Measuring equipment

Abstract

A measurement device (1) comprises: a first electrode (11); a second electrode (12); a ground electrode (13) which is disposed between the first electrode (11) and the second electrode (12); a differential circuit (2) which generates a differential voltage between a first voltage that is input from the first electrode (11) and a second voltage that is input from the second electrode (12); a ground terminal (52) which is connected to each of the ground electrode (13), the differential circuit (2), and an output circuit (4); the output circuit (4), which includes an input terminal (41) that receives input of the differential voltage, a reference terminal (42) that receives input of a reference voltage, and a common terminal (43), and which generates a measurement signal on the basis of the differential voltage and the reference voltage and outputs the generated measurement signal; and an impedance element (51) which has a first end (53) that is connected to each of the ground terminal (52) and the common terminal (43) and a second end (54) that is connected to the reference terminal (42).

Description

[Technical Field]

[0001] The present invention relates to a measurement device for measuring a biological signal. [Background technology]

[0002] In recent years, research has been progressing on measurement devices that measure in real time the biological signals of people exercising, such as jogging. Non-Patent Document 1 discloses a measurement circuit that includes a negative electrode attached to the left wrist of a person, a positive electrode attached to the right wrist of the person, an amplifier that outputs the potential difference between the potentials of the positive electrode and the negative electrode, and a ground electrode attached to the ankle to stabilize the potential difference.

[0003] However, in the measurement circuit described in Non-Patent Document 1, the ground electrode is attached to the ankle, making it difficult to measure a person's electrocardiogram signal while the person is performing daily activities. Furthermore, Non-Patent Document 1 does not disclose any method for removing noise signals, including electromyogram signals, body surface potential signals, and internal potential signals, from the measured electrocardiogram signal, making it difficult to accurately detect the electrocardiogram signal. While a method for removing noise signals mixed into the measured electrocardiogram signal by signal processing could be considered, this would require a separate signal processing circuit to be provided in the electrocardiograph, which would increase the size and cost of the electrocardiograph. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Nikkei Crosstech, Measure your heart rate just by wearing it. What is the capability of that device? [online], February 5, 2016, [Retrieved April 2, 2021], Internet,<URL:https: / / xtech.nikkei.com / dm / atcl / column / 15 / 110200016 / 122100017 / ?P=4> Summary of the Invention

[0005] The present invention has been made to solve the above problems, and has an object to provide a measurement device that can accurately remove noise signals while having a simple configuration.

[0006] A measuring device in one aspect of the present invention is a measuring device that measures a biological signal, and includes: a first electrode that is placed in a measurement area of ​​the body corresponding to the biological signal to be measured; a second electrode that is placed in the measurement area; a ground electrode that is placed between the first electrode and the second electrode in the measurement area; a differential circuit that generates a differential voltage between a first voltage input from the first electrode and a second voltage input from the second electrode; an output circuit that includes an input terminal to which the differential voltage is input, a reference terminal to which a reference voltage is input, and a common terminal, and that generates a measurement signal based on the differential voltage and the reference voltage and outputs the generated measurement signal; ground terminals connected to the ground electrode, the differential circuit, and the output circuit, respectively; and an impedance element whose first end is connected to the ground terminal and the common terminal, respectively, and whose second end is connected to the reference terminal.

