplifier, and at least one storage medium coupled to the microprocessor and configured to store compensation data, wherein the at least one amplifier stage of the oscillation amplifier has a controllable temperature compensation circuit configured to influence an oscillation behavior of the oscillator based on compensation values, as control data, from the microprocessor or from the storage medium, depending on the temperature detected by the temperature sensor.

2. The proximity switch according to claim 1, wherein the temperature compensation circuit is arranged in an emitter branch of the at least one amplifier stage.

3. The proximity switch according to claim 1, wherein the oscillator amplifier has two amplifier stages.

4. The proximity switch according to claim 3, wherein the temperature compensation circuit is incorporated in a first amplifier stage of the two amplifier stages.

5. The proximity switch according to claim 4, wherein one temperature compensation circuit is incorporated in each of the first amplifier stage and a second amplifier stage of the two amplifier stages.

6. The proximity switch according to claim 1, wherein the temperature compensation circuit (comprises a digital potentiometer.

7. The proximity switch according to claim 1, wherein the temperature compensation circuit comprises an operational amplifier configured as a voltage follower and for decoupling the microprocessor from the oscillator amplifier, wherein the operational amplifier is formed to receive a pulse-width modulation (PWM) value as a compensation value, and wherein a control line for the operational amplifier includes a resistor and a capacitor.

8. The proximity switch according to claim 1, wherein the temperature compensation circuit comprises an operational amplifier configured as a voltage follower and for decoupling the microprocessor from the oscillator amplifier, wherein the operational amplifier is formed to receive and process an analog value as a compensation value, and wherein a control line for the operational amplifier includes a digital-to-analog converter.

9. The proximity switch according to claim 1, wherein the temperature sensor is configured to detect a temperature of the oscillator amplifier.

10. The proximity switch according to claim 1, wherein the proximity switch is an inductive proximity switch and the temperature sensor is configured to detect a temperature of a coil of the proximity switch.

11. A method for operating a proximity switch comprising an oscillator and at least one oscillator amplifier, the method comprising: generating, by the oscillator, an alternating magnetic field which changes its oscillation state because of a target entering a detection range for the proximity switch; detecting, by a temperature sensor, a temperature of an element of the proximity switch or an ambient temperature; sending data associated with measured values from the temperature sensor to a microprocessor or to a storage medium coupled to the microprocessor, wherein compensation data is stored on the storage medium; generating, by the microprocessor, control data, wherein the generating is based on the temperature detected by the temperature sensor and the compensation data stored on the storage medium; and sending, by the microprocessor, the control data to at least one temperature compensation circuit of the at least one oscillator amplifier.

12. The method according to claim 11, wherein the oscillator amplifier includes at least one amplifier stage.

13. The method according to claim 11, wherein the temperature sensor detects the temperature of the at least one oscillator amplifier.

14. The method according to claim 12, wherein the temperature sensor detects the temperature of the at least one amplifier stage.

15. The method according to claim 11, wherein the temperature sensor detects the temperature of at least one coil within the proximity switch.

16. The method according to claim 11, wherein sending the control data includes sending the compensation data.

17. The method according to claim 11, wherein the detecting is performed at least intermittently.

18. The method according to claim 12, wherein the oscillator amplifier includes two amplifier stages.

19. The method according to claim 18, wherein the temperature compensation circuit is coupled to a first amplifier stage of the two amplifier stages.

20. The method according to claim 19, wherein one temperature compensation circuit is coupled to each of the first amplifier stage and a second amplifier stage of the two amplifier stages.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further details and advantages of the disclosed embodiments will now be explained in more detail on the basis of example embodiments represented in the drawings. There are shown in:

[0045] FIG. 1 is a circuit diagram illustrating the proximity switch according to an embodiment,

[0046] FIG. 2 illustrates certain elements of the circuit diagram according to FIG. 1 for an alternative embodiment of the proximity switch,

[0047] FIG. 3 is a circuit diagram illustrating a first embodiment of a temperature compensation circuit,

[0048] FIG. 4 is a circuit diagram illustrating a second embodiment of a temperature compensation circuit as an improvement of the design according to FIG. 3,

[0049] FIG. 5 is a circuit diagram illustrating a third embodiment of a temperature compensation circuit, and

[0050] FIG. 6 is a circuit diagram illustrating a fourth embodiment of a temperature compensation circuit.

DETAILED DESCRIPTION

[0051] FIG. 1 shows a circuitry or a circuit diagram for the proximity switch 1 according to the disclosed embodiments. The oscillator 2 or transmission coil 3 is connected via the line 6 to a voltage source via the line 6. In the present case, the transmission coil 3 interacts in a known manner with receiver coils 7. The construction and mode of operation thereof will not be explained further in the present case, in particular not the usual electronic elements for balancing the switching distance.

[0052] The oscillator 2 comprises an oscillation amplifier 10, which comprises a first amplifier stage 11 and a second amplifier stage 12. In addition, the circuitry of the proximity switch 1 has a, schematically represented, microprocessor 15, which is connected to an output driver 20 at least in a data-carrying manner, preferably is connected in a data- and current-carrying manner via a current-modulated line.

[0053] A temperature compensation circuit 13, which is described in more detail in FIGS. 2 to 6 below, is provided in the emitter branch 17 of the first amplifier stage 11. The emitter branch 18 of the second amplifier stage 12 is formed without a temperature compensation circuit. The other (micro-)electronic components can be identified by their respective symbols and are not described in more detail.

