Method for detecting the deterioration of data transmission quality between a transmitter and a sensor

Abstract

The invention discloses a method for detecting the deterioration of the quality of the data transmission between a transmitter and a sensor, in particular via a cable, via a control loop, wherein the data transmission is actively disturbed by the disturbance variable and the disturbance variable is tracked in the control loop in such a way that a constant error rate results in the data transmission, wherein the error rate is greater than 0, wherein the disturbance variable is correlated to the signal-to-noise ratio of the data transmission, and thus to the quality of the data transmission. The invention further discloses a system.

Description

[0001] The invention relates to a method for detecting deterioration in the quality of data transmission between a transmitter and a sensor, particularly via a cable. The invention also relates to a corresponding system.

[0002] A transmitter – also called a measuring transducer – is generally a device that converts an input variable into an output variable according to a fixed relationship. In process automation technology, a field device is connected to a measuring transducer. The field device is, for example, a sensor. Its raw measured values ​​are processed in the measuring transducer, for example, averaged or converted into another variable using a calibration model, such as the process variable to be determined, and possibly forwarded, for example, to a control system. The transmitter is connected to the sensor via a cable. Alternatively, a wireless connection exists between the transmitter and sensor.

[0003] During communication between the transmitter and the sensor(s), interference can occur via the cable connections used, which can negatively affect the data transmission.

[0004] Such interference can be caused by damage and aging effects, such as damage to the cable insulation or between the signal conductors. Penetrating moisture can then introduce external electrical interference into the signal lines, short-circuit them, or at least dampen them, thus disrupting transmission. Above all, electromagnetic influences also affect signal transmission quality. Strong electromagnetic fields, such as those caused by frequency converters for electric motors, welding and switching processes involving heavy loads, and even radio transmissions, negatively impact data transmission and can disrupt it, even if the cable is physically undamaged.

[0005] Using checksums or bit error correction coding, errors in signal transmission can be detected and, if necessary, corrected. However, these measures only take effect once the digital transmission has already been disrupted, and they are unable or only poorly able to track a "creeping trend" and thus indicate problems early on. While an accumulation of communication disruptions can be detected, the transmission itself is already negatively impacted.

[0006] The invention is based on the object of detecting negative influences on the data transmission between a transmitter and a sensor at an early stage, ideally before the transmission itself is impaired.

[0007] The task is solved by a method using a control loop, whereby the data transmission is actively disturbed by the disturbance variable and the disturbance variable is tracked in the control loop in such a way that a constant error rate is achieved during data transmission, whereby the error rate is greater than 0, whereby the disturbance variable is correlated to the signal-to-noise ratio of the data transmission and thus to the quality of the data transmission.

[0008] The problem is thus solved by detecting negative external influences on the data transmission lines at an early stage, and by providing the disturbance variable as a qualitative parameter before the transmission itself is affected. This quality parameter represents a measure of the currently achieved interference immunity of a data transmission connection.

[0009] If the value of this parameter decreases slowly over time, it indicates a progressive deterioration (e.g., insulation faults). If it decreases very suddenly, the time point can be used as an indicator to attribute the negative external influence to activities in the system installation (maintenance and modification work). For example, this could be caused by the installation of a poorly suppressed electric motor or by welding processes in the system.

[0010] In one embodiment, the disturbance is proportional to the signal-to-noise ratio of the data transmission. Proportionality is a special case of correlation in which the rate of change is constant. In one embodiment, the disturbance and the signal-to-noise ratio of the data transmission are nonlinearly related, with the rate of change varying.

[0011] The claimed solution to the problem thus involves the active (artificial) degradation of the signal transmission path based on a control loop. The interference quantity is always tracked in such a way that a constant data transmission error rate results. The magnitude of this interference quantity then correlates with the signal-to-noise margin of the data transmission. The interference quantity is changed in such a way that just enough of a signal still arrives, or that the signal-to-noise margin is above a threshold value.

[0012] The property can be exploited that common data transmission protocols implement repetitions in case of data transmission errors, so that this regulation is possible without changing the data transmission protocol and only the frequency of packet repetitions of the used data transmission protocol is passively monitored by the control algorithm.

[0013] The control algorithm only tracks the disturbance to a very minimal extent to avoid (excessively) negatively impacting the data transmission itself. One possible measure could be, for example, to perform this measurement (and thus active disturbance) only relatively rarely or during non-critical phases of system operation. It is also conceivable for a user to initiate an explicit "measurement" of the communication link.