[0007] According to the present invention, noise signals can be removed with high accuracy despite the simple configuration. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a circuit diagram illustrating an example of a configuration of a measurement device according to an embodiment of the present disclosure. [Figure 2] 10A and 10B are diagrams showing examples of attachment of a first electrode, a second electrode, and a ground electrode to a human being. [Figure 3] FIG. 2 is a diagram showing a first example of a measurement area. [Figure 4] FIG. 10 is a diagram showing a second example of a measurement region. [Figure 5] 10A and 10B are diagrams illustrating an example of mounting a first terminal, a second terminal, and a ground terminal. [Figure 6] 10 is a graph showing experimental results when electrocardiogram signals were measured on a subject in a stationary state using a measurement device of a comparative example. [Figure 7]10 is a graph showing experimental results when electrocardiogram signals are measured on a subject in a stationary state using the measurement device of the present embodiment. [Figure 8] 10 is a graph showing experimental results when electrocardiogram signals were measured on a subject in a jogging state using a measuring device of a comparative example. [Figure 9] 10 is a graph showing experimental results when electrocardiogram signals are measured using the measurement device of the present embodiment on a subject in a jogging state. [Figure 10] 10 is a graph showing experimental results when electrocardiogram signals of a running subject are measured using a measurement device in which the impedance of the impedance element is 0Ω. [Figure 11] 10 is a graph showing experimental results when electrocardiogram signals of a running subject are measured using a measurement device in which the impedance of the impedance element is 1.0 MΩ. [Figure 12] 10 is a graph showing experimental results when electrocardiogram signals of a running subject are measured using a measurement device in which the impedance of the impedance element is 3.9 MΩ. [Figure 13] 10 is a graph showing experimental results when an electrocardiogram signal of a running subject is measured using a measurement device in which the impedance of an impedance element is ∞Ω. [Figure 14] 10 is a graph showing experimental results when electrocardiogram signals of a subject in an arm swinging state are measured using a measuring device in which the impedance of the impedance element is 0Ω. [Figure 15] 10 is a graph showing experimental results when electrocardiogram signals of a subject in a swinging arm state are measured using a measuring device with an impedance element having an impedance of 1.0 Ω. [Figure 16] 10 is a graph showing experimental results when electrocardiogram signals of a subject in a swinging arm state are measured using a measuring device with an impedance element having an impedance of 3.9 MΩ. [Figure 17] 10 is a graph showing experimental results when an electrocardiogram signal of a subject in a swinging arm state is measured using a measurement device in which the impedance of an impedance element is ∞Ω. [Figure 18]FIG. 10 is a diagram showing an example of how the first electrode, the second electrode, and the ground electrode are attached when the measurement area is the back. [Figure 19] FIG. 2 is a diagram showing a first electrode, a second electrode, and a ground electrode attached to a bathtub. [Figure 20] FIG. 1 shows a person bathing in a bathtub. [Figure 21] FIG. 1 is a diagram showing an electrocardiogram signal of a person taking a bath. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the following embodiment is an example of a specific embodiment of the present invention and is not intended to limit the technical scope of the present invention.

[0010] FIG. 1 is a circuit diagram showing an example of the configuration of a measurement device 1 according to an embodiment of the present disclosure. The measurement device 1 is a device that measures a biological signal. The biological signal may be, for example, a biological signal from a human body. Hereinafter, the biological signal to be measured will be referred to as a "target biological signal." The target biological signal will be described as an electrocardiogram signal. However, this is just an example, and the target biological signal may also be an electromyogram signal or an electroencephalogram signal.

[0011] The measurement device 1 includes a first electrode 11, a second electrode 12, a ground electrode 13, a differential circuit 2, an amplifier circuit 3, an output circuit 4, and an elimination circuit 5. The first electrode 11 is placed in a measurement region of the body according to a target biosignal. In this case, since the target biosignal is an electrocardiogram signal, the measurement region is a region near the heart, for example, a region on the upper torso. The second electrode 12 is placed in the measurement region. The ground electrode 13 is placed between the first electrode 11 and the second electrode 12 in the measurement region.

[0012] The differential circuit 2 generates a differential voltage between a first voltage input from the first electrode 11 and a second voltage input from the second electrode 12. The differential circuit 2 includes an input terminal 21, an input terminal 22, a ground terminal 23, and an output terminal 24. The input terminal 21 is connected to the first electrode 11 and receives the first voltage. The input terminal 22 is connected to the second electrode 12 and receives the second voltage. The ground terminal 23 is connected to the ground electrode 13 and the ground terminal 52. The output terminal 24 is connected to the input terminal 31 of the amplifier circuit 3. The differential circuit 2 may have, for example, a high-pass filter function that passes signals above a predetermined cutoff frequency and / or a function that amplifies the input signal. For example, the differential circuit 2 may be a differential amplifier circuit or an instrumentation amplifier circuit.

[0013] The amplifier circuit 3 amplifies the difference voltage and inputs the amplified difference voltage to the output circuit 4. The amplifier circuit 3 includes an input terminal 31 and an output terminal 32. The output terminal 32 is connected to an input terminal 41 of the output circuit 4. The amplifier circuit 3 is configured with a known amplifier circuit including, for example, an operational amplifier. The amplifier circuit 3 may have a low-pass filter function that passes voltages below a predetermined cutoff frequency and / or a function that inverts and outputs the voltage input to the input terminal 31. The amplifier circuit 3 amplifies the difference signal with a predetermined gain that is suitable for, for example, an analog-to-digital converter 44 to convert the difference signal into an analog-to-digital signal.

