Electronic two-wire switching device

Abstract

Electronic two-wire switching device, comprising: a sensor unit (1), a first two-wire switching output (2) with two terminals (3, 4), a second two-wire switching output (7) with two terminals (5, 6), a voltage regulator (8) to supply the sensor unit (1), a first controller (9) and a second controller (10), both of which are connected to the sensor unit (1), wherein the voltage regulator (8) and the sensor unit (1) are supplied with power exclusively by the first regulator (9), wherein the first regulator (9) is designed as a shunt regulator or Zener diode, so that a residual voltage remains between the terminals (3, 4) even in the conducting state, where the first and second two-wire switching output (2, 7) can switch both equivalently and antivalently and can have different switching points, characterized in that the sensor unit (1) contains magnetoresistive resistors, which are designed as anisotropic (AMR) or gigantomagnetic (GMR) resistors and are arranged in a bridge circuit.

Description

[0001] The invention relates to an electronic two-wire switching device according to claim 1.

[0002] Electronic two-wire switching devices have been known for a long time and are primarily used in automation technology. They are also manufactured and distributed by the applicant.

[0003] From DE 37 14 938 A1 a two-point switch for providing switching signals is known.

[0004] In the course of the development of automation technology, they arose from the need to replace manually operated switches or mechanical limit switches with sensor-controlled electronic switches. Initially, they were primarily designed as inductive proximity switches. Now, versions are available with almost all known sensor types, especially magnetic or capacitive sensors.

[0005] A device for acquiring process variables is known from DE 10 2006 052 291 A1 and DE 10 2007 047 309 A1. A circuit arrangement for speed sensors in a motor vehicle braking system is known from DE 100 62 839 A1. This circuit arrangement acquires and transmits sensor signals. It regulates the signal current to a setpoint in order to process additional signals from another sensor and supply it with current.

[0006] Since there are only two connecting wires, the power supply to the sensor must be ensured in both switching states.

[0007] Therefore, they necessarily exhibit a certain residual current when open and a residual voltage when closed.

[0008] So far, a large number of electronic circuits have been developed for both 220 volts AC and DC voltages from 12 to 36 or 48 volts.

[0009] As can easily be seen, at high voltages the residual current and at low supply voltages the residual voltage is the critical quantity.

[0010] Overall, the goal is of course to keep both the residual voltage and the residual current as low as possible.

[0011] Furthermore, there was a desire to easily adjust or program the switching behavior, i.e., whether the switch opens or closes when an object approaches or when a certain position or setpoint is reached.

[0012] The patent application DE 40 23 502 A1 discloses an inductive proximity switch with terminal programming. This switch has two parallel-connected, antivalent switching outputs. Depending on the polarity of the connecting leads, one or the other is activated. The residual current of these devices is in the range of 5 mA. DE199 47 698 A1 discloses a connection circuit for a measuring device with two terminals, each forming a two-wire interface.

[0013] These two-wire interfaces differ from the aforementioned state of the art in that an analog signal in the range of 4 to 20 mA is transmitted.

[0014] To accommodate the increased power consumption of the sensor, but also to comply with explosion protection guidelines, the power supply is split between both wire pairs, so that more current is available overall, in this case at least 8 mA.

[0015] The disadvantage of the aforementioned state of the art is that a relatively high residual current flows through the connecting lines.

[0016] The aim of the invention is to provide an electronic two-wire switching device that has a significantly lower residual current and a negligible residual voltage in order to save operating current, avoid unnecessary heat generation and better meet safety requirements.

[0017] One object of the invention is to provide an improved electronic two-wire switching device that increases efficiency and safety in operation.

[0018] This task is solved according to the characterizing feature of the main claim.

[0019] The essential inventive idea is to supply the sensor from only one two-wire connection and to control at least one further two-wire connection in parallel.

[0020] The advantage is that at least one switching output with near-ideal characteristics is available. The residual current is only 20-30 µA. The residual voltage can be reduced to as low as 0.1 volts if required. This saves operating current, avoids unnecessary heat generation, and better meets safety requirements.

[0021] The invention is explained in more detail with reference to the drawing. Fig. Figure 1 shows the state of the art Fig. Figure 2 shows an electronic two-wire switching device according to the invention. Fig. Figure 3 shows an embodiment of the invention.

[0022] The Fig. Figure 1 shows a two-wire switching device according to DE 199 47 698 A1. The electrical power-consuming measuring device 1 (sensor unit) is supplied by the voltage regulator 8. The voltage regulator 8 is connected in parallel to the first two-wire interface 2 and the second two-wire interface 7. This allows it to draw energy from both two-wire interfaces 2 and 7.

[0023] The longitudinal controllers 9 and 10 are both controlled by the same measuring device 1, i.e. they also output the same signal.

[0024] The two rectifiers 12 and 13 enable the transmission of alternating current. They can also serve as reverse polarity protection or prevent the backflow of electrical energy from the measuring device 1 to the two-wire interfaces 2 and 7. They are preferably designed as bridge rectifiers.

[0025] The Fig. Figure 2 shows a setup according to the invention. The sensor unit 1 preferably contains a magnetic field sensor. This can, for example, be an anisotropic magnetoresistance (AMR). It is preferably operated in a bridge circuit and evaluated with an instrumentation amplifier. The sensor unit 1 is powered by the voltage regulator 8. It can generate a binary switching signal and preferably includes a microcontroller (µC). According to the invention, the voltage regulator 8, and thus also the sensor unit 1, are supplied with current exclusively by the regulator 9.

