Monitoring device for a two-wire line, hazard alarm system with the monitoring device

Abstract

Monitoring device for a two-wire line (7, 9), wherein a voltage source (2) is connected to at least one functional element (3, 4, 5) via the two-wire line (7, 9), so that a useful signal is transmitted and / or can be transmitted via the two-wire line (7, 9), with a coupling device (12) different from the voltage source (2) for coupling a test signal into the two-wire line (7, 9) at the beginning of a test section of the two-wire line (7, 9), with a decoupling device (13) different from the voltage source (2) for decoupling the test signal at the end of the test section, and with an evaluation device (14) for evaluating the coupled-out test signal, wherein the evaluation is used to determine a state of the two-wire line (7, 9), wherein the test signal has an alternating current component and / or an alternating voltage component, and that the coupling device (12) is connected to a first terminal (6) of the two-wire line (7, 9) on the voltage source (2) and / or that the decoupling device (13) is connected to a second terminal (8) of the two-wire line (7, 9) on the voltage source (2), wherein the useful signals have a switching frequency in a low-frequency range and the test signal has an alternating current / voltage component in a higher-frequency range of a frequency spectrum.

Description

State of the art

[0001] The invention relates to a monitoring device for a two-wire line, wherein a voltage source is connected to at least one functional element via the two-wire line, so that a useful signal is transmitted and / or can be transmitted via the two-wire line, with a coupling device for coupling a test signal into the two-wire line at the beginning of a test section of the two-wire line, with a coupling-out device for coupling out the test signal at the end of the test section, and with an evaluation device for evaluating the coupled-out test signal, wherein the evaluation is used to determine a state of the two-wire line.

[0002] Public or private buildings, industrial facilities, train stations, airports, and the like are usually equipped with hazard warning systems that allow visitors to these locations to trigger a signal in the event of an emergency. This signal is then forwarded, for example, to a monitoring center for further processing there. Other possible tasks of the hazard warning system include alerting visitors to hazards, emergencies, or escape routes using visual, acoustic, or haptic signals. To ensure the error-free operation of hazard warning systems, the regulations to be observed in hazard warning technology and safety technology are continually adapted to the findings obtained from the operation of the hazard warning systems. One requirement of the regulations concerns the detection of changes in the condition of hazard warning system lines before these changes in condition can lead to malfunctions in the hazard warning systems.

[0003] The terms "creeping short" and "creeping open", familiar from the Anglo-Saxon language, were introduced in German as "schleichender Kurzschluss" and "schleichende Ausbruch" (creeping short circuit) and "schleichende Ausbruch" (creeping open interruption). In the specialist world, the term "creeping short circuit" refers to a slowly progressive reduction in the resistance between two wires, e.g. in two-wire cables, while "creeping interruption" refers to a slowly progressive increase in the line resistance of one, two or more wires, e.g. in two-wire cables. Environmental influences, primarily moisture and gases, which lead to the oxidation of contact points on the copper wires or to a reduction in the insulating properties between the copper wires, can be identified as the cause of these slow changes.

[0004] A monitoring system that could potentially be used to detect these changes in the condition of lines is proposed in published patent application DE 195 38 754 A1, which concerns a method for monitoring primary lines and arguably represents the closest prior art. The document describes a method for monitoring a primary line in a hazard alarm system, wherein the primary line has a detector resistor and a reference resistor connected in series. Possible malfunctions of the primary line are determined by evaluating the quotient of the voltage drop across the reference resistor and the voltage drop across the primary line or the detector resistor.

[0005] From DE 198 05 722 A1 a method for monitoring electrical lines for short circuits is known, in which a differential voltage different from zero is applied at least temporarily between the lines carrying switching signals, the actual differential voltage between two lines is determined essentially continuously and a fault detection signal representative of a short circuit between these two lines is generated if the measured differential voltage curve or the measured differential voltage deviates from a predetermined reference voltage curve or a predetermined reference voltage.

