DE102017214862A1 - Detection of signal path defects in the measurement of bioelectric signals - Google Patents

Abstract

Error detection devices (40; 41; 42) for detecting signal path defects (D) in a differential voltage measurement system (1) and such a differential voltage measurement system (1) are described. This differential voltage measuring system (1) has a signal measuring circuit (2) with at least two useful signal paths (6a, 6b) for the measurement of bioelectric signals (BS). The error detection device (40) has at least one first interference signal path (7S) for measuring a first interference signal (S [k]) and a Störsignalauswerteeinheit (13; 18). The Störsignalauswerteeinheit (13, 18) serves to detect a signal path defect in at least one of the Nutzsignalpfade (6a, 6b) of the differential voltage measuring system (1). The signal path defect (D) is detected when at least a part of the bioelectric signals (BS) is measured on the first noise path (7S). In addition, corresponding methods for the detection of signal path defects (D) in a differential voltage measuring system (1) for the measurement of bioelectric signals (BS) are explained.

Description

The invention relates to an error detection device and to a method for detecting signal path defects in a differential voltage measuring system which has at least two useful signal paths and a signal measuring circuit for measuring bioelectric signals. In addition, the invention relates to a differential voltage measuring system with such an error detection device.

Differential voltage measuring systems for measuring bioelectric signals are used, for example, in medicine for the measurement of electrocardiograms (ECG), electroencephalograms (EEG) or electromyograms (EMG). In such applications, it is preferable to pay attention to a high input impedance of at least several MOhms on each measurement channel in order to reduce or at least not amplify the influence of noise. The high target input impedance should also be kept in the cables, the above-mentioned devices for the measurement of bioelectric signals. Usually, the test leads of the cables are surrounded by a shield. In addition, the cables are flexible, slim and lightweight for better manageability. However, these features conflict with the life and manageability of the cables and increase the risk of cable failure.

The cause of defective cables are, for example, broken lines or often kinks, as z. In 1 are shown. Kinks may result from torsion or flexing of the long cables when the test leads bulge out and do not return to their original shape. The bulging leads may then break the line insulation and contact the shield, which may result in reduced input impedance in the cables and hence amplification of interference. The problem here is that such interference, without a special test environment, can not always be clearly attributed to a reduced input impedance in the cables. In addition, kinks and other input impedance-reducing cable defects often occur as loose contacts, which also makes fault detection difficult. Therefore, there is a risk of unintentionally working with a defective cable until signal quality is insufficient to perform bioelectric measurements and examinations.

A common solution to avoid or detect interference from a reduced input impedance in the cables is to have the cables replaced at regular intervals, or at least inspected by service personnel. When testing the cables by service personnel, a reference signal generated by a simulator is applied to the cable under test. The cable is then moved and an output signal is measured. This output signal is compared with the reference signal and checks whether there are deviations between the two signals and thus interference. For which faults a cable break is assumed, however, is based on the expert opinion. In addition, this review is relatively expensive.

It is therefore an object of the present invention to provide an apparatus and a method for detecting signal path defects, in particular cable defects, in a differential voltage measurement system.

This object is achieved by an error detection device according to claim 1, by a differential voltage measuring system according to claim 11 and by a method according to claim 15.

The fault detection device according to the invention detects in a differential voltage measuring system mentioned above signal path defects, in particular cable defects of the cables, e.g. lead from the patient to a measuring device of the differential voltage measuring system. As explained in the introduction, this differential voltage measuring system, for example an ECG measuring system, has a signal measuring circuit with at least two useful signal paths for measuring the bioelectric signals. According to the invention, the error detection device has at least one first interference signal path for measuring a first interference signal and a Störsignalauswerteeinheit to detect a signal path defect in at least one of the Nutzsignalpfade the differential voltage measuring system. This signal path defect is detected here according to the invention, if at least part of the bioelectric signals, for. B. ECG signals, is measured on the first Störsignalpfad.

In the measurement of bioelectric signals, for example of ECG signals, common-mode interference signals, also called "common-mode" signals (CM signals), are known to occur frequently. They arise z. B. from the mains frequency with 50Hz and occur when in the differential signal measurement at the measuring inputs of the two Nutzsignalpfade uneven conditions such as different impedances and capacitances occur.

As a rule, ie with intact useful signal paths or cables, the input impedances of the test leads of the cables of an ECG measuring system are so high that the interference signal on the first Noise signal path measured is this common mode noise signals corresponds. However, the inventors have recognized that with a reduced input impedance of the cables, the potential of the differential voltage meter, e.g. As the ECG device, an increased compared to the intact cable power generated. As a result, the signal on the first interference signal path no longer contains not only common-mode interference signals, but also the bioelectric signals induced by the differential voltage measurement system.

In accordance with the invention, in the method for detecting signal path defects in the differential voltage measuring system explained above, a first interference signal is measured on a first interference signal path and evaluated by a subsequent interference signal evaluation unit. This is done to measure at least part of the bioelectric signals, i. to detect whether the bioelectrical signals (erroneously) have overcoupled from one of the useful signal paths to the Störsignalpfad. Thus, it can be detected in a simple manner whether there is a signal path defect, in particular a cable defect, on at least one of the useful signal paths of the differential voltage measuring system.

So instead of checking the useful signal paths or the cables to be tested itself, as is the case in the prior art, it is then indirectly measured on an interference signal path and searched for a useful signal, which was coupled in by an error of a useful signal path.

The advantage of the devices and methods of the invention described herein is that no technician or service personnel is needed anymore to detect a cable failure. The measurement on the Störsignalpfad can parallel and automatically during a useful signal measurement and a cable defect can be made immediately visible, for example on a user interface of the differential voltage measuring system, such as an ECG measuring system. Therefore, the signal path defect, or cable defect, immediately z. B. be discovered by the operator himself and the cable can be replaced immediately and a correct measurement can be performed. This also reduces the risk of further measurement with undetected damaged cables.

