JP2012213458A - Bio-impedance meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bio-impedance meter for appropriately detecting an abnormal condition caused by the influence of a contact impedance.SOLUTION: The bio-impedance meter includes a constant electric current portion 20 for applying a predetermined alternating current within the range of maximum supply voltage to a living body 900 through electrodes 1 and 2, and a voltage measuring portion 21 for measuring a fall voltage caused by the current flowing in the living body, through electrodes 3 and 4. The voltage measuring portion 21 includes a differential amplifier circuit 22 for inputting and differentially amplifying the fall voltage within the range of maximum input voltage. When the supply voltage to the electrode 1 or electrode 2 from the constant electric current portion 20, exceeds the range of allowable supply voltage set within the range of maximum supply voltage, or when the input voltage to the differential amplifier circuit 33 from a third electrode 3 or fourth electrode 4, exceeds the range of allowable input voltage set within the range of maximum input voltage, an error detecting portion 40 determines contact error between the living body 900 and the electrode 1, 2, 3, or 4.

Description

  The present invention relates to a bioimpedance measuring apparatus, and more particularly to an apparatus for measuring the impedance of a living body by a four terminal method.

  As a general bioimpedance measuring apparatus of this type, as shown in FIG. 11A, on the mounting plate 10, the first electrode 1 to be brought into contact with the toe side 901 of the left foot and the toe side 902 of the right foot There is one provided with the second electrode 2 to be contacted, the third electrode 3 to be in contact with the left foot heel 903, and the fourth electrode 4 to be in contact with the right foot heel 904. With the left and right soles of the living body 900 placed on the mounting plate 10, the constant current source 20 causes the living body 900 to pass through the first electrode 1 and the second electrode 2 as shown in FIG. A predetermined energization current (alternating current) I is supplied. Then, a voltage drop V caused by the flowing of the energization current I through the living body 900 is measured by the voltage measurement unit 21 via the third electrode 3 and the fourth electrode 4 (four-terminal method). The body composition value calculated based on the impedance obtained by converting the voltage drop V into a numerical value (dividing by the energizing current I) is displayed on the display unit 22 shown in FIG. The voltage measuring unit 21 amplifies the difference between the voltage V1 from the third electrode 3 and the voltage V2 from the fourth electrode 4 and outputs a signal Vo1 representing the amplification result; A rectifier circuit 23 that rectifies the output signal Vo1 of the differential amplifier circuit 22, a smoothing circuit 24 that smoothes the output of the rectifier circuit 23, and an output of the smoothing circuit 24 that is A / D converted to a digital signal. And an A / D conversion circuit 25 for outputting as Vo2. The control unit 30 calculates impedance and body composition values and creates a signal to be displayed on the display unit 22.

  Here, how to put the foot on the electrode, that is, the change of the position where the foot is placed, the floating state of the foot, and the like are determined by the right and left soles 901, 902, 903, 904 and the electrodes 1, 2, 3, 4 Contact impedances FILR, FIRR, FVLR, and FVRR may be increased, which causes an error in impedance measurement.

  In a conventional bioimpedance measuring device, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 8-154911), when the impedance measurement result is not within a specified range, the time required for the measurement is set to a specified time. It is known to display an error message when exceeded.

JP-A-8-154911

  However, the conventional bioelectrical impedance measuring apparatus has a problem that an error can be detected only when the impedance measurement result is extremely out of the specified range, that is, when the influence of the contact impedance is extremely large. For this reason, even if the contact impedance is large (abnormal), if the measurement data is stabilized during the specified time, an erroneous measurement result is displayed.

  Recently, in order to improve the design, the electrodes 1, 2, 3, and 4 tend to be miniaturized, and instead of SUS (stainless steel) as an electrode material, ITO (tin-added indium oxide) is used. Transparent electrodes such as are being adopted. For this reason, the factors that increase the contact impedance are increasing, and it is an urgent need to appropriately detect abnormality due to the influence of the contact impedance.

  Accordingly, an object of the present invention is to provide a bioimpedance measuring apparatus that can appropriately detect an abnormality caused by the influence of contact impedance.