[0006] From DE 20 38 795 A a device for line monitoring of fire alarm systems is known in which one or more groups of fire detectors, which fire detectors supply a quiescent current in normal operation and an alarm current in the event of an alarm, are connected in parallel to one another in each group via common lines to a signalling centre with a supply voltage source, which groups of fire detectors supply a quiescent current in normal operation and an alarm current in the event of an alarm, which lines are terminated by a terminal element in at least one detector group, wherein at least one of the terminal elements is designed to actively generate a signal or signals with a current or voltage curve which is different from the supply voltage and the detector quiescent and alarm current when the supply voltage arrives via the lines and to transmit them to the lines, and wherein the signalling centre has a device for checking the arrival of the signals generated by the terminal element via the lines.

[0007] From DE 43 25 732 A1 a method for potential-free monitoring of a ring line used for message transmission between alarm points and a message receiving point in hazard alarm systems or fire alarm systems or transmission systems for hazard alarm systems is known, in which a signal generated by the AC voltage source is fed in via a first isolating transformer, which signal an evaluation circuit evaluates in conjunction with a second isolating transformer looped in at any point with regard to line state changes.

[0008] EP 0 111 178 B1 discloses a monitoring system with several detectors arranged in a chain along a detection line, which are connected to a control center with an evaluation unit, in each of which a series switch is opened by a jump in the interrogation voltage generated by the control center to a first value, and the series switch switches through to the next detector or to the next control unit by a jump in the same interrogation voltage to a second value and after a time determined by the detector state, wherein an electronic circuit part generates electrical signals with time intervals characterizing the detector state and passes them to the evaluation unit. To monitor the electronic circuit part, the electrical signals in the evaluation unit are compared with a time pattern that has time ranges for specific detector states and intervals between the time ranges.

[0009] DE 692 06 750 T2 discloses a filter for attenuating high-frequency noise. Disclosure of the invention

[0010] According to the invention, a monitoring device for a two-wire line with the features of claim 1 and a hazard warning system with the features of claim 12 are proposed. Preferred or advantageous embodiments of the invention emerge from the dependent claims, the following description and / or the attached figure.

[0011] The proposed monitoring device is suitable and / or designed for a two-wire line of a monitoring system. The two-wire line is preferably designed as a parallel line with two wires, wherein the two wires of the two-wire line are mechanically connected to one another over their entire length, and / or as a twisted two-wire line, wherein the two wires of the two-wire line are twisted together, and / or as a shielded two-wire line, wherein the two wires of the two-wire line are shielded by a hose-like, conductive sheath. The two-wire line serves to connect a voltage source to at least one functional element, wherein the voltage source provides a useful signal, which is preferably designed as a direct voltage for supplying the functional element, as a communication signal for the functional element, and / or for outputting a monitoring signal for the functional element.The useful signal is transmitted between the voltage source and the functional element via exactly the two wires of the two-wire cable or via at least the two wires of the two-wire cable.

[0012] The monitoring device comprises a coupling device for coupling a test signal into the two-wire line, in particular into a first wire of the two-wire line, wherein the coupling device is arranged such that the test signal is coupled at the beginning of a test section of the two-wire line. Furthermore, the monitoring device comprises a decoupling device arranged for decoupling the test signal at one end of the test section of the two-wire line, in particular at a second wire of the two-wire line.

[0013] An evaluation device is used to evaluate the extracted test signal, which can be used to determine whether a malfunction of the two-wire line is present. A malfunction particularly includes cases of a creeping short circuit and / or a creeping open circuit, for which the definition is provided in the introduction.

[0014] According to the invention, the test signal comprises an alternating current component and / or an alternating voltage component. The test signal can thus exhibit a time-varying profile, with the current or voltage amplitude exhibiting a change in sign over time. In particular, the test signal is symmetrical, so that the component of the test signal with one polarity is equal to the component of the test signal with the other polarity. In an alternative embodiment, the test signal comprises an offset onto which the alternating current component or the alternating voltage component is modulated.

[0015] The invention is based on the consideration that it is prone to errors, particularly in detecting gradual deteriorations in the condition of two-wire lines in hazard warning systems, since these lines often carry the power supply, communication signals, or monitoring signals, even in combined applications. The resulting temporal changes in voltage or current amplitudes in the two-wire lines make it virtually impossible to attribute the occurrence of a gradual short circuit, for example, to an increase in the supply current or voltage, since the increase could just as easily result from a change in the switching state of a functional element. It is equally unreliable to detect the occurrence of a gradual interruption based on a decrease in current or voltage.Detection is also made more difficult by the fact that when gradual changes occur, the functionality of the alarm system will initially be little affected. Whether a change in the supply current or voltage is even noticeable depends heavily on the location of the gradual change, for example.