The fault detection device according to the invention can be an independent component and, for example, as a retrofit kit in existing ECGs, EEGs or EMGs via, for example, connectors installed or upstream or interposed, which will be explained later in more detail. Preferably, however, the error detection device is already firmly integrated in a differential voltage measuring system according to the invention.

Further, particularly advantageous embodiments and developments of the invention will become apparent from the dependent claims and the following description, wherein the claims of a claim category can also be developed analogous to the claims and description parts to another claim category and in particular also individual features of different embodiments or variants new embodiments or variants can be combined.

In a differential voltage measuring system mentioned above or the ECG measuring system, the signal measuring circuit generally has a first and a second electrode. The electrodes are attached to a patient to measure an electrical potential applied there. The structure of the electrodes may depend on the exact nature of the measurement, e.g. whether it is an ECG measurement, an EEG measurement or an EMG measurement and where exactly the potential should be measured on the patient. Suitable electrodes for various applications are known in the art. The output of the electrodes is, preferably via said signal measuring cable, preferably with an amplifier circuit, more preferably a differential amplifier, which detects the difference in the measured potential of the two electrodes and amplified, electrically connected. In addition, the signal measuring circuit has a signal detection unit connected at the output of the amplifier circuit in order to amplify the amplified signals or e.g. to capture the potential difference and continue to use and / or record. For example, the signal acquisition unit may include an A / D converter and a unit to further process the digital signal.

The signal measuring circuit of the differential voltage measuring system preferably has a third useful signal path. Furthermore, the signal measuring circuit comprises a driver circuit which is connected between a current measuring resistor and the signal detection unit. The driver circuit is also referred to as "Right Leg Drive" (RLD) and is responsible for generating a signal which is regulated to the average common mode voltage of each or all of the signals. The common-mode interference signals already mentioned above and measured can thereby be eliminated in the useful signal paths.

The third useful signal path (or "right leg drive path") ensures potential equalization between the patient and the differential Voltage measuring system or the ECG measuring system, wherein the electrode of the third Nutzsignalpfads is preferably mounted on the right leg of the patient, whereupon the designation "Right Leg Drive" is due. Basically, this third potential can also be recorded elsewhere on the patient.

Also, the first Störsignalpfad the fault detection device according to the invention is preferably connected via an electrode to the patient. Therefore, the third useful signal path can preferably coincide completely or at least partially with the first interference signal path, which is explained in more detail below, or at least partially correspond to it. For example, the same electrode and the same cable may be used for the third payload path and the first disturbance signal path. It is then not even necessary for the operating personnel to apply additional electrodes for the signal path check according to the invention to the patient or to perform other special measures.

The first interference signal path preferably has a current measuring unit. This current measuring unit preferably comprises a current measuring resistor, which is preferably a shunt resistor, and a voltage measuring device connected in parallel therewith.

The current measuring resistor may in this case be connected between the third electrode and the driver circuit of the signal measuring circuit, i. the right leg drive.

It is preferable that the shunt resistor has at least a resistance value of 10 kΩ and a maximum resistance value of 1000 kΩ.

The voltage measuring device is preferably also a differential amplifier. The Störsignalpfad has at the output of the voltage measuring device to a Störsignalerfassungseinheit in order to process the measured noise signal can continue. The interference signal detection unit comprises z. As an A / D converter and a unit to process the digital signal on.

For example, within the first interfering signal or a resulting or further processing signal, for. B. in the time and / or frequency range, are searched for typical features of the bioelectric signal, for example in an ECG signal after the typical RST waves.

In a particularly preferred embodiment, the error detection device has a second interference signal path for measuring a second interference signal. This Störsignalpfad can be constructed in different ways. Preferably, it may be constructed such that no bioelectric signals are injected, but other spurious signals that also occur on the first spurious signal path, such as the common mode spurious signals described above. The second interference signal path may preferably serve for a reference measurement for the interference signal on the first interference signal path.

The second interference signal path does not have to include a signal measuring cable, but may correspond to a capacitive measurement or coupling to ground.

Preferably, the second Störsignalpfad runs between a reference potential of the differential voltage measuring system or the ECG measuring system and an external reference potential, z. B. the earth potential. As mentioned, this electrical coupling is preferably via a capacitive coupling. Since the interference signal path is coupled to the differential voltage measuring system or the ECG measuring system only via the common reference potential, the second interference signal on the second interference signal path is largely independent of the input impedances of the cables used in the useful signal paths. The interference signal is therefore largely determined by common-mode noise and contains no bioelectric signals, such as ECG components.

To implement the capacitive coupling, the second interference signal path preferably has a conductor surface electrically connected to the reference potential of the differential voltage measurement system, between the differential voltage measurement system or the ECG measurement system and the ground potential. Here, the conductor surface corresponds to a coupling capacity. The conductor surface can z. B. be realized by a metal plate or foil.

The conductor area is preferably at least 3 cm ² . Preferably, the conductor area is a maximum of 10 cm ² .

The second interference signal path may also have a current measuring unit. The current measuring unit may in this case preferably be connected between the reference potential of the differential voltage measuring system, the ECG measuring system and the capacitive connection to the external reference potential of the conductor surface. Furthermore, this current measuring unit may also preferably have a current measuring resistor and a voltage measuring device connected in parallel with it. The current measuring resistor is preferably a shunt resistor and the voltage measuring device preferably by a differential amplifier.

It is preferable that the shunt resistor has at least a resistance value of 10 kΩ and a maximum resistance value of 1000 kΩ.