[0026] To reduce power consumption, sensor unit 1, or at least parts of it, can be supplied with energy only intermittently (pulsed operation). Controller 9 thus consumes less than 500 µA. Controller 10 is not loaded by sensor unit 1, therefore requires only 20-30 µA, and is thus a nearly ideal switching output.

[0027] The two controllers 9 and 10 can share a common line (supply voltage or ground) or be galvanically isolated. It should be noted that the two controllers 9 and 10 can switch both equivalently and antivalently. Different switching points are also possible. Line programming, for example via the two-wire interface 2, is also possible.

[0028] The two rectifiers 12 and 13 are not strictly necessary for the realization of the invention. They are preferably designed as bridge rectifiers. Their function has already been described above.

[0029] The Fig. Figure 3 shows a further embodiment of the invention. It is intended in particular for monitoring the wear condition of brake pads in wind turbines.

[0030] Sensor unit 1 contains two measuring bridges with magnetoresistive resistors and two instrumentation amplifiers. Their signals are fed to the microcontroller (µC) belonging to sensor unit 1. The microcontroller generates two switching signals that can be used to trigger controllers 9 and 10 depending on the measured values, but independently of each other.

[0031] The voltage regulator 8, and thus also the sensor unit 1, is powered exclusively via the regulator 9, which operates as a shunt regulator. In the open state, the operating voltage of typically 24 or 48 volts is present across the regulator 9. The voltage regulator 8 provides a voltage Ua of, for example, 5 volts.

[0032] In the closed switching state, a residual voltage remains across regulator 9 to supply the sensor unit 1. This does not necessarily have to be higher than the supply voltage of the microcontroller, but can also be regulated upwards. The second regulator 10 is controlled by the microcontroller µC, but does not contribute to its power supply. The resistors R L1 and R L2 These are load resistors connected to terminals 3, 4 and 5, 6, which must be within a specific range of values.

[0033] The electronic two-wire switching device according to the invention comprises a sensor unit 1, a first two-wire switching output 2 with terminals 3 and 4, a second two-wire switching output 7 with terminals 5 and 6, a voltage regulator 8 for supplying the sensor unit 1, which may include a microcontroller for evaluating the sensor signals, and a first regulator 9 and a second regulator 10, both of which are connected to the sensor unit 1. According to the invention, the voltage regulator 8, and thus also the sensor unit 1, are supplied with power exclusively from the first regulator 9.

[0034] The regulator 9 is a shunt regulator or designed as a Zener diode, i.e., even in the conducting state, a residual voltage remains between the terminals (3, 4).

[0035] The second controller 10 can also be designed as a shunt controller, for example to supply power to an indicator LED.

[0036] The two two-wire switching outputs 2 and 7 can also share a common power supply connection. In this case, connections 3 and 5 or 4 and 6 are combined.

[0037] Although the two-wire switching outputs 2 and 7 are both controlled by sensor unit 1, they do not necessarily have to switch in the same way. In some applications, it can be advantageous to program the microcontroller in sensor unit 1 to switch in opposite directions. Of course, different switching points can also be set or learned.

[0038] Magnetoresistive resistors are particularly advantageous as energy-saving sensors. They are available as anisotropic (AMR) or gigantic magnetic (GMR) resistors. They are advantageously arranged in a bridge circuit and evaluated with an instrumentation amplifier. The resulting voltage signal can either be digitized or compared to a threshold value. A binary switching signal can be generated with a trigger circuit or by the microcontroller. When using a microcontroller, additional two-wire switching outputs of type 7 can easily be controlled.

[0039] Provided the required switching frequency allows it, the sensor can be temporarily switched off via the instrumentation amplifier and then re-energized after a pause. This saves energy and reduces the residual current of the controller 9. List of abbreviations: 1 measuring device, sensor unit 2 First two-wire interface, or first two-wire switching output 3. First connection of the first interface 4 Second connection of the first interface 5. First connection of the second interface 6 Second connection of the second interface 7 Second two-wire interface, or second two-wire switching output 8 voltage regulators 9. Linear control transistor, or shunt regulator 10. Linear control transistor, or shunt regulator 11 is omitted 12 rectifiers, preferably in bridge configuration 13 rectifiers, preferably in bridge configuration

Claims

[1] Two-wire electronic switching device, comprising: a sensor unit (1), a first two-wire switching output (2) with two terminals (3, 4), a second two-wire switching output (7) with two terminals (5, 6), a voltage regulator (8) for supplying the sensor unit (1), a first controller (9) and a second controller (10), both connected to the sensor unit (1), wherein the voltage regulator (8) and the sensor unit (1) are supplied with power exclusively by the first regulator (9), wherein the first regulator (9) is designed as a shunt regulator or Zener diode, so that even in the conductive state a residual voltage remains between the terminals (3, 4), wherein the first and second two-wire switching outputs (2, 7) can switch both equivalently and antivalently and can have different switching points, characterized bythat the sensor unit (1) contains magnetoresistive resistors, which are designed as anisotropic (AMR) or gigantomagnetic (GMR) resistors and are arranged in a bridge circuit. [2] Electronic two-wire switching device according to claim 1, characterized by that the magnetoresistive resistors are evaluated with an instrumentation amplifier. [3] Electronic two-wire switching device according to one of the preceding claims, characterized by that the sensor unit (1) has a microcontroller for evaluating the sensor signals. [4] Electronic two-wire switching device according to claim 3, characterized by that the microcontroller in the sensor unit (1) is programmed so that the two-wire switching outputs (2, 7) switch antivalently. [5] Electronic two-wire switching device according to one of the preceding claims, characterized bythat the sensor unit (1) is temporarily supplied with energy in a cyclic operation in order to reduce the power consumed.

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