Device and method for detecting and monitoring an analogue measured variable

Abstract

The invention relates to a device (1) for detecting and monitoring an analogue measured variable, wherein the device (1) has at least one sensor (2) for detecting the analogue measured variable, an analogue input filter (5), a delta-sigma modulator (6), a downstream filter (7) and a comparison unit (8), wherein the delta-sigma modulator (6) is designed to supply a bit stream (BS) to the downstream filter (7), wherein the delta-sigma modulator (6) and filter (7) are clocked synchronously, wherein a switching device (11) is arranged between the delta-sigma modulator (6) and the filter (7), wherein the switching device (11) has an input for at least one control signal (SS) of an interference source (13) for the measured variable, wherein the switching device (11) is designedwithout a control signal (SS), to switch the bit stream (BS) of the delta-sigma modulator (6) through to the filter (7) and, in the presence of a control signal (SS), to switch through a substitute bit stream (EBS) which is judged to be permissible by the comparison unit (8), and an associated method.

Description

The invention relates to a device and a method for detecting an analog measured variable.DE 10 2021 131 791 A1 discloses a method for operating an electrical circuit arrangement comprising at least a first component and a second component, wherein the components are electrically connected via a direct current subnetwork of the electrical circuit arrangement, wherein the first component switches at a first operating point with a first timing and the second component switches at a second operating point with a second timing, wherein the components are connected via a communication connection and a first phase position is determined as a function of at least one item of fault information describing a current alternating voltage in the direct current subnetwork and is set between the first timing and the second timing.DE 10 2022 101 903 A1 relates to a method and a device for monitoring a measurement chain with a sensor. The problem of monitoring the sensor evaluation in a circuit for regulating electrical drives is dealt with. To ensure that a measurement circuit is functioning correctly, a noise-shaped test signal is fed into the signal processing and the result at the output is verified.Components clocked in this way are frequently sources of interference for measured variables. If, for example, the voltage is to be measured and monitored in such a direct current subsystem, these superimposed alternating voltages lead to problems, in particular if it is to be switched off very quickly in the case of overvoltage. Typical reaction times in high-voltage traction networks are on the order of magnitude of 10 μs.It is known here to use delta-sigma modulators for measuring analog measured variables or, in particular, for digitizing them, which convert an analog measured value into a bit stream, which is then sent to a filter, at whose output a digital measurement signal is then present. The filter is preferably a digital low-pass filter. In principle, for the bit stream, the more positive the input signal is, the more positive bits are included, and the more negative the input signal is, the more negative bits are included. A special case represents an input value of zero. In this case, as many negative as positive bits are included, and the modulator outputs negative and positive bits alternately. This can also be referred to as a zero bit stream. As already stated, such measuring arrangements with delta-sigma modulators are very fast compared to conventional digital signal processing in a microcontroller, but here too the problems arise due to short interference pulses due to clocked interference sources, which frequently lead to unnecessary shutdown.The invention is based on the technical problem of creating a device for detecting and monitoring an analog measured variable which is fast and robust with respect to disturbing influences. A further technical problem is to provide a corresponding method.The solution of the technical problem is achieved by a device having the features of claim 1 and a method having the features of claim 8.The device for detecting and monitoring an analog measured variable has at least one sensor for detecting the analog measured variable, an analog input filter, a delta-sigma modulator, a downstream filter and a comparison unit. The delta-sigma modulator is designed to supply a bit stream to the downstream filter, the delta-sigma modulator and the downstream filter being clocked synchronously. Furthermore, a changeover device is arranged between the delta-sigma modulator and the filter, wherein the changeover device has at least one input for at least one control signal of an interference source for the measurement variable. The switching device is designed in such a way that the bit stream of the delta-sigma modulator is switched through to the filter without control signal from the interference source and a substitute bit stream is switched through in the presence of a control signal, which is judged as permitted by the comparison unit. The basic idea here is to switch off the real measurement signal during the disturbance and to replace it with a pseudo signal (substitute bit stream) which complies with the criteria of the comparison device, so that the temporary disturbances do not lead to a false triggering. The switching device acts as a multiplexer. In this case, the substitute bit stream is switched through for the time of a switching edge and a certain settling time. The time period is about 1 μs, so that sufficient time still remains (e.g. 9 μs) to monitor the undisturbed measurement signal.In one embodiment, the replacement bitstream is a zero bitstream, preferably generated by a divider of the clock signal. If the clock signal is, for example, a 20 MHz clock, a 10 MHz or 5 MHz clock signal is generated, for example, which alternately has positive or negative bits, as is to be the case with a zero bit stream.In an alternative embodiment, a holding element