The Störsignalpfad can z. B. at the output of the voltage measuring device have a Störsignalerfassungseinheit.

If two Störsignalpfade be used, the Störsignalauswerteeinheit z. B. preferably be coupled between the two Störsignalerfassungseinheiten that detect the first and second interference signal. The Störsignalauswerteeinheit can then preferably be adapted to form a combination signal, preferably a difference signal, from the first and second interference signal, so as to detect bioelectric signals on the first Störsignalpfad and thus detect a signal path defect or cable defect. The difference signal is composed here of the first and second interference signal.

In a particularly preferred embodiment, the error detection device may comprise an adaptive filter which is set as a function of the first and second interference signal. In this case, the control value input of the adaptive filter is preferably supplied with the combination signal, preferably the difference signal, as a feedback value.

The application of the adaptive filter with the combination signal or difference signal serves to reduce a possible different influence of the transmission paths or their different transmission functions on the interference signals. The filtering can be part of the Störsignalauswerteeinheit.

As a combination signal, for example, a ratio of the first and second interference signal may include.

Preferably, the adaptive filter has an LMS or RLS algorithm, i. he works according to such an algorithm.

Preferably, the error detection device according to the invention has an output unit which is connected to the output of Störsignalauswerteeinheit or externally, z. B. works via a radio transmission. The output unit is used to output a detected signal path defect or to signal it the same. This output or signaling can be done on site z. B. optically, acoustically. In addition, the signaling by radio z. B. sent to a service technician. Another output form can be used as logging, z. B. done together with the measurement data. Particularly preferably, the logging is time-correlated to the measuring signal or the bioelectrical signals to be measured, so that e.g. in the case of a disturbance occurring only intermittently, as in the case of a loose contact, it is documented which measured values can be used and which are not.

In particular, when the error detection device is integrated in the differential voltage measurement system, the output unit is preferably included in a user interface of the differential voltage measurement system. Thereby, for example, the operator on the user interface, e.g. a monitor, at the same time check the bioelectric signals, such as ECG signals, and at the same time detect a cable defect.

• 1 schematisch eine Möglichkeit zur Positionierung der elektrischen Anschlüsse bzw. Kontakte eines EKG-Messsystems am Patienten,
• 2 Röntgenbilder zweier EKG-Kabel mit Kinken,
• 3 schematisch ein differentielles Spannungsmesssystem mit einer Fehlerdetektionsvorrichtung gemäß einem ersten Ausführungsbeispiel der Erfindung,
• 4 schematisch ein differentielles Spannungsmesssystem mit einer Fehlerdetektionsvorrichtung gemäß einem zweiten Ausführungsbeispiel der Erfindung,
• 5 schematisch ein differentielles Spannungsmesssystem mit einer Fehlerdetektionsvorrichtung gemäß einem dritten Ausführungsbeispiel der Erfindung,
• 6 schematisch eine Signalverarbeitungsgrafik zur genaueren Erläuterung des differentiellen Spannungsmesssystem gemäß 5,
• 7 ein Messdiagramm, das das Ausgangssignal einer Filtereinrichtung, wie sie im Zusammenhang mit den 5 und 6 erläutert wird, bei intaktem Kabel zeigt,
• 8 ein Messdiagramm, das das Ausgangssignal einer Filtereinrichtung, wie sie im Zusammenhang mit den 5 und 6 erläutert wird, bei reduzierter Eingangsimpedanz durch eine Kinke im Kabel mit Markierung der Herzschlagerkennung zeigt.

The invention will be explained in more detail below with reference to the accompanying figures with reference to embodiments. The same components are provided with identical reference numerals in the various figures. The figures are usually not to scale. Show it:

• 1 schematically a possibility for positioning the electrical connections or contacts of an ECG measuring system on the patient,
• 2 X-ray images of two ECG cables with kins,
• 3 1 schematically shows a differential voltage measuring system with an error detection device according to a first exemplary embodiment of the invention,
• 4 schematically a differential voltage measuring system with an error detection device according to a second embodiment of the invention,
• 5 schematically a differential voltage measuring system with an error detection device according to a third embodiment of the invention,
• 6 schematically a signal processing diagram for more detailed explanation of the differential voltage measuring system according to 5 .
• 7 a measurement diagram showing the output of a filter device, as in Related to the 5 and 6 is explained with intact cable shows
• 8th a measurement diagram showing the output of a filter device, as related to the 5 and 6 is shown with reduced input impedance through a kink in the cord with mark of heartbeat detection.

In the figures, each example of an ECG measuring system 1 as a differential voltage measuring system 1 assumed to be bioelectric signals BS , here ECG signals BS , to eat. However, the invention is not limited thereto.

The 1 shows an ECG measuring system 1 namely an external view of an ECG device 27 with its electrical connections and it's over cables K connected electrodes 3 . 4 . 5 to a patient P ECG signals BS to eat. This ECG measuring system 1 is by means of the invention capable of a cable defect D in one of the cables K to detect.

To the ECG signals BS At least one first electrode will be measured 3 and a second electrode 4 needed on the patient P are attached. By signal measuring cable K are the electrodes 3 . 4 over connections 25a . 25b mostly connectors 25a . 25b with the ECG device 27 connected.

A third electrode 5 serves as a reference electrode to equipotential bonding between the patient P and the ECG device 27 to accomplish. This will be explained later in more detail. Classically, this third electrode is attached to the right leg of the patient (which is why, as mentioned above, this connection is often referred to as "Right Leg Drive" or "RLD"). But it can also be positioned at a different location, as here. In addition, via further connections, which are not shown in the figures, on the ECG device 27 a large number of further contacts for further derivations (potential measurements) on the patient P attached and used for the formation of suitable signals.