In order to solve the above problems, the bioimpedance measuring device of the present invention is:
A first electrode and a second electrode to be brought into contact with the living body, respectively, and a third electrode and a fourth electrode to be brought into contact with portions corresponding to the first electrode and the second electrode in the living body,
A constant current section for supplying a predetermined alternating current to the living body within a maximum supply voltage range via the first electrode and the second electrode;
A voltage measurement unit including a differential amplifier circuit that differentially amplifies a voltage drop caused by the alternating current flowing through the living body through the third electrode and the fourth electrode within a maximum input voltage range; ,
When the supply voltage from the constant current section to the first electrode or the second electrode exceeds the allowable supply voltage range set within the maximum supply voltage range, or the difference from the third electrode or the fourth electrode When the input voltage to the dynamic amplifier circuit exceeds the allowable input voltage range set within the maximum input voltage range, the living body and the first electrode, the second electrode, the third electrode, and the fourth electrode An error detection unit that determines that there is a contact error is provided.

  In the bioimpedance measuring apparatus according to the present invention, the constant current section causes a predetermined alternating current to flow through the living body via the first electrode and the second electrode. The voltage measurement unit measures a voltage drop caused by the alternating current flowing through the living body via the third electrode and the fourth electrode. Specifically, a differential amplifier circuit included in the voltage measuring unit inputs the voltage drop within the maximum input voltage range and performs differential amplification. The voltage drop is measured by rectifying, smoothing, and A / D converting the output of the differential amplifier circuit. The impedance of the living body is obtained by converting the voltage drop measured by the voltage measuring unit into a numerical value (dividing by the energizing current). On the other hand, when the supply voltage from the constant current unit to the first electrode or the second electrode exceeds the allowable supply voltage range set within the maximum supply voltage range, or the error detection unit, When the input voltage from the fourth electrode to the differential amplifier circuit exceeds the allowable input voltage range set within the maximum input voltage range, the living body and the first electrode, the second electrode, the third electrode, It is determined that there is a contact error with the fourth electrode. The determination result related to the contact error is different from the measurement result related to the impedance, and the allowable supply voltage range related to the constant current portion at a stage before the supply voltage from the constant current portion to the first electrode or the second electrode is saturated. Or in real time based on whether or not the differential amplifier circuit allowable input voltage range is exceeded. Therefore, according to this bioimpedance measuring apparatus, it is possible to appropriately detect abnormality due to the influence of contact impedance.

In the bioimpedance measurement device of one embodiment,
The error detection part
A reference voltage supply unit that supplies a lower limit voltage and an upper limit voltage that define the allowable supply voltage range or the allowable input voltage range;
The supply voltage to the first electrode or the second electrode from the constant current unit or the input voltage to the differential amplifier circuit from the third electrode or the fourth electrode is the lower limit from the reference voltage supply unit. A first comparator that outputs a signal indicating that there is a contact error when the voltage falls below;
The supply voltage to the first electrode or the second electrode from the constant current unit or the input voltage to the differential amplifier circuit from the third electrode or the fourth electrode is the upper limit from the reference voltage supply unit. And a second comparator that outputs a signal indicating that there is a contact error when the voltage exceeds the voltage.

  In the bioimpedance measuring apparatus according to the embodiment, the reference voltage supply unit included in the error detection unit supplies the lower limit voltage and the upper limit voltage that define the allowable supply voltage range or the allowable input voltage range. The first comparator is configured such that the supply voltage from the constant current unit to the first electrode or the second electrode or the input voltage from the third electrode or the fourth electrode to the differential amplifier circuit is the reference voltage. When the voltage falls below the lower limit voltage from the supply unit, a signal indicating the presence of the contact error is output. Further, the second comparator is configured such that the supply voltage from the constant current section to the first electrode or the second electrode or the input voltage from the third electrode or the fourth electrode to the differential amplifier circuit is When the upper limit voltage from the reference voltage supply unit is exceeded, a signal indicating the presence of the contact error is output. That is, the supply voltage from the constant current section to the first electrode or the second electrode or the input voltage from the third electrode or the fourth electrode to the differential amplifier circuit is both at the lower limit and the upper limit. Whether it is abnormal is detected. Therefore, it is possible to more appropriately detect an abnormality due to the influence of contact impedance.