[0014] The ground terminal 52 is connected to the ground electrode 13, the differential circuit 2, and the amplifier circuit 3, and sets a reference potential for the ground electrode 13, the differential circuit 2, and the amplifier circuit 3. The reference potential is, for example, 0V.

[0015] The output circuit 4 includes an input terminal 41, a reference terminal 42, a common terminal 43, an analog-to-digital converter 44, and a wireless communication circuit 45. The input terminal 41 is connected to the output terminal 32 and receives the differential voltage. The reference terminal 42 receives the reference voltage. The common terminal 43 is a ground terminal of the output circuit 4 and sets the reference potential of the output circuit 4. The output circuit 4 generates a measurement signal based on the differential voltage and the reference voltage, and outputs the generated measurement signal.

[0016] The analog-digital converter 44 is, for example, a flash analog-digital converter. However, this is just one example, and the analog-digital converter 44 may be configured as a pipeline, successive approximation, or ΔΣ analog-digital converter. The analog-digital converter 44 includes a ladder resistor unit 46, a comparator unit 47, and an encoder 48. The ladder resistor unit 46 has a first end connected to the reference terminal 42 and a second end connected to the common terminal 43. The ladder resistor unit 46 divides a reference voltage input to the reference terminal 42 into 2n-1 voltages (n is an integer equal to or greater than 2). The comparator unit 47 has a first end connected to the input terminal 41. The comparator unit 47 simultaneously compares each of the 2n-1 divided reference voltages with the difference voltage. The encoder 48 generates a measurement signal by converting the comparison result into a digital signal.

[0017] The wireless communication circuit 45 converts the measurement signal generated by the analog-to-digital converter 44 into a wireless signal and outputs the converted wireless signal to an external device. The wireless communication circuit 45 is configured with a circuit that performs close proximity wireless communication such as Bluetooth Low Energy, for example.

[0018] This allows the measurement signal to be output to an external device without restricting human movement. The external device is, for example, a mobile device such as a smartphone. This mobile device has, for example, a healthcare app installed. The healthcare app calculates the user's heart rate in real time based on the received measurement signal and presents it to the user. This allows the user to check their own heart rate in real time while performing some activity, such as running.

[0019] The elimination circuit 5 is a circuit that eliminates noise signals mixed in with the measurement signal. The elimination circuit 5 includes an impedance element 51.

[0020] The impedance element 51 includes a first end 53 and a second end 54. The first end 53 is connected to the ground terminal 52 and the common terminal 43, respectively. The second end 54 is connected to the reference terminal 42.

[0021] The impedance element 51 is a resistor, a capacitor, an inductor, a diode, or a transistor. The impedance of the impedance element 51 has a value equal to or greater than the bioimpedance of a human being, and is preferably 1 to 10 times, and more preferably 3 to 5 times, the bioimpedance of a human being. The bioimpedance of a human being is, for example, 1 MΩ.

[0022] When the impedance of the impedance element 51 is 0Ω, the ground terminal 52 and the reference terminal 42 are short-circuited.

[0023] Furthermore, when the impedance of impedance element 51 is ∞Ω, ground terminal 52 and reference terminal 42 are open.

[0024] In these configurations, noise signals cannot be removed as will be described later, so in this embodiment, the impedance of impedance element 51 is set within the range greater than 0Ω and smaller than ∞Ω.

[0025] FIG. 2 is a diagram showing an example of attachment of the first electrode 11, the second electrode 12, and the ground electrode 13 to a human 100. When measuring an electrocardiogram signal, the measurement region 10 is set, for example, on the torso of the human 100. In the example of FIG. 2, the measurement region 10 is set to an area that includes the heart, which is approximately one-quarter of the upper part of the torso. Hereinafter, "left" refers to the left direction when the human 100 is viewed from the front, and "right" refers to the right direction when the human 100 is viewed from the front. Furthermore, "left" and "right" are collectively referred to as the left-right direction. Furthermore, the head side of the human 100 is referred to as the upper side, and the foot side of the human 100 is referred to as the lower side. Furthermore, "upper" and "lower" are collectively referred to as the up-down direction.