Between the individual electrodes 3,4,5, the voltage potentials form UEKG ₃₄ . UEKG ₄₅ and UEKG ₃₅ for measuring the ECG signals BS serve.

The measured ECG signals BS be on a user interface 14 of the ECG device 27 displayed.

The patient P is at least capacitive with the ground potential in the ECG measurement e coupled (in 1 schematically represented by a coupling on the head and the right leg). However, it is subject to a constant disturbance source U _cm which has changed with time t, for example an electric field resulting from the 50 Hz alternating current supply, and the resulting low interference signal n _source (t), which is caused by the relatively sensitive measurement is inevitably included.

As a result of this source of interference U _cm , interfering signals are generally transmitted to the patient P on the test leads in the signal measuring cables K coupled, which will be referred to later.

The signal measuring cable K which of the electrode 3 and 4 to the EGK device 27 lead, are here part of the Nutzsignalpfade 6a . 6b , The signal measuring cable K which is from the electrode 5 to the EGK device 27 leads, this corresponds to a part of a third Nutzsignalpfads 7N , The third payload path 7N transmits interfering signals n _RLD (t) of the source of interference U _cm , which are transmitted to the patient P and the electrodes were coupled.

As previously described, the electrodes are via signal measuring cables K to the ECG device 27 connected. To the application of the ECG measuring system 1 on the patient P as simple as possible, the cables should K slim, light and at the same time shielded. However, this feature combination, as described above, often leads to cable defects D as seen on the X-ray images of two cables K that z. B. in an ECG device 27 for measuring an ECG signal BS Find application in 2 you can see. The two cables K each show a cable defect D in the form of a Kinke D , This cable defect D can after a bend or twist of the cable K arise. This can lead to an irreversible bulging of the test leads, which breaks the line insulation. By breaking the line insulation, contact between the test leads and the shield can occur S arise. This contact reduces input impedance and amplifies noise. The invention serves in particular for such described kinks D and other cable defects D to recognize.

To these cable defects D the ECG measuring system according to the invention can now be seen 1 an error detection device 40 , which will be explained later in more detail, on.

With the help of this error detection device 40 be the cables K on, for example, the cable defects described above D checked.

The fault detection device 40 generated test signal PS , which signals a cable failure, can as in 1 shown by an output unit 16 ' on the user interface 14 of the ECG device 27 be displayed and displayed. This not only allows the ECG signals BS but at the same time on the user interface 14 also the cables K on a possible cable defect D be monitored.

The output unit 16 but not necessarily integrated into the user interface. The signaling can z. B. via a signal light, for example in the form of an LED (light emitting diode) or the like, can be realized, which signals a defect. But you can additionally or alternatively acoustically z. B. via a warning tone. Another variant is also an external transmission z. B. by radio to a service technician or for output in a measurement report and so to display a cable defect or to log. In addition, the ECG device 27 as in 1 shown an external interface 15 to provide, for example, a port for a printer and / or a storage device or even a network with several such different devices.

In 3 is very roughly schematically a possible internal structure of an ECG device 27 , for example, the ECG device 27 out 1 , an ECG measuring system 1 illustrated.

The ECG measuring system 1 includes a signal measuring circuit 2 which for measuring the bioelectric signals BS serves.

The signal measuring circuit 2 has here as mentioned above three Nutzsignalpfade 6a . 6b . 7N , The payload paths are how to 1 described above the electrodes 3 . 4 . 5 , the cables K and the plug connection 25a . 25b . 25c from the patient P with the ECG device 27 electrically connected. The electrodes 3 . 4 . 5 are shown here in simplified form as an RC element and illustrate the impedance values of the useful signal paths 6a . 6b . 7N ,

The first electrode 3 and the second electrode 4 stand with the patient P in such contact, that due to a potential difference between the discharge points, where the electrodes 3 . 4 sitting on the patient, a useful signal, z. B. a "heart stream" from the electrodes 3 . 4 to an amplifier circuit 8th , z. B. an operational amplifier, is transmitted. The amplifier circuit 8th includes two inputs and is electrically connected thereto via the first and second electrodes 3,4. The output signal of the amplifier circuit 8th is sent to a signal acquisition unit 9 transmitted by the amplifier circuit 8th amplified useful signal recorded. The first payload signal path 6a in this case runs from the contact of the first electrode 3 to the patient P over the first electrode 3 to the input of the amplifier circuit 8th , The second payload path 6b runs from the contact of the second electrode 4 to the patient P over the second electrode 4 to the input of the amplifier circuit 8th ,

The related to 1 described third electrode 5 is over the cable K with a current measuring resistor 10 , hereinafter referred to as shunt resistor, electrically connected. The shunt resistor 10 is also equipped with a driver circuit 11 , which is also referred to as right leg drive, as already explained, electrically connected. The driver circuit 11 is constructed so that over the electrode 5 a reference potential is applied to the patient, which corresponds to the common-mode voltages with ECG portions. For example, this reference potential can be set in a known manner to an inverse, amplified mean value of the measurement lines.

This allows the reference potential to be set to the common mode voltage. The common-mode voltage detected with the help of the shunt resistor, in addition, is also required for further purposes, which will be explained in more detail later.

To the already mentioned cable defects D can be seen, the differential voltage measuring system according to the invention 1 to the signal measuring circuit described above 2 , in addition the fault detection device 40 on which a Störsignalpfad 7S includes.