is provided which temporarily stores output signals of the filter, wherein the device has a further delta-sigma modulator which is connected on the input side to the holding element and is connected on the output side to the switching device, wherein the further delta-sigma modulator supplies the substitute bit stream. The idea here is to feed back measured values as a substitute bit stream shortly before the disturbance, so that these values are closer to the real measured values, which has advantages during the evaluation, since this form of the substitute bit stream distorts the measured values less than a zero bit stream.In a further embodiment, the sensor is a voltage sensor which further preferably measures a high-voltage voltage in a traction network of an electric vehicle.In a further embodiment, the control signals are switching edges of a pulse inverter or of a DC / DC converter.In a further embodiment, the further delta-sigma modulator is designed as an FPGA or is implemented in a microcontroller, since the requirements imposed on the further delta-sigma modulator are lower.With regard to the embodiment according to the method, reference can be made in full to the preceding explanations.The invention is explained in more detail below with reference to preferred exemplary embodiments. The figures show: FIG. 1 shows a schematic illustration of a device for detecting and monitoring an analog measured variable in a first embodiment, and FIG. 2 shows a schematic illustration of a device in a second embodiment.FIG. 1 shows a device 1 for detecting and monitoring an analog measured variable. The device 1 has a sensor 2 for detecting the analog measured variable. In the example shown, the sensor 2 is a voltage sensor 3 connected to DC terminals 4 of a traction network of an electric vehicle. Furthermore, the device 1 has an analog input filter (anti-aliasing filter) 5, which supplies the filtered measured variables to a delta-sigma modulator 6 as input variable. The cut-off frequency of the input filter 5 acting as a low-pass filter is selected in such a way that the sampling of the delta-sigma modulator 6 complies with the sampling theory. Delta-sigma modulator 6 functions as an AD converter. Delta-sigma modulator 6 is designed as hardware. Delta-sigma modulator 6 generates a clock signal TS for a digital filter 7. digital filter 7 converts the digital bit stream into a multi-bit digital value. A comparison unit 8 is arranged at the output of the digital filter 7, which compares the output signals of the digital filter 7 with at least one threshold value, wherein, if the threshold value is exceeded, a switch-off device 9 is controlled, which is designed as a relay, for example. Furthermore, a storage device 10 is shown in which the digital measured values of the digital filter 7 are stored. Furthermore, the apparatus 1 has a changeover device 11 which receives the bit stream BS from the delta-sigma modulator 6 on the input side. Furthermore, the apparatus 1 has a divider 12 for the clock signal TS, which divides the clock signal TS by two or four, for example. The generated signal is a substitute bit stream EBS in the form of a zero bit stream NBS, i.e. the signal stands for a measurement value zero which has as many positive bits as negative bits. The substitute bit stream EBS is likewise fed on the input side to the switching device 11. The switching device 11 is supplied with a control signal SS of an interference source 13. The interference source 13 is, for example, a pulse inverter or a DC / DC converter, wherein the control signals SS are the switching edges of the power transistors of the interference source 13. If no control signals SS are present, the switching device 11 switches through the bit stream BS from the delta-sigma modulator 6 to the digital filter 7. If, on the other hand, the disturbance source 13 generates a switching signal SS, the switching device 11 switches over to the substitute bit stream EBS, which in this embodiment is a zero bit stream NBS. This changeover remains for the duration of the switching signal plus a certain settling time, with the changeover then subsequently being made again to the bit stream BS of the delta-sigma modulator 6. The substitute bit stream EBS is therefore only briefly switched through at the time of the fault, so that it is prevented that the comparison unit 9 incorrectly detects an overvoltage which would lead to an unnecessary switching off.FIG. 2 shows an alternative embodiment of a device 1, wherein identical elements are provided with identical reference numerals. In contrast to the embodiment according to FIG. 1, the device 1 has a holding element 14 and a further delta-sigma modulator 15. The latch 14 latches the output signals of the digital filter 7. The holding element 14 is connected on the input side to the further delta-sigma modulator 15, the further delta-sigma modulator 15 generating the substitute bit stream. The further delta-sigma modulator 15 is clocked with the clock signal TS synchronously with the digital filter 7. If the disturbance source 13 then generates a switching signal SS, the data from the holding element 14 are fed to the further delta-sigma modulator 15, which generates a substitute bit stream EBS therefrom, which is switched through by the switching device 11 to the digital filter 7 and is further processed. As a result, the digital filter 7 receives a substitute bit stream EBS corresponding to the bit stream BS before the switching signals SS occur. As a result, the measured values at the output of the digital filter are more realistic than the measured values due to the zero bit current NBS according to FIG. 1, wherein the component outlay is somewhat greater, however.List of reference characters1 Device 2 Sensor 3 Voltage sensor 4 DC terminal 5 Analog input filter 6 Delta-sigma modulator 7 Digital filter 8 Comparison unit 9 Switch-off device 10 Storage device 11 Switching device 12 Divider 13 Disturbance source 14 Holding element 15 Delta-sigma modulator BS Bit stream EBS Replacement bit stream NBS Zero bit stream TS Clock signal SS Switching signal