[0026] In the measurement area 10, the first electrode 11 is disposed on the left, and the second electrode 12 is disposed on the right. The ground electrode 13 is disposed between the first electrode 11 and the second electrode 12 in the measurement area 10. Here, "between the first electrode 11 and the second electrode 12" means that, as shown in FIG. 3 , a projection point P1 of the ground electrode 13 on a line L1 connecting the first electrode 11 and the second electrode 12 is located between the first electrode 11 and the second electrode 12.

[0027] FIG. 3 is a diagram showing a first example of the measurement area 10. In the first example, the measurement area 10 is rectangular. In the example of FIG. 3, the first electrode 11 is disposed at the left end of the measurement area 10, and the second electrode 12 is disposed at the right end of the measurement area 10. The ground electrode 13 is disposed above a line L1 connecting the first electrode 11 and the second electrode 12 in the measurement area 10. The ground electrode 13 may also be disposed below the line L1. The ground electrode 13 may also be disposed at the upper end or the lower end of the measurement area 10. The first electrode 11 may be disposed at a location other than the left end within the measurement area 10, and the second electrode 12 may be disposed at a location other than the right end within the measurement area 10.

[0028] 4 is a diagram showing a second example of the measurement area 10. In the second example, the measurement area 10 is a parallelogram. In the second example, too, the projection point P1 of the ground electrode 13 onto the line L1 is located on the line segment connecting the first electrode 11 and the second electrode 12, and the ground electrode 13 is disposed between the first electrode 11 and the second electrode 12. In addition, the first electrode 11 is disposed above the second electrode 12.

[0029] FIG. 5 is a diagram showing an example of the implementation of the first electrode 11, the second electrode 12, and the ground electrode 13. The first electrode 11, the second electrode 12, and the ground electrode 13 are attached to the chest of the underwear 101. Here, the first electrode 11, the second electrode 12, and the ground electrode 13 are arranged in a substantially straight line. In this example, the ground electrode 13 is also arranged between the first electrode 11 and the second electrode 12. By attaching the first electrode 11, the second electrode 12, and the ground electrode 13 to the underwear 101 in this way, the person 100 can have the first electrode 11, the second electrode 12, and the ground electrode 13 arranged on the chest simply by wearing the underwear 101.

[0030] Next, the operation of the measurement device 1 shown in FIG. 1 will be described. The first electrode 11 inputs a first voltage obtained by measuring the human 100 to the input terminal 21 of the differential circuit 2. At the same time, the second electrode 12 inputs a second voltage obtained by measuring the human 100 to the input terminal 22 of the differential circuit 2. The differential circuit 2 generates a differential voltage from the input first and second voltages and inputs the differential voltage to the amplifier circuit 3. The amplifier circuit 3 amplifies the input differential voltage and inputs the amplified differential voltage to the analog-to-digital converter 44. The analog-to-digital converter 44 generates a measurement signal by analog-to-digital conversion of the input differential voltage and inputs the measurement signal to the wireless communication circuit 45. The wireless communication circuit 45 converts the measurement signal into a wireless signal and transmits it to an external device.

[0031] Next, the function of the elimination circuit 5 will be described. First, case C1, in which the impedance of impedance element 51 is 0Ω, will be described. A noise signal flowing in from ground electrode 13 is discharged to ground terminal 52. However, in case C1, ground terminal 52 and reference terminal 42 are short-circuited, so this noise signal is input to reference terminal 42 without being reduced. As a result, the potential of reference terminal 42 dynamically fluctuates in conjunction with the noise signal, and analog-to-digital converter 44 is unable to accurately convert the difference signal into a digital signal. If the target biological signal is an electrocardiogram signal, the noise signals are electromyogram signals, body surface potential signals, and internal body potential signals.

[0032] Next, we will explain case C2, where the impedance of impedance element 51 is ∞Ω. In case C2, ground terminal 52 and reference terminal 42 are open, so reference terminal 42 is floating from ground terminal 52. In this case, ground terminal 52 and ground electrode 13 do not function, and analog-to-digital converter 44 cannot accurately convert the difference signal into a digital signal.