[0014] In one embodiment, the data transmission protocol is supplemented by a test data packet, which is sent back and forth between the transmitter and sensor solely to determine the current transmission quality. The active interference is then generated only for the duration of this test data packet, so that normal communication operation itself is not impaired. This test data packet can be inserted during the communication pauses that usually occur anyway, so that there is no change in the primary payload data transmission. In particular, in this variant, normal data transmission is never disrupted, so that the quality of the data transmission itself is not impaired despite continuously running transmission quality measurements.

[0015] The test data packet can be equipped with forward error-correcting codes, allowing the sensor to read the data packet already received with errors, determine the number of bit errors, and transmit the received bit errors back to the transmitter in the response packet using this type of coding. This allows the bit error rate to be determined in both directions, even under higher levels of interference.

[0016] As an embodiment, a test data packet can be announced by the transmitter (initially without activated interference); immediately afterwards, the test data packet is transmitted (from transmitter to sensor), the sensor determines the bit error rate and stores it. The artificial interference is then terminated. In the undisturbed phase, the transmitter can request the determined bit error rate from the sensor. In a second cycle, the transmitter (still undisturbed) requests a test data packet from the sensor, activates the interference, receives the test data packet, calculates the bit error rate, and stores it. The artificial interference is then terminated so as not to impair regular data transmission.

[0017] Artificial disruption of data transmission can occur in a variety of ways: • Capacitive coupling of an interference signal (amplitude, frequency, and signal shape can be adjusted) to the communication signals. Alternatively, an unused cable conductor can be used for signal coupling; the coupling then occurs purely capacitively via the adjacent conductor wires of the cable. • Electronically adjustable attenuators (e.g. galvanically isolated PhotoMOS relays, optocouplers or similar), whereby the signal lines can be influenced in a variety of ways. • Galvanically coupled attenuators (e.g. via transistors directly on the signal lines). • Coupling of the interference signal via galvanically isolating signal transmitters or transformers.

[0018] In one embodiment, an embedded spectrum analyzer, e.g. in the form of a software-defined radio (SDR), can be integrated using an unused conductor or another conductor not directly affected by the artificial interference source. Using a frequency sweep, a spectrum of the signal-to-noise ratio can be created over the frequency using a signal capacitively coupled to the actual transmission path. In addition to the signal-to-noise ratio, the frequency-dependent attenuation of the cable can also be determined in this way. The spectrum determined in this way can then be used directly for quality analysis using suitable mathematical models, since the frequency-dependent attenuation of the cable should normally hardly change: the greater the deviation between the determined spectrum and the initially determined spectrum (reference), the more serious the external influences.The reference spectrum can be stored automatically and adaptively over time or in the form of a manual "teach-in." The spectrum can also be processed using machine learning, thus automatically detecting a noticeable change in the signal path.

[0019] In one embodiment, the method can also be applied to radio connections; in this case, the transmission power is reduced and regulated until the corresponding bit error rate is achieved at the receiver (identical to the case of a cable connection). In this case, an active interference source is eliminated as a possibility.

[0020] One design provides that if an error occurs during data transmission, the transmission is repeated and the number of repetitions is monitored.

[0021] One embodiment provides that the data transmission protocol is extended by a test data packet and the disturbance is only applied to the test data packet.

[0022] One embodiment provides for the test data packet to be sent when no payload data is being transmitted. The test data packet is always sent in the context of the (artificial) interference by adapting the interference variable, while normal data transmission (the payload data) proceeds without the artificial interference. The payload data transmission is therefore subject to the signal-to-noise ratio inherent in the transmission path. The test data packet is transmitted in a test data transmission, while the payload data is transmitted in the payload data transmission. The system is therefore designed such that the test data packet is sent when it is not busy transmitting the payload data. This is one aspect of the method for checking the connection and thus the quality of the data transmission when it is not actively in use.

[0023] One embodiment provides that the test data packet includes forward error correction.

[0024] One design provides that the test data packet is announced by the data transmission.

[0025] One design provides that the disturbance variable is only switched on temporarily.

[0026] One embodiment provides that the disturbance variable is switched on cyclically or that the disturbance variable is switched on by a user.

[0027] One embodiment provides that the disturbance variable can be adjusted by capacitive coupling of an interference signal, in particular to one or more wires of the cable, by electrically adjustable attenuators, in particular optically galvanically isolated components, galvanically isolating signal transmitters or transformers, and / or by galvanically coupled attenuators.

[0028] One embodiment provides for the signal-to-noise ratio to be analyzed spectrally.

[0029] The object is further achieved by a system for carrying out the method as described above, comprising a transmitter and at least one sensor which is connected to the transmitter in particular via a cable.