In another aspect, the bioimpedance measurement device of the present invention is:
A first electrode and a second electrode to be brought into contact with the living body, respectively, and a third electrode and a fourth electrode to be brought into contact with portions corresponding to the first electrode and the second electrode in the living body,
A constant current section for supplying a predetermined alternating current to the living body via the first electrode and the second electrode;
A voltage measuring unit including a differential amplifier circuit that differentially amplifies a voltage drop caused by the alternating current flowing through the living body through the third electrode and the fourth electrode;
When a distortion amount representing the degree to which the output signal of the differential amplifier circuit is distorted with respect to the sine wave is calculated, and the distortion amount exceeds a predetermined allowable range, the living body, the first electrode, and the second electrode And an error detection unit that determines that there is a contact error between the electrode, the third electrode, and the fourth electrode.

  In the bioimpedance measuring apparatus according to the present invention, the constant current section causes a predetermined alternating current to flow through the living body via the first electrode and the second electrode. The voltage measurement unit measures a voltage drop caused by the alternating current flowing through the living body via the third electrode and the fourth electrode. Specifically, a differential amplifier circuit included in the voltage measuring unit differentially amplifies the voltage drop. The voltage drop is measured by rectifying, smoothing, and A / D converting the output of the differential amplifier circuit. The impedance of the living body is obtained by converting the voltage drop measured by the voltage measuring unit into a numerical value (dividing by the energizing current). On the other hand, the error detection unit calculates a distortion amount indicating the degree to which the output signal of the differential amplifier circuit is distorted with respect to the sine wave, and when the distortion amount exceeds a predetermined allowable range, It is determined that there is a contact error between the first electrode, the second electrode, the third electrode, and the fourth electrode. The determination result related to the contact error is obtained in real time based on the amount of distortion with respect to the sine wave of the output signal of the differential amplifier circuit, separately from the measurement result related to the impedance. Therefore, according to this bioimpedance measuring apparatus, it is possible to appropriately detect abnormality due to the influence of contact impedance.

In the bioimpedance measurement device of one embodiment,
The error detection part
A sampling unit that samples the output signal of the differential amplifier circuit at a cycle shorter than the cycle of the alternating current and obtains it as sampling data;
A sampling data storage unit for temporarily storing sampling data acquired by the sampling unit;
A distortion amount calculation unit that calculates the distortion amount using the sampling data stored by the sampling data storage unit.

  In the bioimpedance measurement apparatus of this embodiment, the sampling unit included in the error detection unit samples the output signal of the differential amplifier circuit at a cycle shorter than the cycle of the alternating current as sampling data. get. The sampling data storage unit stores at least temporarily the sampling data acquired by the sampling unit. The distortion amount calculation unit calculates the distortion amount using the sampling data stored in the sampling data storage unit. Therefore, the distortion amount with respect to the sine wave of the output signal of the differential amplifier circuit is calculated with high accuracy. Therefore, it is possible to more appropriately detect an abnormality due to the influence of contact impedance.

In the bioimpedance measurement device of one embodiment,
The distortion amount calculation unit
A first sampling time and a first sampling voltage value corresponding to the maximum point of the output signal of the differential amplifier circuit are extracted from the sampling data, and correspond to the minimum point of the output signal of the differential amplifier circuit. Extracting a second sampling time and a second sampling voltage value, and further extracting a third sampling voltage value obtained at an intermediate time between the first sampling time and the second sampling time;
A deviation amount of the third sampling voltage value with respect to an average value of the first sampling voltage value and the second sampling voltage value is calculated as the distortion amount.

  In the bioimpedance measuring apparatus according to the embodiment, the distortion amount calculation unit obtains, from the sampling data, a first sampling time corresponding to the maximum point of the output signal of the differential amplifier circuit and a first sampling voltage value. And extracting a second sampling time and a second sampling voltage value corresponding to the minimum point of the output signal of the differential amplifier circuit, and further, between the first sampling time and the second sampling time. A third sampling voltage value obtained at the intermediate time is extracted. Then, the distortion amount calculation unit calculates a deviation amount of the third sampling voltage value with respect to an average value of the first sampling voltage value and the second sampling voltage value as the distortion amount. Thereby, the amount of distortion is calculated.