[0033] Therefore, in this embodiment, the impedance of impedance element 51 is set within a range greater than 0Ω and less than ∞Ω. Therefore, the noise signal input to reference terminal 42 described in Case C1 is consumed by impedance element 51. This stabilizes the potential of reference terminal 42, allowing analog-to-digital converter 44 to accurately convert the differential voltage. Furthermore, it has been confirmed that when measurement device 1 has ground electrode 13 disposed between first electrode 11 and second electrode 12, the accuracy of the biosignal of the measurement target is improved compared to when the ground electrode is not disposed between the first electrode and the second electrode. Therefore, the biosignal of the measurement target can be measured with high accuracy.

[0034] In particular, if the impedance of the impedance element 51 is set to a value at least comparable to the bioimpedance, the impedance element 51 can consume more noise signals, and the noise signals are removed with higher accuracy.

[0035] Furthermore, if the impedance of the impedance element 51 is set to 3 to 10 times, preferably 3 to 5 times, the bioimpedance, the impedance element 51 can consume even more noise signals, and the noise signals can be removed with even greater accuracy.

[0036] The following describes the results of an experiment conducted to confirm the effects of the measurement device 1. FIG. 6 is a graph showing the results of an experiment in which electrocardiogram signals were measured on a subject in a stationary state using a measurement device of a comparative example. FIG. 7 is a graph showing the results of an experiment in which electrocardiogram signals were measured on a subject in a stationary state using the measurement device 1. The measurement device of the comparative example has a configuration in which the ground electrode 13 is omitted from the measurement device 1. This is also true for the graphs of FIGS. 8 and 9.

[0037] In Figures 6 and 7, graph G1 shows the time progression of the electrocardiogram signal, with the vertical axis representing amplitude and the horizontal axis representing time. In Figures 6 and 7, graph G2 shows the frequency spectrum of the electrocardiogram signal, with the vertical axis representing amplitude and the horizontal axis representing frequency. In Figures 6 and 7, column R1 shows the heart rate per minute obtained from the electrocardiogram signal. The same applies to the graphs in Figures 8 and 9.

[0038] The measurement device of the comparative example measured only the first and second harmonics of the electrocardiogram signal, as shown in graph G2 of Fig. 6. In contrast, the measurement device 1 measured the first through fourth harmonics of the electrocardiogram signal, as shown in graph G2 of Fig. 7. Therefore, it was confirmed that the measurement device 1 can measure electrocardiogram signals with higher accuracy than the measurement device of the comparative example.

[0039] Fig. 8 is a graph showing the experimental results when electrocardiogram signals of a subject in a jogging state were measured using a measurement device of a comparative example. Fig. 9 is a graph showing the experimental results when electrocardiogram signals of a subject in a jogging state were measured using measurement device 1.

[0040] The measurement device of the comparative example measured only electrocardiogram signals up to the first and second harmonics, as shown in graph G2 of Fig. 8. In contrast, the measurement device 1 measured electrocardiogram signals from the first to third harmonics, as shown in graph G2 of Fig. 9. This confirmed that the measurement device 1 can measure electrocardiogram signals more accurately than the measurement device of the comparative example. Furthermore, when comparing a stationary state with a jogging state, it was confirmed that the stationary state measured electrocardiogram signals more accurately.

[0041] Next, the results of an experiment conducted to confirm the influence of the impedance value of the impedance element 51 on measurement accuracy will be described.

[0042] FIG. 10 is a graph showing experimental results when the electrocardiogram signal of a running subject was measured using a measurement device 1 in which the impedance of the impedance element 51 was 0Ω. In FIG. 10, graph G1 shows the time progression of the electrocardiogram signal, with the vertical axis representing amplitude and the horizontal axis representing time. Graph G2 shows the frequency spectrum of the electrocardiogram signal, with the vertical axis representing amplitude and the horizontal axis representing frequency. Column R1 shows the heart rate per minute obtained from the electrocardiogram signal, column R2 shows the heart rate per minute obtained from the first harmonic of the electrocardiogram signal, column R3 shows the heart rate per minute obtained from the second harmonic of the electrocardiogram signal, and column R4 shows the heart rate per minute obtained from the third harmonic of the electrocardiogram signal. The same applies to the graphs in FIGS. 11 to 17.

