CN216294062U

CN216294062U - Signal measurement circuit in differential voltage measurement system and differential voltage measurement system

Info

Publication number: CN216294062U
Application number: CN202120586932.4U
Authority: CN
Inventors: 乌尔里克·巴策尔; 马蒂亚斯·布鲁姆哈德
Original assignee: Siemens Healthineers AG
Current assignee: Siemens Healthineers AG
Priority date: 2020-03-24
Filing date: 2021-03-23
Publication date: 2022-04-15
Anticipated expiration: 2031-03-23
Also published as: DE202020101579U1

Abstract

The utility model relates to a signal measuring circuit (30) in a differential voltage measuring system (1) for measuring a bioelectric signal (S (k)) by means of a plurality of active signal paths (6a, 6b) each having a sensor electrode (3, 4). The signal measurement circuit (30) comprises: -a measurement amplifier circuit (27) for each sensor electrode (3), -one sensor line (6a) each between the measurement amplifier circuit (27) and the sensor electrode (3, 4), -a highly insulating discharge switch (31) at the input (27a) of the measurement amplifier circuit (27), which discharge switch electrically connects the sensor line (6a) with the ground line (E). The utility model further relates to a differential voltage measuring system (1).

Description

Signal measurement circuit in differential voltage measurement system and differential voltage measurement system

Technical Field

The utility model relates to a signal measuring circuit in a differential voltage measuring system for measuring bioelectrical signals by means of a plurality of active signal paths each having a sensor electrode. Furthermore, the utility model relates to a differential voltage measurement system.

Background

Voltage measurement systems, in particular differential voltage measurement systems, for measuring bioelectric signals are used, for example, in medicine for measuring Electrocardiograms (EKG), electroencephalograms (EEG) or Electromyograms (EMG). In such applications, a high input impedance of at least a few megaohms should preferably be noted on each measurement channel in order to reduce or at least not enhance the effect of interference.

The measurement of the heart activity by means of the mentioned voltage measurement system is necessary in particular for imaging of the heart in order to adapt the imaging process to the strongly pronounced movement of the heart during the heartbeat. For this purpose, conventional sensors are used which have to be fastened to the body of the patient. One possibility for heartbeat measurement is capacitive EKG, where the EKG signal is intercepted purely capacitively without the patient being in direct contact with the sensor.

The problem here is the interference caused by the process of generating electricity and tribocharging in the clothing of the patient or between the sensor and the patient. For example, the rubbing of clothing against the patient's body may generate static electricity.

SUMMERY OF THE UTILITY MODEL

It is therefore an object of the present invention to reduce or even avoid the interference that occurs when capacitively measuring bioelectrical signals.

This object is achieved by a signal measuring circuit according to the utility model and by a differential voltage measuring system according to the utility model.

The signal measuring circuit according to the utility model in a differential voltage measuring system for measuring a bioelectrical signal by means of a plurality of active signal paths each having a sensor electrode has: a measurement amplifier circuit for each sensor electrode; a sensor line between the measurement amplifier circuit and the sensor electrode; and a high-isolation discharge switch at an input of the measurement amplifier circuit, the discharge switch electrically connecting the sensor line with the ground line. The discharge switch is preferably arranged at the non-inverting input, also referred to as the positive input, of the measurement amplifier circuit. The measuring amplifier circuit preferably comprises an operational amplifier, which is designed as a so-called follower. I.e. the negative input, also called inverting input, of the operational amplifier is coupled to the output of the operational amplifier, thereby creating a high virtual input impedance at the positive input.

The high-insulation discharge switch can realize the discharge of the electrostatic charge generated by the change of the clothes and the random movement of the patient. The ground line should make it possible to discharge the sensor electrode and not only to achieve a potential balance between the individual components of the signal measurement circuit, as is the case, for example, in conventional electrical connections to the device ground. In this context, high insulation should mean that, in the deactivated state of the discharge switch, disturbances to the measurement due to parasitic capacitances formed by the discharge switch are avoided as far as possible. In this way, a reduction of the interference caused by triboelectric charging is achieved.

As already mentioned at the outset, the differential voltage measurement system according to the utility model detects bioelectric signals, for example of a human or animal patient. To this end, the differential voltage measurement system has a plurality of measurement lines or active signal paths. The measuring lines or the active signal paths connect, for example, as individual cables, the electrodes which are arranged at the patient to detect the signals to other components of the voltage measuring system, i.e. to the electronics, in particular for evaluating or displaying the detected signals.

The basic function of a differential voltage measurement system is known to the person skilled in the art, and a more detailed explanation is therefore omitted here. The differential voltage measurement system may be designed in particular as an Electrocardiogram (EKG), an electroencephalogram (EEG) or an Electromyogram (EMG).

The differential voltage measurement system according to the utility model has at least one first electrode and a second electrode for measuring a bioelectrical measurement signal. Furthermore, the differential voltage measuring system according to the utility model has a signal measuring circuit according to the utility model. The differential voltage measurement system according to the utility model shares the advantages of the signal measurement circuit according to the utility model.