The error detection device 40 measures the above the shunt resistance 10 decreasing voltage through a parallel to him voltage measuring device 12 , The tension measuring device 12 can be replaced by an amplifier, z. As a PGA, be realized and are so the interference signals n _RLD (t) out. That of the tension measuring device 12 so measured and amplified first interference signal n _RLD (t) is by a at the output of the voltage measuring device 12 connected Störsignalauswerteeinheit 13 processed. The Störsignalauswerteeinheit 13 For example, it can be realized by an A / D converter and a computing device with suitable software and / or by one or more ASICs (application specific integrated circuit) or the like to the interference signals n _RLD (t) to digitize and if necessary to further process and / or evaluate. In the figure, a digital interfering signal S _RLD [k] from the Störsignalauswerteeinheit 13 output. [k] corresponds here to a sequence number of a sample of the signal, thus also representing the time t only in the form of a "sample number".

As part of an evaluation, the digital interference signal S _RLD [k] z. B. in the time and / or frequency range for typical characteristics of the ECG signal are searched.

The first interference signal path 7S So here is the part of the third Nutzsignalfades 7N between the third electrode 5 , or the contact with the patient P over the third electrode 5 , to the input of the driver circuit 10 educated.

In other words, the signal path 7N . 7S comprising the third electrode 5 , the cable K as well as the further device-internal line (with the shunt resistor 10 ) to the driver circuit 11 has a double function here. They belong on the one hand to the signal measuring circuit 2 to equipotential bonding between the patient P and the ECG device 27 and to the error detection device 40 to the interference signals or common-mode interference signals and in the event of a cable defect D possible incorrectly coupled useful signals, here the ECG signals BS , capture.

The error detection device 40 but does not have, such. In 3 shown to be integrated in the ECG measuring system. It can also be installed in an already existing ECG measuring system via, for example, plug-in connections, or also upstream or in between. Such a retrofit makes it possible, even with an existing ECG measuring system cable defects D to detect.

To the ECG signals BS as well as possible cable defects D by means of a test signal PS (please refer 1 ) on the user interface 14 in parallel, this is to the signal acquisition unit 9 the signal measuring circuit 2 and to the Störsignalauswerteeinheit 13 the fault detection device 40 connected. The user interface 14 is here therefore with an output unit 16 ' shown to illustrate this possibility.

The further output unit described above 16 for example, optical and / or acoustic signaling of a cable defect D is here also with an output of Störsignalauswerteeinheit 13 coupled.

In addition, the differential voltage measuring system 1 as already mentioned with an external interface 15 For example, for a network, a printer and / or a memory etc. equipped, the z. B. with the signal detection unit 9 the signal measuring circuit 2 and / or Störsignalauswerteeinheit 13 can be connected by signal technology.

In 4 becomes a further embodiment of the differential voltage measuring system 1 or the ECG measuring system 1 similar to the one in 3 , shown. This differential voltage measuring system 1 also includes a signal measuring circuit 2 and an error detection device 41 ,

The signal measuring circuit 2 corresponds to in connection with 2 described signal measuring circuit 2 ,

The error detection device 41 represents another embodiment of the invention to the signal path defects D , or cable defects D to detect. The error detection device 41 here has two Störsignalpfade 7S . 22 on. The first interference signal path 7S includes, as in the embodiment in 2 , the third electrode 5 which with their entrance to a patient P is connected and runs up to the shunt resistor 10 that with the output of the electrode 5 electrically connected. The above the shunt resistor 10 Falling voltage is also here by the parallel to the shunt resistor 10 switched voltage measuring device 12 measured. The thus measured interference signal n _RLD (t) is then from a to the output of the voltage measuring device 12 switched Störsignalerfassungseinheit 17 digitized, further processed and recorded.

The error detection device 41 here additionally includes a second current measuring unit 19 . 20 , With this second current measuring unit 19 . 20 becomes that of an internal reference potential V of the ECG device 27 via a capacitive coupling to an external fixed reference potential e , the earth potential e , flowing current measured. In this second measured interference signal n _CM (t) Above all, these are again common-mode interference signals. The capacitive coupling between the ECG device 27 and the earth potential e is always available anyway. To a defined Störsignalpfad 22 for this interference signal n _CM (t) to provide at which the interfering signal n _CM (t) can be measured well, becomes a larger area conductor surface 23 , z. B. in the form of a metal plate or a foil, with the internal reference potential V of the ECG device 27 connected, which has a "capacitor area" against the ground potential e forms. The second current measuring unit 19 . 20 is in this second Störsignalpfad 22 between internal reference potential V and conductor surface 23 connected.

For the second current measuring unit 19 . 20 , becomes the current measurement on the second noise path 22 one between internal reference potential V and conductor surface 23 switched current measuring resistor 19 , called in the following second shunt resistor, used and connected in parallel to this voltage measuring device 20 , The tension measuring device 20 can again by an amplifier, z. B. by a PGA realized.

The measured second interference signal n _CM (t) is passed through a to the output of the voltage measuring device 20 switched Störsignalerfassungseinheit 21 recorded, z. B. digitized by an A / D converter and optionally further processed.

The first interference signal S _RLD [k] which common mode noise and at a reduced input impedance, so in a defect of the cable K or measuring lines and ECG signals (namely unintentionally overcoupled portions of the ECG signal BS ), with the second interfering signal S _CM [k] , which contains only common-mode interference signals, in a - preferably digitally operating - Störsignalauswerteeinheit 18 evaluated together. The Störsignalauswerteeinheit 18 For this purpose, it is electrically connected to the two interference signal detection units 17,21.

The Störsignalauswerteeinheit 18 This is set up to the two interference signals S _RLD [K] and S _CM [k] to process so that the common mode noise on the first Störsignalpfad 7S from there with broken cables K or test leads occurring ECG signals BS can be separated or distinguished and, consequently, a cable defect D can be detected more easily. For evaluation of the interference signals S _RLD [k] . S _CM [k] , which are digital here, can the Störsignalauswerteeinheit 18 be realized again by a computing device with suitable software and / or for example by one or more ASIC.