[0043] Fig. 11 is a graph showing experimental results when the electrocardiogram signal of a running subject was measured using a measurement device 1 with an impedance element 51 having an impedance of 1.0 MΩ. Fig. 12 is a graph showing experimental results when the electrocardiogram signal of a running subject was measured using a measurement device 1 with an impedance element 51 having an impedance of 3.9 MΩ. Fig. 13 is a graph showing experimental results when the electrocardiogram signal of a running subject was measured using a measurement device 1 with an impedance element 51 having an impedance of ∞ Ω.

[0044] Comparing Figures 10 to 13, the heart rate per minute of the third harmonic was "71" when the impedance was 0 MΩ, "89" when the impedance was 1 MΩ, "99" when the impedance was 3.9 MΩ, and "76" when the impedance was ∞ Ω. Therefore, the amplitude of the third harmonic was greatest when the impedance was 3.9 MΩ, followed by when the impedance was 1 MΩ, then when the impedance was ∞ Ω, and then when the impedance was 0 MΩ. Since the subject's bioimpedance was approximately 1 MΩ, it was confirmed that the measurement accuracy of the electrocardiogram signal was improved by setting the impedance to approximately 3.9 times the bioimpedance. Furthermore, it was confirmed that the heart rate per minute of the third harmonic decreased when the impedance was significantly smaller than the bioimpedance or when the impedance was significantly larger than the bioimpedance, and that the measurement accuracy of the electrocardiogram signal decreased when the impedance was set to ∞ Ω.

[0045] Fig. 14 is a graph showing experimental results when electrocardiographic signals of a subject in a swinging arm state were measured using a measurement device 1 with an impedance element 51 having an impedance of 0Ω. Fig. 15 is a graph showing experimental results when electrocardiographic signals of a subject in a swinging arm state were measured using a measurement device 1 with an impedance element 51 having an impedance of 1.0Ω. Fig. 16 is a graph showing experimental results when electrocardiographic signals of a subject in a swinging arm state were measured using a measurement device 1 with an impedance element 51 having an impedance of 3.9 MΩ. Fig. 17 is a graph showing experimental results when electrocardiographic signals of a subject in a swinging arm state were measured using a measurement device 1 with an impedance element 51 having an impedance of ∞Ω.

[0046] Comparing Figures 14 to 17, the heart rate per minute of the third harmonic was "93" when the impedance was 0Ω, "81" when the impedance was 1 MΩ, "97" when the impedance was 3.9 MΩ, and "94" when the impedance was ∞Ω. Therefore, the heart rate per minute of the third harmonic was greatest when the impedance was 3.9 MΩ, followed by when the impedance was ∞ MΩ, then when the impedance was 0 MΩ, and then when the impedance was 1 MΩ. The heart rate per minute of the first harmonic was greater when the impedance was 3.9 MΩ than when it was ∞ Ω. This confirmed that the accuracy of the electrocardiogram signal was good when the impedance was 3.9 MΩ.

[0047] The present invention can employ the following modifications.

[0048] (1) When the measurement signal is an electroencephalogram signal, the measurement region 10 may be set to the head of the person 100.

[0049] (2) When the measurement signal is an electromyographic signal, the measurement region 10 may be set to a region including the muscle part to be measured. For example, when measuring the electromyographic signal of the calf or thigh, the measurement region 10 is set to the calf or thigh. When measuring the electromyographic signal of the arm, the measurement region 10 is set to the arm.

[0050] (3) The measurement area 10 may be the chest or back of the torso of the human 100. FIG. 18 is a diagram showing an example of attachment of the first electrode 11, the second electrode 12, and the ground electrode 13 when the measurement area 10 is the back. In FIG. 18, when viewing the human 100 from behind, the right direction is called the right side and the left direction is called the left side. In the example of FIG. 18, the measurement area 10 is set in the center of the back, but this is just one example. The measurement area 10 may be located in a location other than the center, such as the upper or lower part of the back. In the measurement area 10, the first electrode 11 is located on the left, and the second electrode 12 is located on the right. In the measurement area 10, the first electrode 11 is located on the left, and the second electrode 12 is located on the right. The ground electrode 13 is located between the first electrode 11 and the second electrode 12. "Between the first electrode 11 and the second electrode 12" is as described in FIG. 3.