[0016] The invention proposes a solution that enables early detection of the described deviations from the target state of two-wire lines, without interaction with the current or voltage supply of the functional elements supplied via the two-wire line. The invention exploits the fact that the useful signals operate at a switching frequency in a low-frequency range, whereas the test signal has an alternating current or voltage component located in a higher-frequency range of the frequency spectrum. By distributing the two signals into two different, in particular non-overlapping or only slightly overlapping, frequency bands, it is achieved that the test signal can be easily filtered out or attenuated upstream of the functional elements, and that only the test signal and not the useful signal is extracted by the extraction device.

[0017] In a preferred embodiment, the maximum of the frequency distribution of the wanted signal is located at a lower frequency than the maximum of the frequency distribution of the test signal. This makes it easy to separate the test signal from the wanted signal, or vice versa, by using a filter with a cutoff frequency located between the two maxima.

[0018] It is particularly preferred if the useful signal is embodied as a DC voltage signal for power supply, monitoring, and / or communication. In this context, a DC voltage signal is preferably understood as a signal that may exhibit temporal changes, such as the change from one switching state to the next, but preferably does not change polarity.

[0019] In general, the AC component or voltage component of the test signal can be arbitrarily configured, for example, as noise, in particular statistical or binary noise. However, it is preferred that the test signal has a regular, in particular sinusoidal or triangular, temporal amplitude curve. Such an amplitude curve simplifies the separation of the wanted and test signals using simple electronic components, such as inductors or coils.

[0020] In a particularly preferred embodiment, the coupling device and / or the decoupling device are designed for contactless, inductive, galvanically isolated, and / or potential-free transmission of the test signal. In particular, insulation or the like of the two-wire lines need not be damaged, thus eliminating the risk of the two-wire line being impaired in its function by the installation of the monitoring device.

[0021] In a preferred embodiment, the coupling device is arranged at a first terminal of the two-wire line, in particular at one of the wires of the two-wire line at the voltage source or in the immediate vicinity thereof, in particular without the interposition of further functional elements. Alternatively or additionally, the decoupling device is connected to a second terminal of the two-wire line, in particular at another wire of the two-wire line at the voltage source, in particular in the same way as the coupling device. This embodiment ensures that the entire course of the two-wire line is designed as a test section and is monitored. In addition, the monitoring device can be easily arranged centrally at the voltage source and / or in a common housing with the voltage source, so that, for example, the additional laying of cables for the monitoring device is not necessary.

[0022] In a suitable further development of the invention, a terminating resistor is connected in parallel to the at least one functional element, which is preferably designed to close an alternating current circuit between the coupling device and the decoupling device. This terminating resistor ensures, in particular, that a defined alternating current flows through the alternating current circuit. It is preferably assumed that the internal resistance of the voltage source represents a short circuit or approximately a short circuit for the frequency of the alternating current component used.

[0023] In a comparatively complex embodiment of the invention, the evaluation is performed by comparing the extracted test signal and / or its characteristics with the injected test signal and / or its characteristics. This may involve, for example, calculating a transfer function for the test section and evaluating changes in the transfer function, calculating a correlation, or similar.

[0024] A comparatively simple and therefore cost-effective alternative involves evaluating the current flow and / or voltage of the extracted test signal in its current state with an initial value of the initial current flow and / or voltage in the intact and tested monitoring system. For example, the initial value is stored as a digitized variable in a suitable storage medium, with continuous comparisons of the current value with the stored value being performed during operation. In principle, it is thus possible to evaluate the extracted test signal using an absolute evaluation or a relative evaluation.