Preferably, the Störsignalauswerteeinheit 18 be formed so that from the two interfering signals S _RLD [k] . S _CM [k] generating an output signal in which the common mode noise on the first noise path 7S are eliminated and only the ECG signals or ECG signal components occurring in the event of a fault remain.

Part of this Störsignalauswerteeinheit 18 this can be done in a particularly preferred variant of the error detection device 42 as they are in 5 is shown with the aid of a filter device 30 will be realized. This filter device 30 filters the second interference signal S _CM [k] so that when a difference of the first and second interference signal S _RLD [k] . S _CM [k] , the resulting difference signal on an intact signal measuring cable K zero or near or substantially zero (possibly with standard measurement noise).

In the filter device 30 goes through the second interference signal S _CM [k] filtering by an adaptive filter 24 , A subsequent summing element 29 performs a difference formation of the first interference signal S _RLD [k] (which remains unchanged) and second interfering signal S _CM [k] by. The used adaptive filter 24 depends on the two interfering signals S _RLD [k] . S _CM [k] or set their difference. For this purpose, a control value input is preferred 24E which is connected to the output of the summing element 29 is connected, with the resulting difference signal ECG _AE [k] (as a combination signal ECG _AE [k]) the two interfering signals S _RLD [k] . S _CM [k] applied.

Optionally, the resulting difference signal ECG _AE [k] through a to the output of the filter device 30 coupled signal processing unit 26 further processed, z. B. smoothed, and then forms the test signal PS , Without cable defect K the signal is then no longer significant, with a cable defect K contains the test signal PS then only the through the Nutzsignalpfade 6a . 6b coupled ECG signal components (see the later explained 7 and 8th ). The signal processing unit 26 may then, for example, search for these ECG signal portions to determine if the signal is a cable defect D indicates. This evaluation can take place, for example, via a threshold value analysis or a heartbeat recognition analysis. However, a variety of other algorithms may be used, such as a pattern recognition or a Kalman filter, for the difference signal ECG _AE [k] or combination signal ECG _AE [k] evaluate. An analysis in the time or frequency domain is possible.

Other designs for the Störsignalauswerteeinheit 18 are also possible. For example, it would be another possibility, the ratio of the first interference signal S _RLD [k] and the second interfering signal S _CM [k] (as another combination signal ECG _AE [k]) to form and, for example, to use as a test signal, z. B. continue to process, evaluate, display and / or log. With a reduced input impedance of a signal measuring cable, the proportion of the common mode noise signal decreases on the first Störsignalpfad 7S and increases for it on the second Störsignalpfad 22 , As a result, the ratio of the first interference signal changes with a cable defect S _RLD [k] to second interference signal S _CM [k] , This ratio can also be determined, for example, with a suitable filter device. Again, the signal produced by the filter device by a subsequent signal processing unit as the signal processing unit explained above 26 be further processed and evaluated whether the signal is a cable defect or not.

The signal measuring circuit 2 in 5 and the other structure of the error detection device 42 correspond to the construction 3 ,

6 describes, from a signaling point of view, the process for detecting a cable defect D with the in 5 described device or the operation of the adaptive filter 24 ,

The first interference signal n _RLD (t) which is about the first shunt resistor 10 is measured and the second interference signal n _CM (t) which from the reference potential V of the ECG device 27 to earth potential e at the second shunt resistor 19 is measured, both by the same source of interference or interference signal n _source (t) caused. The source of interference in this case is, for example, the electric field which arises in the power supply with an alternating current at 50 Hz.
This common mode noise signal n _source (t) will, as in 1 described about the patient P coupled, which via the electrodes with the ECG device 27 connected is.

$${\text{n}}_{\text{CM}}\left(\text{t}\right)=\text{G}\left({\text{n}}_{\text{source}}\left(\text{t}\right)\right)$$

Because the first n _RLD (t) and the second interfering signal n _CM (t) are measured over different Störsignalpfade, but they are - despite the identical original source of interference - not identical, since the Störsignalpfade 7S , 22 different transfer functions H and G have: $${\text{n}}_{\text{RLD}}\left(\text{t}\right)=\text{H}\left({\text{n}}_{\text{source}}\left(\text{t}\right)\right)$$

$${\text{n}}_{\text{CM}}\left(\text{t}\right)=\text{G}\left({\text{n}}_{\text{source}}\left(\text{t}\right)\right)$$

Nevertheless, the two interference signals n _CM (t) . n _RLD (t) (without additional coupling of the ECG signal in the first Störsignalpfad 7S) initially strongly correlated due to the common source, as two "echoes" of the same signal.

At a reduced input impedance of a signal measuring cable K a Nutzsignalpfads 6a . 6b becomes an unintentionally over-linked share ECG _RLD (t) the ECG signal to the interference signal induced by the noise source n _RLD (t) added on the first Störsignalpfad.

The additionally coupled in the first Störsignalpfad thereby signal ECG _RLD (t) is determined by the ECG signal (in 6 With ECG (t) designated) of the patient P as well as a transfer function h _K (t) intended for the overcoupling.

It should be noted that here are all transfer functions H . H . G can be time-dependent, ie can change constantly, eg when the patient is P emotional.

The original interference signal n _RLD (t) on the first Störsignalpfad including the optionally coupled signal ECG _RLD (t) and the original interference signal n _CM (t) on the second Störsignalpfad then undergo further processing, such as a further filtering and subsequent digitization of the analog signals. The change of the signals in these stages, can be, for example, by the other transfer functions H '(t) and G '(t) describe. The transfer function H '(t) is here between the measuring point MP 3 and the measuring point MP 5 certainly. The transfer function G '(t) on the other hand, it is between the measuring point MP 4 and the measuring point MP 6 certainly.