In the bioimpedance measurement device of one embodiment,
The distortion amount calculation unit
A first sampling time and a first sampling voltage value corresponding to the maximum point of the output signal of the differential amplifier circuit are extracted from the sampling data, and correspond to the minimum point of the output signal of the differential amplifier circuit. Extracting a second sampling time and a second sampling voltage value, and further extracting a third sampling time giving an intermediate voltage between the first sampling voltage value and the second sampling voltage value;
A deviation amount of the third sampling time with respect to an average value of the first sampling time and the second sampling time is calculated as the distortion amount.

  In the bioimpedance measuring apparatus according to the embodiment, the distortion amount calculation unit obtains, from the sampling data, a first sampling time corresponding to the maximum point of the output signal of the differential amplifier circuit and a first sampling voltage value. And extracting a second sampling time and a second sampling voltage value corresponding to a minimum point of the output signal of the differential amplifier circuit, and further extracting the first sampling voltage value and the second sampling voltage value. A third sampling time that provides an intermediate voltage is extracted. The distortion amount calculation unit calculates a deviation amount of the third sampling time with respect to an average value of the first sampling time and the second sampling time as the distortion amount. Thereby, the amount of distortion is calculated.

In the bioimpedance measurement device of one embodiment,
The distortion amount calculation unit
A first sampling time and a first sampling voltage value corresponding to the maximum point of the output signal of the differential amplifier circuit are extracted from the sampling data, and correspond to the minimum point of the output signal of the differential amplifier circuit. Extract the second sampling time and the second sampling voltage value to be
The difference between the first sampling voltage value and the second sampling voltage value is an amplitude, has the same period as the period of the alternating current, and an average of the first sampling voltage value and the second sampling voltage value Set the sine wave whose value is a DC component,
A deviation amount of the sampling voltage value of the output signal of the differential amplifier circuit with respect to the voltage value of the sine wave is calculated as the distortion amount at each sampling time.

  In the bioimpedance measuring apparatus according to the embodiment, the distortion amount calculation unit obtains, from the sampling data, a first sampling time corresponding to the maximum point of the output signal of the differential amplifier circuit and a first sampling voltage value. In addition to extraction, a second sampling time and a second sampling voltage value corresponding to the minimum point of the output signal of the differential amplifier circuit are extracted. Subsequently, the distortion amount calculation unit sets the amplitude of ½ of the difference between the first sampling voltage value and the second sampling voltage value, and has the same cycle as the cycle of the alternating current, and the first sampling voltage. The sine wave having the average value of the value and the second sampling voltage value as a DC (direct current) component is set. The distortion amount calculation unit calculates, as the distortion amount, a deviation amount of the sampling voltage value of the output signal of the differential amplifier circuit with respect to the voltage value of the sine wave at each sampling time. Thereby, the amount of distortion is calculated.

  In the bioelectrical impedance measuring apparatus according to one embodiment, the strain amount calculation unit averages the strain amount over a predetermined period including a plurality of sampling times, and the average value of the obtained strain amount is set as a second strain amount. It is characterized by doing.

  In the bioimpedance measurement apparatus according to the embodiment, the distortion amount calculation unit averages the distortion amount over a predetermined period including a plurality of sampling times, and obtains the average value of the obtained distortion amounts as a second distortion amount. And When the second distortion amount exceeds a predetermined allowable range, the error detection unit has a contact error between the living body and the first electrode, the second electrode, the third electrode, and the fourth electrode. judge. Therefore, for example, even when the contact error is not detected in the determination at each sampling time, the contact error can be detected based on the second distortion amount. Therefore, it is possible to more appropriately detect an abnormality due to the influence of contact impedance.

  As is clear from the above, according to the bioimpedance measuring apparatus of the present invention, an abnormality due to the influence of contact impedance can be detected appropriately.