[0025] Particularly in the latter alternative, it is preferred that the evaluation device has evaluation logic, which is embodied, for example, as software, wherein a reduction in the value of the current flow and / or the voltage of the output test signal indicates a creeping interruption and / or an increase in the value of the current flow and / or the voltage of the output test signal indicates a creeping short circuit. Thus, the type of line change can be determined from the deviation in the current flow and / or the voltage, and appropriate service measures can be initiated. The evaluation is preferably carried out in a computing unit, e.g. a microprocessor, which is usually used in the monitoring systems and / or is already present and is expanded by the monitoring device with additional functionality.

[0026] In a practical implementation of the monitoring device, a filter is connected upstream of one, several, or each functional element to filter out or at least attenuate the test signal. In the simplest and therefore preferred case, the filter is designed as an inductor, in particular a coil, wherein the filter is configured to have a high impedance or a local and / or global impedance maximum for the frequency of the AC component and / or the AC voltage component of the test signal.

[0027] Another subject of the invention relates to a hazard detection system with a two-wire line, having the feature of claim 13, which comprises a monitoring device as just described or according to the preceding claims for monitoring the two-wire line. The hazard detection system is preferably designed like the hazard detection system described above, with the functional elements being designed, for example, as detectors, in particular manual call points, fire detectors, emergency call detectors, sensors, in particular for fire, smoke, water, or noise, or displays, in particular for emergency exits. A design as an alarm system is also within the scope of the invention. Short description of the drawings

[0028] Further features, advantages, and effects of the invention will become apparent from the following description and the figure of a preferred embodiment of the invention. It shows: Fig. 1 a schematic circuit diagram of a hazard warning system as an embodiment of the invention. Embodiment(s) of the invention

[0029] The Fig. 1 shows a schematic block diagram of a hazard warning system 1, which is designed, for example, as a fire alarm system, police emergency call system, alarm system or the like.

[0030] The hazard alarm system 1 has a voltage source 2 that supplies functional elements 3, 4, and 5 with voltage or communication signals. The functional elements 3, 4, and 5 can be designed as detectors, display units, or sensor units. The voltage source 2 is implemented as a DC voltage source, so that time-varying voltage levels only occur due to changes in the switching states of the functional elements 3, 4, or 5 or due to the communication signals. The voltage source 2 has an output 6, which is connected to the functional elements 3, 4, and 5 via a first wire 7. In addition, the voltage source 2 has an input 8, which is also connected to the functional elements 3, 4, and 5 via a second wire 9, so that they are arranged in parallel. The wires 7 and 9 are preferably designed together as a two-wire line.

[0031] The components of the hazard alarm system 1 presented so far are sufficient for functionality. However, deterioration of the two-wire line, particularly of wires 7 and 9, can occur during operation. One possible source of deterioration is so-called creeping interruptions, which are visualized in the first wire 7 with the dashed line 10, whereby a creeping interruption is a slowly progressive increase in the line resistance. Of course, creeping interruptions can occur in one of the two wires 7 and 9, or in both. Another possible source of error, which is usually difficult to detect, is the so-called creeping short circuit, which is caused by a short-circuit line 11 in the Fig.1, where a creeping short circuit is understood to be a slowly progressive reduction in the resistance between the two wires 7 and 9. Of course, in addition to the gradual changes, sudden changes can also lead to a functional failure of the hazard alarm system 1.

[0032] To detect such or further functional deteriorations of the two-wire line or of the wires 7 and 9, a coupling device 12 is arranged in the area of ​​the output 6, which inductively couples a test signal, which is either in the form of an alternating voltage or current signal or at least has an alternating voltage or current component, into the first wire 7 without contact. The coupling device 12 is designed, for example, as a transmitter, wherein a transmitter represents a transformer that is not primarily designed for energy but for information transmission. The test signal is designed, for example, as a sinusoidal or triangular signal. In addition, a decoupling device 13 is arranged in the area of ​​the output 8, which can also be designed as a transmitter.This decoupling device 13 decouples the test signal, which has now passed through a test section of the two-wire line located between the coupling device 12 and the decoupling device, and feeds it to an evaluation unit 14. To prevent the test signal from interfering with the functional elements 3, 4, and 5, an inductor 15, 16, and 17 is connected in series upstream of the functional elements 3, 4, and 5, respectively. The inductors are tuned to have a high impedance for the test signal frequency used. Alternatively, the inductors 15, 16, and 17 can be connected together in a common inductor (not shown).