The first interference signal S _RLD [k] Therefore results from the interference source (here the above-mentioned electric field in the room or on the patient) triggered by the noise source n _RLD (t) or common-mode interference signals as well as a cable defect D from the over-linked share ECG _RLD (t) the ECG signals modified by the transfer function of the signal processing described above. The proportion of the original interference signal n _RLD (t) of the interference signal S _RLD [k] is doing by the transfer function H "(t) (formed by the chain of the first transfer function H (t) before the coupling and the further transfer function H '(t) after coupling in the ECG signal component) and is displayed between the measuring points MP 1 and MP 5 certainly.

The second interference signal S _CM [k] contains essentially only from the source of interference, here the electric field, induced interference signals _Cm (t) or common-mode noise and passes through the signal processing described above. The interference signal S _CM [k] is through the transfer function G "(t) mapped (formed by the chain of the first transfer function G (t) and another transfer function G '(t)) and will be between the measuring points MP 2 and MP 6 certainly.

It should be noted that these transfer functions are only intended to form a picture for better understanding and the measurement points MP1 , ..., MP6 not really have to exist. For example, there is a real separation between the first transfer function H (t) . G (t) and the further transfer function H '(t), G' (t) difficult.

The two original interference signals n _RLD (t) and n _CM (t) are by the same source of interference n _source (t) as mentioned strongly correlated. Therefore, the proportion of the interference signal can be S _RLD (t) in the interference signal S _RLD [k] the first Störsignalpfads 7S at the entrance of the filter device 30 with the adaptive filter 24 almost completely by an (imaginary) transfer function F (n _CM (t) ).

This transfer function F (n _CM (t) ) makes the differences between the transfer function G "(t) on the second Störsignalpfad 22 and the transfer function H "(t) on the first Störsignalpfad 7S from. For better intuition, this transfer function F (n _CM (t) ) in 6 entered. This could be determined eg between the measuring points MP5 and MP6.

The transfer function F (n _CM (t) ) is also time-dependent, ie not always the same, because the Couplings of the interfering signals do not always run the same way but different on patients P , Electrodes and shielding S acts.

To the current transfer function F (n _CM (t) ) and the interfering signal on the second interfering signal path 22 to the - not by a broken cable K caused - proportion of the signal S _CM [k] in the interference signal S _RLD [k] on the first Störsignalpfad 7S as well as possible and thus completely as possible in the output noise signal ECG _AE [k] , so the actual test signal PS , to eliminate, becomes an adaptive filter 24 used. This filter 24 is as mentioned above on the control value input 24E the output signal of the summing element 29 , ie the output noise signal ECG _AE [k] , fed back.

With intact cables K the signal measuring circuit is the output signal ECG _AE [k] behind the summator 29 apart from the measurement noise, almost zero. An example of this signal is in 7 to recognize. In the graph shown is the amplitude ECG _AE [k] plotted in mV over time t per sample k. This signal can eg as a test signal PS below the ECG signal or bioelectrical signal to be measured BS on a display unit of the ECG device 27 be shown (see 1 ), so that the operator sees immediately, if a cable defect is present and the current measurement could be falsified.

In a signal path defect of a Nutzsignalpfades 6a . 6b namely as described an ECG signal ECG _RLD (t) to the source of interference U _CM resulting first interference signal n _RLD (t) added. Because the ECG signal ECG _RLD (t) and the interfering signal n _CM (t) are very uncorrected to each other, the proportions of the ECG signal ECG _RLD (t) not with filtered out. This will contain the signal ECG _AE [k] still clearly the ECG signals. An example of one ECG _AE [k] Signal with defective cable K is in 8th shown. In the graph shown is again the amplitude ECG _AE [k] in mV over time t per sample k applied.

The error detection devices according to the invention 40 . 41 . 42 allow it, so a cable defect D in an ECG system 1 be able to detect immediately and clearly. For this, a separate test procedure does not have to be carried out by a trained service technician. Checking the cables K runs simultaneously with the ECG measurement and can be quickly and easily detected by any operator of the ECG device.

It is finally pointed out once again that the devices and methods described in detail above are merely exemplary embodiments which can be modified by the person skilled in the art in various ways without departing from the scope of the invention. Thus, the differential voltage measurement system may not only be an ECG device, but also other medical devices that detect bioelectrical signals, such as EEGs, EMGs, etc. Furthermore, the use of the indefinite article includes "on" or "off". a "does not exclude that the characteristics concerned can also be present multiple times. Similarly, the term "unit" does not exclude that it consists of several components, which may also be spatially distributed.

LIST OF REFERENCE NUMBERS

1

differential voltage measuring system / ECG measuring system

2

Signal measurement circuit

3

first electrode

4

second electrode

5

third electrode

6a, 6b

useful signal paths

7N

third payload signal path

7S

first Störsignalpfad

8th

amplifier circuit

9

Signal detection unit

10

Current sense resistor

11

driver circuit

12

Voltage measuring device

13

Störsignalauswerteeinheit

14

User interface

15

external interface

16, 16 '

output unit

17

Störsignalerfassungseinheit

18

Störsignalauswerteeinheit

19

Current sense resistor

20

Voltage measuring device

21

Störsignalerfassungseinheit

22

second Störsignalpfad

23

conductor surface

24

adaptive filter

24E

Control value input of the adaptive filter

25a

first plug connection

25b

second plug connection

25c

third plug connection

26

Signal processing unit

27

Measuring device / ECG device

28

filtering device

29

summing

30

filtering device

40, 41, 42

Error detection devices

BS

Bioelectric signals

D

Kinke

e

earth

ECG (t)