[0030] This is explained in more detail using the following figures. Fig. 1 shows the claimed system. Fig. Figure 2 shows a general diagram of a control loop. Fig. Figure 3 shows a general diagram of an attenuator. Fig. 4 shows an exemplary implementation of a fault.

[0031] In the figures, identical features are identified by identical reference numerals.

[0032] The claimed system in its entirety has the reference numeral 200 and is in Fig. 1 shown.

[0033] A measuring transducer 1 - also called a transmitter - is generally a device that converts an input variable into an output variable according to a fixed relationship.

[0034] The transmitter 1 is used in the system 200. The system 200 thus comprises at least the transmitter 1 and a sensor 100. In Fig. 1, the transmitter 1 is connected to the sensor 100 via a cable 111. The raw measured values ​​of the sensor 100 are processed in the transmitter 1, for example, averaged and / or converted into another variable using a calibration model, such as the process variable to be determined, and possibly forwarded, for example, to a control system.

[0035] The sensor 100 comprises a first physical interface 103, via which the sensor 100 is connected to the transmitter 1 and exchanges data (bidirectionally) and is supplied with power (unidirectionally). The cable 111 is part of a connection element 110, which can be connected to the transmitter 1 at one end and to the sensor 100 at the other end. The cable 111 has, for example, four wires. At the sensor-side end, the cable 111 has a second physical interface 113 that is complementary to the first physical interface 103. The physical interfaces 103, 113 are designed, for example, as galvanically isolated, in particular as inductive interfaces. The physical interfaces 103, 113 can be coupled to one another via a mechanical plug connection. The mechanical plug connection is hermetically sealed, so that no liquid, such as the medium to be measured, air, or dust, can penetrate from the outside.

[0036] The sensor 100 comprises at least one sensor element 104 for detecting a process automation measured variable. The sensor 100 is then, for example, a pH sensor, also known as an ISFET, generally an ion-selective sensor, a sensor for measuring the redox potential, the absorption of electromagnetic waves in the medium, for example, with wavelengths in the UV, IR, and / or visible range, oxygen, conductivity, turbidity, the concentration of non-metallic materials, or temperature with the respective corresponding measured variable.

[0037] The sensor 100 further comprises a first coupling body 102, which comprises the first physical interface 103. The connection element 110 comprises a second, cylindrical coupling body 112, which is designed complementarily to the first coupling body 102 and which can be plugged onto the first coupling body 102 with a sleeve-shaped end portion, wherein the second physical interface 113 is plugged into the first physical interface 103.

[0038] The sensor 100 includes a data processing unit 105, such as a microcontroller, which processes the measured variable values, e.g., converting them into another data format. The data processing unit 105 is designed to be relatively small and economical in terms of computing capacity and storage volume for energy and space reasons. The sensor 100 is thus only configured for "simple" computing operations, such as averaging, preprocessing, and digital conversion. The data processing unit 105 converts the value dependent on the measured variable (i.e., the measurement signal of the sensor element 104) into a protocol understandable by the transmitter 1.

[0039] The connection element 110 may include a data processing unit 115. The data processing unit 115 is designed to be "small" and can serve as a repeater for the data.

[0040] Several sensors 100 can also be connected to one transmitter 1. In Fig. Figure 1 shows two sensors 100, only one of which is provided with all reference numerals. Identical or different sensors can be connected. The left-hand sensor is shown in the connected state. For example, up to eight sensors 100 can be connected to the transmitter 1.

[0041] Transmitter 1 is connected to a higher-level unit 120, such as a control system, via a cable 121. Transmitter 1 forwards the measurement data via cable 121 to a control system 120. The control system 120 is configured either as a process control system (PLC), PC, or server. Transmitter 1 converts the data into a data format understandable by the control system, for example, in a corresponding bus such as HART, Profibus PA, Profibus DP, Foundation Fieldbus, Modbus RS485, or an Ethernet-based fieldbus such as EtherNet / IP, Profinet, or Modbus / TCP. For this purpose, transmitter 1 has a corresponding module 4, i.e., a communication module.

[0042] The transmitter 1 comprises a display 7 and one or more operating elements 8, such as knobs or rotary knobs, buttons, or softkeys, via which the transmitter 1 can be operated. The display 7 can be used to display, for example, measurement data from the sensor 100 or information from the app 2 via the menu structure M. The sensor 100 can also be configured and parameterized via the operating elements 8 and the corresponding view in the display 7. The display 7 can also be designed as a touch display, and the operating elements 8 can then also be part of the touch display, specifically as touch operating elements. The transmitter 1 comprises a data processing unit 6 with a memory 6a. The transmitter 1 can also comprise an SD card slot 9. The transmitter 1 can also comprise one or more communication modules as modules, such as Bluetooth, mobile communications (2G, 3G, 4G, 5G), or other, possibly also wireless bus protocols such as WirelessHART.