[0051] In this way, when the first electrode 11, the second electrode 12, and the ground electrode 13 are placed on the back, an electrocardiogram signal can be measured, which makes it easy to count the heart rate and respiratory rate. Furthermore, it becomes difficult for a person 100, such as a person with dementia or requiring care, to remove the first electrode 11, the second electrode 12, and the ground electrode 13 from their back, making it possible to measure the heart rate continuously. Furthermore, a caregiver can easily attach the first electrode 11, the second electrode 12, and the ground electrode 13 to the person 100 who requires care.

[0052] (4) The first electrode 11, the second electrode 12, and the ground electrode 13 do not have to be directly attached to the human 100.

[0053] 19 is a diagram showing the first electrode 11, the second electrode 12, and the ground electrode 13 attached to the bathtub 200. The bathtub 200 includes an inner surface 201. The inner surface 201 is the inner surface located on the head side of the person 100 when the person 100 is lying down in the bathtub 200. The first electrode 11, the second electrode 12, and the ground electrode 13 are attached side by side in the left-right direction (horizontal direction) on the inner surface 201. In detail, the ground electrode 13 is attached between the first electrode 11 and the second electrode 12.

[0054] 20 is a diagram showing a person 100 bathing in a bathtub 200. When the person 100 lies down in the bathtub 200 with his / her back in contact with the inner surface 201, the back of the person 100 comes into contact with the first electrode 11, the second electrode 12, and the ground electrode 13. As a result, the measurement device 1 can measure the electrocardiogram waveform of the person 100 in a relaxed state after bathing.

[0055] In this embodiment, "the first electrode 11, the second electrode 12, and the ground electrode 13 are arranged in the measurement area of ​​the body" not only refers to a case where the first electrode 11, the second electrode 12, and the ground electrode 13 are directly attached to the human 100, but also refers to a case where the first electrode 11, the second electrode 12, and the ground electrode 13 come into contact with the human 100 as a result of the human 100 abutting his or her body against an object to which the first electrode 11, the second electrode 12, and the ground electrode 13 are attached.

[0056] Fig. 21 is a diagram showing the electrocardiogram signal of person 100 while bathing. In Fig. 21, the vertical axis represents voltage and the horizontal axis represents time. As shown in Fig. 21, it was confirmed that by arranging first electrode 11, second electrode 12, and ground electrode 13 in bathtub 200, it is possible to measure an electrocardiogram signal that clearly shows P waves, R waves, and T waves.

[0057] (Summary of the embodiment) The technical features of the embodiment are summarized as follows.

[0058] A measuring device in one aspect of the present invention is a measuring device that measures a biological signal, and includes: a first electrode that is placed in a measurement area of ​​the body corresponding to the biological signal to be measured; a second electrode that is placed in the measurement area; a ground electrode that is placed between the first electrode and the second electrode in the measurement area; a differential circuit that generates a differential voltage between a first voltage input from the first electrode and a second voltage input from the second electrode; an output circuit that includes an input terminal to which the differential voltage is input, a reference terminal to which a reference voltage is input, and a common terminal, and that generates a measurement signal based on the differential voltage and the reference voltage and outputs the generated measurement signal; ground terminals connected to the ground electrode, the differential circuit, and the output circuit, respectively; and an impedance element whose first end is connected to the ground terminal and the common terminal, respectively, and whose second end is connected to the reference terminal.

[0059] According to this configuration, the ground electrode disposed between the first and second electrodes functions to shunt noise signals, including biosignals not being measured, to the ground terminal. Furthermore, according to this configuration, an impedance element is provided, the first end of which is connected to the ground terminal and the common terminal, and the second end of which is connected to the reference terminal. Therefore, even if a noise signal shunted to the ground terminal flows back toward the reference terminal, the backflowing noise signal is consumed by the impedance element. This prevents noise signals from being mixed into the reference terminal, allowing for accurate removal of the noise signal. Furthermore, it has been confirmed that when the ground electrode is disposed between the first and second electrodes in a measurement region of the body corresponding to the biosignal being measured, the accuracy of the biosignal being measured is improved compared to when the ground electrode is not disposed between the first and second electrodes. Therefore, the biosignal being measured can be measured accurately.

[0060] Furthermore, since noise signals are removed by such a configuration, there is no need to provide a separate signal processing circuit, which can reduce the size and cost of the device.

[0061] In the above-described measuring device, the impedance element may have an impedance equal to or greater than the bioimpedance of a living body.