ECG signal

ECG _RLD (t)

ECG signal after passing through a signal measuring cable h _K (t) Signal in the signal measuring cables, from patient to ECG device

ECG _AE [K]

Combination signal / over-coupled component of the ECG signal

F (n _CM (t)

Transfer function (maps the differences between the transfer function G "(t) on the second interference signal path 22 and the transfer function H" (t) on the first interference signal path 7S)

G (t)

Transfer function (the measurement on the first interference signal path)

G '(t)

Transfer function (the measurement on the first interference signal path after filtering of the second interference signal and in the event of a cable defect of an input of the ECG signal)

H (t)

Transfer function (the measurement on the first interference signal path)

H '(t)

Transfer function (the measurement on the first interference signal path after filtering the first interference signal)

G "(t)

Total transfer function of G '(t) and G (t)

H "(t)

Total transfer function of H '(t) and H (t)

K

electric wire

K

sample

MP 1

Measuring point 1

MP 2

Measuring point 2

MP 3

Measuring point 3

MP 4

Measuring point 4

MP 5

Measuring point 5

MP 6

Measuring point 6

n _RLD (t)

first interference signal

n _CM (t)

second interference signal

n _Source (t)

interference source

P

patient

PS

test signal

S

shielding

T

Time

U _CM

interference source

UEKG ₃₅ , UEKG ₃₄ , UEKG ₄₅

ECG voltage sources

S _RLD [k]

first interference signal (after digitization)

S _CM [k]

second interference signal (after digitization)

V

Potential of the ECG component

Claims (15)

Error detection device (40; 41; 42) for detecting signal path defects in a differential voltage measurement system (1), which differential voltage measurement system (1) comprises a signal measurement circuit (2) for measuring bioelectric signals having at least two useful signal paths (6a, 6b), wherein the error detection device (40) has at least one first interference signal path (7S) for measuring a first interference signal (S _RLD [k]) and a Störsignalauswerteeinheit (13; 18), which is adapted to a signal path defect D in at least one of the Nutzsignalpfade (6a, 6b) of the differential voltage measuring system (1) when at least a part of the bioelectric signals is measured on the first interference signal path (7S). Error detection device after Claim 1 wherein the first Störsignalpfad (7S) comprises a current measuring unit (10, 12), wherein preferably the current measuring unit (10, 12) comprises a current measuring resistor (10) with a parallel-connected voltage measuring device (12). Error detection device after Claim 1 or 2 comprising a second interfering signal path (22) for measuring a second interfering signal (SCM [k]). Error detection device after Claim 3 , wherein the second Störsignalpfad (22) between a reference potential (V) of the differential voltage system (1) and an external reference potential (E) extends, preferably via a capacitive coupling. Error detection device after Claim 4 in which the second interference signal path (22) for forming a capacitive coupling between the reference potential (V) of the differential voltage system (1) and the external fixed reference potential (E) has a conductor surface (B) electrically connected to the reference potential (V) of the differential voltage system (1). 23). Error detection device according to one of Claims 3 to 5 wherein the second Störsignalpfad (22) comprises a current measuring unit (19, 20), wherein the current measuring unit (19, 20) preferably comprises a current measuring resistor (19) and a parallel-connected voltage measuring device (20). Error detection device according to one of Claims 3 to 6 , wherein the Störsignalauswerteeinheit (18) is adapted to a combination signal (ECG _AE [k]), preferably a difference signal (ECG _AE [k]), the first interference signal (S _RLD [k]) and the second interference signal (SCM [k ]) to build. Error detection device according to one of Claims 3 to 7 comprising an adaptive filter (24) which is adjustable as a function of the first interference signal (S _RLD [k]) and the second interference signal (S _CM [k]), preferably a control value input (24E) of the adaptive filter having the combination signal (24). ECG _AE [k]), preferably differential signal (ECG _AE [k]), the first interference signal (S _RLD [k]) and the second interference signal (S _CM [k]) is applied. Error detection device after Claim 8 wherein the adaptive filter (24) operates with an LMS or RLS algorithm. An error detection apparatus according to any one of the preceding claims, comprising an output unit (16, 16 ') for outputting a detected signal path defect. Error detection device after Claim 10 wherein the output unit (16 ') is included in a user interface (14). Differential voltage measuring system (1) having at least one signal measuring circuit with two useful signal paths (6a; 6b) (2) for measuring bioelectric signals (BS) and with an error detection device (40; 41; 42) according to one of the preceding claims. Differential voltage measuring system after Claim 12 wherein the signal measuring circuit (2) comprises a first electrode (3) and a second electrode (4), which are connected at the output to an amplifier circuit (8) and a signal detection unit (9) at the output of the amplifier circuit (8). Differential voltage measuring system after Claim 12 or 13 wherein the signal measuring circuit (2) has a third Nutzsignalpfad (7N) and a driver circuit (11), preferably a right leg drive, wherein preferably the third Nutzsignalpfad (7N) at least partially corresponds to the first Störsignalpfad (7S). Method for detecting signal path defects in a differential voltage measuring system (1) for measuring bioelectric signals (BS), wherein the bioelectric signals (BS) by means of a signal measuring circuit (2) having at least two Nutzsignalpfaden (6a, 6b) and are measured, wherein in addition at least a first interference signal (S _RLD [k]) on at least a first Störsignalpfad (7) measured and by a Störsignalauswerteeinheit (13) is evaluated, and a signal path defect (D) in at least one of Nutzsignalpfade (6a, 6b) of the differential voltage measuring system (1) is detected when at least a portion of the bioelectric signals (BS) on the first Störsignalpfad (7S ) is measured.

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