It is a figure which shows the circuit structure of the bioimpedance measuring apparatus of one Embodiment of this invention. It is a figure which shows the circuit structure of the modification which deform | transformed the bioimpedance measuring apparatus of FIG. It is a figure which shows the voltage waveform detected by the error detection part of the said bioimpedance measuring apparatus. It is a figure which shows the point sampled by the error detection part of the bioimpedance measuring apparatus of another embodiment of this invention. It is a figure which shows the circuit structure of the bioimpedance measuring apparatus of another embodiment of this invention. It is a figure which shows the circuit structure of the modification which deform | transformed the bioimpedance measuring apparatus of FIG. FIG. 7A is a diagram illustrating a voltage waveform detected by the error detection unit of the bioimpedance measurement apparatus when there is no contact impedance between the electrode and the living body. FIG. 7B is a diagram illustrating a voltage waveform detected by the error detection unit of the bioimpedance measurement apparatus when there is a contact impedance between the electrode and the living body. It is a figure which illustrates the data table obtained by sampling by the said error detection part. It is a figure which graphs and shows how to detect the contact error based on the difference between the sampling data in the data table and the sine wave. It is a figure explaining the method of the detection of the further contact error based on the difference between the sampling data in the said data table, and a sine wave. FIG. 11A is a diagram illustrating the appearance of a general bioelectrical impedance measuring apparatus. FIG. 11B is a diagram illustrating a circuit configuration of a general bioimpedance measuring apparatus.

(First embodiment)
FIG. 1 shows a circuit configuration of a bioimpedance measuring apparatus (the whole is denoted by reference numeral 91) according to an embodiment of the present invention.

  This bioimpedance measurement apparatus 91 is similar to the general bioimpedance measurement apparatus shown in FIG. 11B, on the first electrode 1 to be brought into contact with the toe side 901 of the left foot of the living body 900 and on the toe side 902 of the right foot. The second electrode 2 to be contacted, the third electrode 3 to be in contact with the left foot heel 903, and the fourth electrode 4 to be in contact with the right foot heel 904 are provided. These electrodes 1, 2, 3, and 4 are provided on the mounting plate 10 shown in FIG.

  The bioelectrical impedance measuring device 91 includes a constant current source 20 as a constant current unit and a voltage measuring unit 21.

  In this example, the constant current source 20 includes two supply terminals 20a and 20b that are both ungrounded. The supply terminal 20 a is connected to the first electrode 1, and the supply terminal 20 b is connected to the second electrode 2. The constant current source 20 causes a predetermined alternating current I to flow through the living body 900 within the maximum supply voltage range from the supply terminal 20a through the first electrode 1 and from the supply terminal 20b through the second electrode 2 (this In the example, the frequency is 50 [kHz].) In this example, the maximum supply voltage range of the constant current source 20 is a voltage range between the ground voltage GND (= 0 [V]) and the voltage Vcc (= 4.0 [V]) shown in FIG. . When the contact impedances FILR and FIRR between the electrodes 1 and 2 and the living body 900 are small and there is no contact error, the voltage waveform of the supply terminal 20b becomes a sine wave as shown by a broken line Wn in FIG. On the other hand, when the contact impedances FILR and FIRR between the electrodes 1 and 2 and the living body 900 are large and there is a contact error, the voltage waveform of the supply terminal 20b is the maximum supply as shown by the solid line Ws in FIG. The peak portion exceeding the voltage range (GND, Vcc) is a saturated waveform.

  The voltage measuring unit 21 shown in FIG. 1 includes a differential amplifier circuit 22, a rectifier circuit 23, a smoothing circuit 24, and an A / D conversion circuit 25. The differential amplifier circuit 22 includes a first input terminal 22a connected to the third electrode 3, a second input terminal 22b connected to the fourth electrode 4, and an output terminal 22c. The differential amplifier circuit 22 receives the voltage V1 from the third electrode 3 through the first input terminal 22a, and receives the voltage V2 from the fourth electrode 4 through the second input terminal 22b. The difference between the voltage V1 and the voltage V2 is scheduled to be within a predetermined maximum input voltage range (dynamic range). Then, the differential amplifier circuit 22 amplifies the difference between the voltage V1 and the voltage V2, and outputs an output signal Vo1 representing the amplification result to the output terminal 22c. The rectifier circuit 23 rectifies the output signal Vo1 of the differential amplifier circuit 22. The smoothing circuit 24 includes an RC integration circuit (not shown) and smoothes the output of the rectifier circuit 23. The A / D conversion circuit 25 performs A / D conversion on the output of the smoothing circuit 24 and outputs it as a digital signal Vo2.