[0043] Fig. Figure 2 shows a general diagram of a control loop. In general, control is a process in which a variable, the controlled variable y(t), is continuously recorded, compared with another variable, the reference variable w(t), and influenced to bring it into line with the reference variable. The control principle is the comparison of the setpoint / actual value of the reference variable w(t) with the negatively fed-back measured controlled variable y(t). The controller determines a manipulated variable u(t) based on the control deviation e(t) and the specified control parameters. This manipulated variable u(t) influences the controlled variable y(t) via the controlled system in such a way that the control deviation e(t) is minimized despite the presence of disturbances d(t), and the controlled variable y(t) assumes a desired time behavior depending on the selected quality criteria.

[0044] In the claimed method, the data transmission between sensor and transmitter is actively and deliberately disrupted via the disturbance variable d(t). The disturbance variable d(t) is adjusted in the control loop to achieve a constant error rate during data transmission, with the error rate being greater than 0. The disturbance variable d(t) is correlated with the signal-to-noise ratio of the data transmission. In one embodiment, the disturbance variable is proportional to the signal-to-noise ratio of the data transmission. In one embodiment, the disturbance variable and the signal-to-noise ratio of the data transmission are non-linearly related.

[0045] Fig. Figure 3 shows a general diagram of an attenuator. An attenuator R can be arranged in series or parallel. The attenuator serves to introduce a disturbance as described above.

[0046] Fig.Figure 4 shows an example implementation. Cable 111 connects sensor 100 and transmitter 1 and includes four wires with signal lines A and B, power supply VCC, and ground GND. The figure shows a disturbance caused by a PhotoMOS, reference symbol R. Transmitter 1, for example, includes an RS-485 transceiver with lines RE, Rx, Tx, and DE. List of reference symbols 1 transmitter 6 Data processing unit 6a storage 7 Display 8 controls 9 card slots 100 sensors 102 coupling body 103 Interface 104 Sensor element 105 Data processing unit 110 connecting element 111 cables 112 coupling body 113 Interface 115 Data processing unit 120 guidance system 121 cables 200 systems A signal line B Signal line GND Ground VCC supply R Attenuator t time d(t) disturbance variable e(t) control deviation u(t) manipulated variable w(t) reference variable y(t) controlled variable

Claims

[1] Method for detecting the deterioration of the quality of data transmission between a transmitter (1) and a sensor (100), in particular via a cable (111), via a control loop, where the data transmission is actively disturbed by the disturbance variable (d(t)) and the disturbance variable (d(t)) is tracked in the control loop in such a way that a constant error rate is obtained during the data transmission, where the error rate is greater than 0, where the disturbance variable (d(t)) is correlated to the signal-to-noise ratio of the data transmission, and thus to the quality of the data transmission. [2] Method according to claim 1, wherein in case of an error in the data transmission the transmission is repeated and the number of repetitions is monitored. [3] Method according to one of claims 1 or 2, wherein the data transmission protocol is extended by a test data packet and the disturbance is applied only to the test data packet. [4] Method according to the preceding claim, wherein the test data packet is sent when no payload data transmission takes place. [5] The method of claim 3 or 4, wherein the test data packet comprises forward error correction. [6] Method according to one of the preceding claims 3 to 5, wherein the test data packet is announced by the data transmission. [7] Method according to one of the preceding claims, wherein the disturbance variable (d(t)) is only temporarily switched on. [8] Method according to one of the preceding claims, wherein the disturbance variable (d(t)) is switched on cyclically or wherein the disturbance variable is switched on by a user. [9] Method according to one of the preceding claims, wherein the disturbance variable (d(t)) is adjustable by capacitive coupling of an interference signal, in particular to one or more wires (117) of the cable (111), by electrically adjustable attenuators (R), in particular optically galvanically isolated components, galvanically isolating signal transmitters or transformers, and / or by galvanically coupled attenuators. [10] Method according to one of the preceding claims, wherein the signal-to-noise ratio is spectrally analyzed. [11] System (200) for carrying out the method according to one of the preceding claims, comprising a transmitter (1) and at least one sensor (100) which is connected to the transmitter (1) in particular via a cable (111).

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