[0054] In the lower region of FIG. 1, a temperature sensor 5 is also represented, which is connected to the microprocessor 15 via the line 8 and is also independently connected to a voltage source. In the microprocessor 15, the measured values received from the temperature sensor 5 are detected, evaluated and compared with the compensation values, temperature algorithms and/or temperature-dependency data stored in the storage medium 16. The microprocessor 15 then sends control data to the temperature compensation circuit 13 via the control line 9.

[0055] In the embodiment according to FIG. 2, the circuit according to FIG. 1 is represented in simplified form, and identical reference numbers have the same meaning and therefore in some cases are not named and/or explained again. In the example shown, the oscillation amplifier 10 has the temperature compensation circuit 13 in the first amplifier stage 11. In addition, a temperature compensation circuit 14 is also arranged in the second amplifier stage 12 in the emitter branch of the second amplifier stage 12.

[0056] In the present case, these temperature compensation circuits 13, 14 are structurally identical and formed in accordance with an embodiment according to FIGS. 3 to 6. The two temperature compensation circuits 13, 14 receive the control data for compensating for the temperature influences from the microprocessor 15 or from the storage medium 16. The control data are supplied to the two temperature compensation circuits 13, 14 via the control lines 9.

[0057] In each case in the embodiment example according to FIG. 3 and in the further FIGS. 4 to 6, only the first amplifier stage 11 and the temperature compensation circuit 13 arranged in the emitter branch 17 is, wherein comparable or identical elements and/or circuits of the temperature compensation circuit can also be provided in each case in the second amplifier stage 12 and/or in the two emitter branches 17, 18. Compared with FIGS. 1 and 2, the circuit is represented in an even more simplified form. The first embodiment of the temperature compensation circuit 13, shown in FIG. 3, is formed as a digital potentiometer 21. For example, a resistor that can be controlled in a stepless manner (rheostat) and/or another switchable micro-electronic component form(s) the core piece in this case.

[0058] In the second embodiment of the temperature compensation circuit 13 according to FIG. 4, a digital potentiometer 21 is provided, analogously to FIG. 3, wherein an earthed line branch 19, in parallel therewith, with a resistor 29 is additionally arranged for adjusting the sensitivity of the digital potentiometer 21.

[0059] FIG. 5 shows a third embodiment of the temperature compensation circuit 13, in which an operational amplifier 22 is comprised as a voltage follower and for decoupling the microprocessor 15 from the oscillator amplifier 10. In this case, the operational amplifier 22 is formed to receive a pulse-width modulation (PWM value) as the control data and/or compensation values via the control line 9, the RC path.

[0060] For the purpose of attenuation and signal smoothing, a resistor 26 can be arranged in the control line 9, as also shown in the example according to FIG. 5, and a line branch-off 24 in which a capacitor 25 is arranged can be arranged between the resistor 9 and the operational amplifier 22. Together with the resistor 26, the capacitor 25 forms a low-pass filter which converts the PWM signal into an equivalent DC voltage.

[0061] The PWM resolution represents a measure for the sensitivity of the control and is at a 12-bit resolution in the example shown.

[0062] Lastly, FIG. 6 shows the fourth embodiment of the temperature compensation circuit 13, in which, analogously to the embodiment according to FIG. 5, an operational amplifier 27 is provided as a voltage follower and for decoupling the microprocessor 15 from the oscillator amplifier 10. The latter is formed to receive and process analogue values as control data or compensation values. In the example shown, digital control data are sent to the operational amplifier 27 via the control line 9, the RC path, by the microprocessor 15, with the result that a digital-to-analogue converter 23 is arranged in the control line 9. The digital-to-analogue converter 23 can also be arranged upstream of the microprocessor 15 or interact with the storage medium independently and prepare the storage data in a suitable way for the microprocessor 15 and/or the operational amplifier 27.

[0063] In this embodiment variant, the quantization of the digital-to-analogue converter determines the sensitiveness of the temperature control, wherein a 12-bit resolution has also been effected in this example. The advantage of using digital-to-analogue converters is that they are already contained in many microprocessors. Furthermore, compared with the variant shown in FIG. 5, no low-pass filter is required, which reduces component costs.

[0064] It is immediately apparent to a person skilled in the art that the above embodiments have been described independently as subject matters but can be combined in parts according to requirements.

LIST OF REFERENCE NUMBERS

[0065] 1 Proximity switch

[0066] 2 Oscillator

[0067] 3 Transmission coil

[0068] 5 Temperature sensor

[0069] 6 Line

[0070] 7 Receiver coils

[0071] 8 Line

[0072] 9 Control line, RC path

[0073] 10 Oscillator amplifier

[0074] 11 Amplifier stage

[0075] 12 Amplifier stage

[0076] 13 Temperature compensation circuit

[0077] 14 Temperature compensation circuit

[0078] 15 Microprocessor

[0079] 16 Storage medium

[0080] 17 Emitter branch

[0081] 18 Emitter branch

[0082] 19 Line branch

[0083] 20 Output driver

[0084] 21 Digital potentiometer

[0085] 22 Operational amplifier

[0086] 23 Digital-to-analogue converter (DAC)

[0087] 24 Line branch

[0088] 25 Capacitor

[0089] 26 Resistor

[0090] 27 Operational amplifier

[0091] 29 Resistor

[0092] 30 Detection range