  Furthermore, the bioelectrical impedance measuring device 91 includes an error detection unit 40. The error detection unit 40 includes a first comparator 41, a second comparator 42, and two reference power sources 43 and 44 as reference voltage supply units. The reference power supply 43 supplies a lower limit voltage Vref1 (= 0.3 [V]) that defines an allowable supply voltage range. The reference power supply 43 supplies an upper limit voltage Vref2 (= 3.7 [V]) that defines an allowable supply voltage range. As can be seen, the allowable input voltage range (Vref1, Vref2) is set within the maximum input voltage range (GND, Vcc).

  The first comparator 41 includes a non-inverting input terminal 41 a connected to one supply terminal 20 b of the constant current source 20, an inverting input terminal 41 b that receives the lower limit voltage Vref 1 from the reference power supply 43, and an output terminal 41 c. ing. The first comparator 41 outputs a signal AL1 indicating whether the voltage received at the non-inverting input terminal 41a is larger than the lower limit voltage Vref1 to the output terminal 41c. If the voltage received at the non-inverting input terminal 41a is equal to or higher than the lower limit voltage Vref1, the signal AL1 becomes a signal of logical value 1 indicating that there is no contact error, while the voltage received at the non-inverting input terminal 41a is lower than the lower limit voltage Vref1. If the voltage is lower than the voltage Vref1, the signal becomes a logical value 0 indicating that there is a contact error.

  The second comparator 42 includes an inverting input terminal 42a connected to one supply terminal 20b of the constant current source 20, a non-inverting input terminal 42b that receives the upper limit voltage Vref2 from the reference power supply 44, and an output terminal 42c. ing. The second comparator 42 outputs a signal AH1 indicating whether or not the voltage received at the inverting input terminal 42a is smaller than the upper limit voltage Vref2 to the output terminal 42c. If the voltage received at the inverting input terminal 42a is equal to or lower than the upper limit voltage Vref2, the signal AH1 becomes a signal of logical value 1 indicating that there is no contact error, while the voltage received at the inverting input terminal 42a is the upper limit voltage Vref2. If it exceeds, a signal of logical value 0 indicating that there is a contact error is obtained.

  The control unit 30 calculates the impedance and body composition value based on the signal Vo2 from the voltage measurement unit 21, creates a signal to be displayed on the display unit 22, and performs operations of the entire bioimpedance measurement apparatus. Control.

  The bioimpedance measuring device 91 operates as follows as a whole.

  First, when the left and right soles of the living body 900 are placed on the mounting plate 10, the constant current source 20 causes a predetermined alternating current I to flow through the living body 900 via the first electrode 1 and the second electrode 2. The voltage measurement unit 21 measures the voltage drop V generated by the alternating current I flowing through the living body 900 via the third electrode 3 and the fourth electrode 4. Specifically, the differential amplifier circuit 22 included in the voltage measuring unit 21 inputs the drop voltage V within the maximum input voltage range and differentially amplifies it. The output signal Vo1 of the differential amplifier circuit 22 is rectified by the rectifier circuit 23, the smoothing circuit 24 is smoothed, and the A / D conversion circuit 25 is A / D converted into a digital signal Vo2. A drop voltage V is obtained according to the digital signal Vo2. The control unit 30 obtains the impedance of the living body by converting this voltage drop V into a numerical value (dividing by the energization current).

  Here, if the error detection unit 40 in FIG. 1 outputs a signal of logical value 1 indicating that there is no contact error as the signals AL1 and AH2, the control unit 30 is calculated based on the impedance. The body composition value is displayed on the display unit 22 (see FIG. 11A).