In addition, particularly advantageous embodiments and refinements of the utility model emerge from the following description, wherein the individual features of the different embodiments or variants can also be combined to form new embodiments or variants.

In one variant of the signal measuring circuit according to the utility model, the discharge switch has a low capacitance of less than 1pF in the deactivated state. Interference or signal loss of the measurement signal can advantageously be avoided by means of the low capacitance. In this way, a measurement signal with lower interference is achieved.

For this purpose, the discharge switch may comprise a reed switch, for example. Such a reed switch may, for example, comprise two ferromagnetic switch reeds which are fused hermetically sealed in a glass vial. The two switch reeds overlap each other. The reed switch can be actuated, for example, by means of a magnet arranged outside the shield of the measuring circuit. If a magnetic field acts on the switch, the two switch springs move towards each other, so that the spring switch closes or an electrical contact is established between the ground line and the input of the amplifier circuit of the signal measuring circuit. The contact areas of the two switching tongues are coated with a very hard metal, so that a high service life can be achieved. Typically, the contact region comprises a very hard and durable material, such as rhodium, ruthenium, tungsten or iridium. The magnetic field generated for the switching process is oriented in the opposite direction, so that the two switching springs attract one another. Conversely, if the force of the magnetic field is less than the spring action of the switch reed, the reed switch opens again.

By using such a reed switch, the capacitance of the controller (Ansteuerung) relative to the sensor line can be kept small, whereby signal losses are likewise avoided, so that signal interference is reduced.

In one variant of the signal measuring circuit according to the utility model, the signal measuring circuit has an electrically shielded housing with a shieldably closed opening. In this embodiment, the already mentioned ground line is to be arranged outside the housing of the signal measuring circuit. More precisely, the ground line should be routed only in the vicinity of the shielded housing, wherein the housing has a shieldably closable opening. In order to ground the sensor line, the opening is then opened and contact is mechanically established between the sensor line and the ground line. During the deactivated state of the ground line, parasitic capacitances of the sensor line due to contact with the ground line are advantageously avoided.

Drawings

The utility model is explained in detail again below with reference to the figures according to embodiments. In the different figures, identical components are provided with the same reference numerals. The drawings are not generally to scale. The figures show:

fig. 1 schematically shows an embodiment of a differential voltage measurement system, comprising a possible positioning of electrical terminals or contacts at a patient,

figure 2 schematically shows a conventional signal measurement circuit of a differential voltage measurement system,

FIG. 3 shows a schematic block diagram of one embodiment of a signal measurement circuit for a differential voltage measurement system according to the present invention.

Detailed Description

In the figures, an EKG measurement system 1 is exemplarily assumed as a differential voltage measurement system 1 in order to measure a bioelectrical signal s (k), here an EKG signal s (k). However, the present invention is not limited thereto.

Fig. 1 shows an exemplary schematic representation of an EKG measurement system 1 according to the utility model, namely an EKG device 17 with its electrical terminals and electrodes 3, 4, 5 connected thereto via a cable K, in order to measure an EKG signal s (K) at a patient P.

For measuring the EKG signal s (k), at least one first electrode 3 and one second electrode 4 are required, which are arranged on the patient P. The electrodes 3, 4 are connected to the EKG device 17 via

terminals

25a, 25b, which are typically plug connectors, by means of a signal measurement cable K. The first electrode 3 and the second electrode 4 together with the signal measuring cable K form part of a signal detection unit, by means of which EKG signals s (K) can be detected.

The third electrode 5 serves as a reference electrode in order to achieve a potential balance between the patient P and the EKG device 17. Conventionally, the third electrode 5 is placed on the right leg of the patient (thus, as mentioned above, the terminal is also commonly referred to as "right leg drive" or "RLD"). However, the third electrode may also be positioned at another location here. Furthermore, via further terminals at the EKG device 17, which are not shown in the figure, a plurality of further contacts for further leads (electrical potential measurement) can also be arranged at the patient P and used for forming suitable signals.

A voltage potential UEKG is formed between the respective electrodes 3, 4, 5₃₄、UEKG₄₅And UEKG₃₅The voltage potential is used to measure the EKG signal s (k).

The directly measured EKG signal s (k) is displayed on the user interface 14 of the EKG device 17.

In the EKG measurement, the patient P is at least capacitively coupled to ground potential E (schematically illustrated in fig. 1 by the coupling at the right leg).

The signal measurement cable K leading from the first electrode 3 and the second electrode 4 to the EKG device 17 is part of the active signal path 6a, 6 b. The signal measurement cable K leading from the electrode 5 to the EKG device 17 corresponds here to a part of the third effective signal path 7N. The third effective signal path 7N transmits an interference signal which has been coupled in via the patient P and the electrodes.