[0062] According to this configuration, since the impedance element has an impedance equal to or greater than the bioimpedance, noise signals can be removed promptly immediately after the start of measurement.

[0063] In the measuring device, the impedance of the impedance element may be 3 to 10 times the bioimpedance.

[0064] According to this configuration, the impedance element has an impedance three to ten times higher than the bioimpedance, so that noise signals can be removed quickly immediately after the start of measurement.

[0065] In the above measurement device, the biological signal to be measured may be an electrocardiogram signal, an electroencephalogram signal, or an electromyogram signal.

[0066] According to this configuration, electrocardiogram signals, electroencephalogram signals, or electromyogram signals can be measured with high accuracy.

[0067] In the above-described measuring device, the impedance element may be a resistor, a capacitor, an inductor, a diode, or a transistor.

[0068] According to this configuration, the impedance element is a resistor, a capacitor, an inductor, a diode, or a transistor, so that the impedance element can be configured simply and at low cost using existing circuit elements.

[0069] In the above-described measuring device, the output circuit may include an analog-to-digital converter that converts the differential voltage into a digital signal based on the differential voltage and the reference voltage, and outputs the converted digital signal as the measurement signal.

[0070] According to this configuration, the differential voltage is converted into a digital signal to generate the measurement signal, so that the measurement signal can be output to an external device with high accuracy.

[0071] In the above-described measuring device, the output circuit may include a wireless communication circuit that converts the measurement signal into a wireless signal and outputs the wireless signal to an external device.

[0072] According to this configuration, the measurement signal is converted into a wireless signal and output to the external device, so that the measurement signal can be output to the external device without restricting the movement of the living body.

[0073] The measuring device may further include an amplifier circuit that amplifies the differential voltage and inputs the amplified differential voltage to the output circuit.

[0074] According to this configuration, the differential voltage from the differential circuit is amplified, so that the amplitude of the differential voltage can be adjusted to an amplitude suitable for the output circuit to generate a measurement signal.

[0075] In the above-described measurement device, the measurement area may be the back.

[0076] With this configuration, an electrocardiogram signal can be obtained that allows the heart rate and respiratory rate to be easily counted.

[0077] In the above-described measuring device, the first electrode, the second electrode, and the ground electrode may be attached to an inner surface of a bathtub.

[0078] With this configuration, it is possible to measure the measurement signal of a person who is in a relaxed state while taking a bath.

Claims

1. A measurement device for measuring a biological signal, a first electrode to be placed in a measurement region of the body corresponding to a biological signal to be measured; a second electrode disposed in the measurement region; a ground electrode disposed between the first electrode and the second electrode in the measurement region; a differential circuit that generates a differential voltage between a first voltage input from the first electrode and a second voltage input from the second electrode; an output circuit including an input terminal to which the differential voltage is input, a reference terminal to which a reference voltage is input, and a common terminal, the output circuit generating a measurement signal based on the differential voltage and the reference voltage, and outputting the generated measurement signal; ground terminals connected to the ground electrode, the differential circuit, and the output circuit; an impedance element having a first end connected to each of the ground terminal and the common terminal and a second end connected to the reference terminal; Measuring equipment.

2. The impedance element has an impedance equal to or greater than the bioimpedance of a living body. The measuring device according to claim 1.

3. The impedance of the impedance element is 3 to 10 times the bioimpedance. The measuring device according to claim 2.

4. The biological signal to be measured is an electrocardiogram signal, an electroencephalogram signal, or an electromyogram signal. The measuring device according to claim 1.

5. The impedance element is a resistor, a capacitor, an inductor, a diode, or a transistor. The measuring device according to claim 1.

6. the output circuit includes an analog-to-digital converter that converts the differential voltage into a digital signal based on the differential voltage and the reference voltage, and outputs the converted digital signal as the measurement signal. The measuring device according to claim 1.

7. the output circuit includes a wireless communication circuit that converts the measurement signal into a wireless signal and outputs the wireless signal to an external device; The measuring device according to claim 1.

8. further comprising an amplifier circuit that amplifies the differential voltage and inputs the amplified differential voltage to the output circuit; The measuring device according to claim 1.

9. The measurement area is the back. The measuring device according to claim 1.

10. The first electrode, the second electrode, and the ground electrode are attached to an inner surface of a bathtub. The measuring device according to any one of claims 1 to 9.

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