[0033] In order to ensure a defined alternating current flow through the test section, a terminating resistor 18 is provided, which is connected in parallel to the modules, each of which is formed from a functional element 3, 4 or 5 and one of the inductors 14, 15 or 16, wherein the terminating resistor 17 closes the alternating current path between the coupling device 12 and the decoupling device 13.

[0034] The extracted test signal is examined by the evaluation device 14, whereby various evaluation strategies are conceivable: A first possible evaluation strategy consists in comparing the extracted test signal with the injected test signal. Another possible evaluation strategy consists in comparing the amplitude of the extracted test signal with a stored amplitude and, if the amplitude changes, inferring that there is deterioration or malfunction of the wires 7 or 9. A classification of the poor function or malfunction can, for example, be such that a reduction in the amplitude of the extracted test signal indicates a gradual interruption, and an increase in the amplitude of the extracted test signal indicates a gradual short circuit. After the evaluation orClassification, the evaluation device is optionally designed to emit a warning signal.

Claims

[1] Monitoring device for a two-wire line (7, 9), wherein a voltage source (2) is connected to at least one functional element (3, 4, 5) via the two-wire line (7, 9), so that a useful signal is transmitted and / or can be transmitted via the two-wire line (7, 9), with a coupling device (12) different from the voltage source (2) for coupling a test signal into the two-wire line (7, 9) at the beginning of a test section of the two-wire line (7, 9), with a decoupling device (13) different from the voltage source (2) for decoupling the test signal at the end of the test section, and with an evaluation device (14) for evaluating the coupled-out test signal, wherein the evaluation is used to determine a state of the two-wire line (7, 9), wherein the test signal has an alternating current component and / or an alternating voltage component, and that the coupling device (12) is connected to a first terminal (6) of the two-wire line (7, 9) on the voltage source (2) and / or that the decoupling device (13) is connected to a second terminal (8) of the two-wire line (7, 9) on the voltage source (2), wherein the useful signals have a switching frequency in a low-frequency range and the test signal has an alternating current / voltage component in a higher-frequency range of a frequency spectrum. [2] Monitoring device according to claim 1 or 2, characterized by that a maximum of a frequency distribution of the useful signal is smaller than a maximum of a frequency distribution of the test signal. [3] Monitoring device according to claim 1 or 2, characterized bythat the useful signal is designed as a DC voltage signal for power supply, monitoring and / or communication. [4] Monitoring device according to one of the preceding claims, characterized by that the test signal has a sinusoidal or triangular time course. [5] Monitoring device according to one of the preceding claims, characterized by that the coupling device (12) and / or the decoupling device (13) is / are designed for inductive and / or contact-free and / or potential-free and / or galvanically isolated transmission of the test signal. [6] Monitoring device according to one of the preceding claims, characterized by that a terminating resistor (18) is connected in parallel to the at least one functional element (3, 4, 5). [7] Monitoring device according to one of the preceding claims, characterized bythat the evaluation is carried out by comparing the extracted test signal and / or its characteristics with the injected test signal and / or its characteristics. [8] Monitoring device according to one of the preceding claims, characterized by that the evaluation is carried out by comparing a current flow of the extracted test signal with a reference value. [9] Monitoring device according to one of the preceding claims, characterized by that the evaluation device (14) has an evaluation logic, wherein a reduction in the current flow leads to a conclusion about a creeping interruption and / or an increase in the current flow leads to a conclusion about a creeping short circuit. [10] Monitoring device according to one of the preceding claims, characterized by that a filter for filtering out or attenuating the test signal is connected in front of the, some or each functional element (3, 4, 5). [11] Monitoring device according to one of the preceding claims, characterized by in that an inductance (15, 16, 17) for filtering out or attenuating the test signal is connected in front of the, some or each functional element (3, 4, 5), wherein an alternating current resistance of the inductance (15, 16, 17) is adapted to a frequency of the test signal. [12] Two-wire alarm system (7, 9), characterized by that a monitoring device according to one of the preceding claims is provided for monitoring the two-wire line (7, 9).

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