Claims

Device (1) for detecting and monitoring an analog measurement variable, wherein the device (1) has at least one sensor (2) for detecting the analog measurement variable, an analog input filter (5), a delta-sigma modulator (6), a downstream filter (7) and a comparison unit (8), wherein the delta-sigma modulator (6) is designed to feed a bit stream (BS) to the downstream filter (7), wherein the delta-sigma modulator (6) and filter (7) are clocked synchronously, characterized in that a switching device (11) is arranged between the delta-sigma modulator (6) and the filter (7), wherein the switching device (11) has an input for at least one control signal (SS) of an interference source (13) for the measurement variable, wherein the switching device (11) is designed such that, The result is that the bit stream (BS) of the delta-sigma modulator (6) is switched through to the filter (7) without a control signal (SS) and a substitute bit stream (EBS) is switched through in the presence of a control signal (SS), which is judged as being permissible by the comparison unit (8).Device according to Claim 1, characterized in that the replacement bit stream (EBS) is a zero bit stream (NBS).Device according to Claim 2, characterized in that the replacement bit stream (EBS) is generated by a divider (12) of the clock signal (TS).Device according to Claim 1, characterized in that a holding element (14) is provided which stores the output signal of the filter (7), wherein the device (1) has a further delta-sigma modulator (15) which is connected on the input side to the holding element (14) and is connected on the output side to the switching device (11), wherein the further delta-sigma modulator (15) delivers the substitute bit stream (EBS).Device according to one of the preceding claims, characterized in that the sensor (2) is a tension sensor (3).Device according to one of the preceding claims, characterized in that the control signals (SS) are switching edges of a pulse inverter.Device according to Claim 4, characterized in that the further delta-sigma modulator (15) is designed as an FPGA or is implemented in a microcontroller.Method for detecting and monitoring an analog measurement variable, wherein the analog measurement variable is detected by means of at least one sensor (2) and filtered by means of an analog input filter (5), wherein the filtered values are digitized into a bit stream (BS) by means of a delta-sigma modulator (6) and are converted into a multi-bit value by means of a filter (7), wherein the digitized output values of the filter (7) are compared with at least one threshold value in a comparison unit (8), wherein the delta-sigma modulator (6) and the filter (7) are clocked synchronously, characterized in that a switching device (11) is arranged between the delta-sigma modulator (6) and the filter (7), said switching device having at least one input for at least one control signal (SS) of an interference source (13) for the measurement variable, wherein the switching device (11) switches through the bit stream (BS) of the delta-sigma modulator (6) to the filter (7) without a control signal (SS) and, in the presence of a control signal (SS), switches through a substitute bit stream (EBS) to the filter (7) which is judged as being permissible by the comparison unit (8).Method according to Claim 8, characterized in that the replacement bit stream (EBS) is a zero bit stream (NBS).Method according to Claim 8, characterized in that output signals of the filter (7) are buffer-stored by means of a holding element (14), said output signals then being fed to a further delta-sigma modulator (15), the further delta-sigma modulator (15) being connected to the switching device (11) and supplying the substitute bit stream (EBS).

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