The cable K has a shield S, which is here schematically illustrated as a dashed cylinder surrounding all active signal paths 6a, 6b, 7N. However, the shield does not have to surround all cables K together, but the cables K may also be shielded individually. However, the

terminals

25a, 25b, 25c preferably have poles (Pol) for the shield, respectively, integrated. Then the poles are gathered onto a common shield terminal 25 d. The shielding S is designed here, for example, as a metal film which surrounds the conductors of the respective cable K, said metal film however being insulated from the conductors.

Furthermore, as shown in fig. 1, the EKG device 17 may have an external interface 15, for example to provide terminals for a printer, a storage device and/or even a network. According to one embodiment of the utility model, the EKG device 17 also has signal measurement circuitry 30 (see fig. 3) associated with the

respective terminals

25a, 25 b. The signal measurement circuits 30 are grounded to E via ground switches 31 (see fig. 3), respectively.

Fig. 2 shows an arrangement (Anordnung)20 of individual sensors 3 of an EKG measurement circuit of conventional design. The arrangement comprises a patient P, for example wearing a fabric garment. Above which there may also be a cover 22 transparent to X-rays. The sensor 23 is not in direct electrical contact with the patient, but is electrically insulated from the patient P by the sensor cover 3 a. However, the capacitively coupled input of EKG signals is not impaired by the sensor cover 3 a. The electrodes or sensors 3, the sensor lines 6a running from the sensors 3 to the operational amplifier 27 and the measuring circuit including the operational amplifier 27 are surrounded by a so-called active protective screen 25 and a shield S. The operational amplifier 27 is designed as a so-called follower

I.e. the negative input 27a of operational amplifier 27 is coupled to the output 28 of operational amplifier 27. In this manner, a high virtual input impedance is achieved for the operational amplifier 27 at the positive input 27 b. This means that almost no current flows between the sensor 3 and the active shield or active screen 25 due to the voltage regulation between the output 28 and the positive input 27 b. In addition, the positive input 27b of the operational amplifier 27 is held at a bias voltage by means of a resistor 26 connected to the measurement device ground (also referred to as "measurement ground"). Thereby, the positive input may be placed at a desired measurement potential. The DC component is suppressed in this manner. This is desirable because the sensor 3 should be mainly capacitively coupled and should avoid changing potentials.

The arrangement shown in fig. 2 is illustrated in fig. 3, but now with a signal measurement circuit 30 according to one embodiment of the utility model. The signal measuring circuit 30 substantially corresponds to the embodiment of the signal measuring circuit 20 shown in fig. 2, but has an additional highly insulating switch 31, which provides a connection between the sensor line 6a and the ground potential E or the so-called ideal ground potential. By means of the high-isolation switch, the discharge of the sensor and of the patient's clothing is achieved in the on state. In the state in which the electrical connection to ground potential E is interrupted, switch 31 has a very low capacitance of less than 1pF between sensor line 6a and ground E. In this way, it is prevented that the switch forms a second input which would attenuate the measurement signal in this state.

Finally, it is pointed out again that the device described in detail above is only an embodiment which can be modified in different ways by a person skilled in the art without departing from the scope of the utility model. Thus, the differential voltage measurement system may not only be an EKG device, but also other medical devices for detecting bioelectric signals, such as for example EEG, EMG, etc. Furthermore, the use of the indefinite article "a" or "an" does not exclude that a feature referred to may also be present several times. Likewise, the term "unit" does not exclude that it is made up of a plurality of components, which may also be spatially distributed.

Claims

1. A signal measuring circuit (30) in a differential voltage measuring system (1) for measuring a bioelectric signal by means of a plurality of active signal paths (6a, 6b) each having a sensor electrode (3, 4), the signal measuring circuit having:

-a measurement amplifier circuit (27) for each sensor electrode (3),

-one sensor line (6a) each between the measurement amplifier circuit (27) and the sensor electrode (3, 4),

-a highly insulated discharge switch (31) at the input (27a) of the measurement amplifier circuit (27), which discharge switch electrically connects the sensor line (6a) with a ground line (E).

2. The signal measurement circuit of claim 1,

wherein the discharge switch (31) has a low capacitance of less than 1pF in a deactivated state.

3. The signal measurement circuit of claim 1 or 2,

wherein the discharge switch (31) comprises a reed switch.

4. The signal measurement circuit of claim 3,

wherein the reed switch can be actuated by means of an electromagnet.

5. The signal measurement circuit of claim 4,

wherein the electromagnet is arranged outside a shield (S) of the signal measuring circuit (30).

6. The signal measurement circuit of claim 1 or 2,

wherein the capacitance of the controller of the discharge switch (31) is selected as low as possible with respect to the sensor line (6 a).

7. A signal measurement circuit according to claim 1 or 2, wherein

The signal measuring circuit comprises an electrically shielded housing (23, 24) with a shieldably closed opening,

-the ground line is arranged outside a housing (23, 24) of the signal measurement circuit.

8. A differential voltage measurement system (1) having:

at least one first electrode (3) and a second electrode (4) for measuring a bioelectrical measurement signal,

-a signal measurement circuit (30) according to any of claims 1 to 7.