  In the error detection unit 40 in FIG. 1, the supply voltage (the voltage at one supply terminal 20b of the constant current source 20) from the constant current source 20 to the second electrode 2 is set within the maximum input voltage range (GND, Vcc). When the allowable supply voltage range (Vref1, Vref2) is exceeded, a signal indicating that there is a contact error between the living body 900 and the electrodes 1, 2 is output. Specifically, when the voltage at one supply terminal 20b of the constant current source 20 falls below the lower limit voltage Vref1, a signal of logical value 0 indicating that there is a contact error is output as the signal AL1. When the voltage at one supply terminal 20b of the constant current source 20 exceeds the upper limit voltage Vref2, a signal having a logical value 0 indicating that there is a contact error is output as the signal AH1.

  If either one or both of the signals AL1 and AH2 are signals having a logical value 0 indicating that there is a contact error, the control unit 30 displays a message indicating that there is a contact error instead of the body composition value. And displayed on the display unit 22 (see FIG. 11A).

  In this bioimpedance measurement device 91, the determination result related to the contact error is a supply voltage to the second electrode 2 from the constant current source 20 (the voltage at one supply terminal 20b of the constant current source 20) separately from the measurement result related to the impedance. Is obtained in real time based on whether or not the allowable supply voltage range (Vref1, Vref2) for the constant current source 20 has been exceeded before the saturation of the constant current source 20. Therefore, according to this bioimpedance measuring apparatus 91, an abnormality due to the influence of contact impedance can be detected appropriately.

  In particular, in this bioimpedance measuring device 91, the supply voltage from the constant current source 20 to the second electrode 2 (the voltage at one supply terminal 20b of the constant current source 20) is abnormal both at the lower limit and the upper limit. Is detected. Therefore, it is possible to more appropriately detect an abnormality due to the influence of contact impedance.

  In this example, the error detection unit 40 detects the voltage of one supply terminal 20b of the constant current source 20, but is not limited to this, and detects the voltage of the other supply terminal 20a of the constant current source 20. May be. Even in that case, an abnormality caused by the influence of the contact impedance can be appropriately detected by the same operation.

  If the constant current source 20 is of a type in which the two supply terminals are not ungrounded but one supply terminal is grounded (or the voltage is fixed), the error detection unit 40 is already What is necessary is just to detect the voltage of one supply terminal (terminal from which a voltage changes). Thereby, an abnormality due to the influence of contact impedance can be detected appropriately.

  FIG. 2 shows a circuit configuration of a modified example (the whole is denoted by reference numeral 92) obtained by modifying the bioimpedance measuring apparatus 91 of FIG.

  In this bioimpedance measuring device 92, the non-inverting input terminal 41 a of the first comparator 41 and the inverting input terminal 42 a of the second comparator 42 of the error detection unit 40 are both the second input terminal 22 b of the differential amplifier circuit 22. It is connected to the. That is, in this bioimpedance measuring device 92, the error detection unit 40 is connected to the second input terminal 22 b (fourth electrode 4) of the differential amplifier circuit 22 instead of the voltage of one supply terminal 20 b of the constant current source 20. ) Is detected.

  In this example, the maximum input voltage range (dynamic range) of the differential amplifier circuit 22 is between the ground voltage GND (= 0 [V]) and the voltage Vcc (= 4.0 [V]) shown in FIG. Voltage range. When the contact impedances FILR, FIRR, FVLR, and FVRR between the electrodes 1, 2, 3, 4 and the living body 900 are small and there is no contact error, the voltage waveform of the second input terminal 22b is a broken line in FIG. It becomes a sine wave as indicated by Wn. On the other hand, when the contact impedances FILR, FIRR, FVLR, and FVRR between the electrodes 1 and 2 and the living body 900 are large and there is a contact error, the voltage waveform of the second input terminal 22b is a solid line Ws in FIG. As shown, a peak portion exceeding the maximum input voltage range (GND, Vcc) is saturated. As can be seen, the allowable input voltage ranges (Vref1, Vref2) are set within the maximum input voltage range (GND, Vcc).

  The first comparator 41 of the error detector 40 shown in FIG. 2 has a contact error as the signal AL1 when the input voltage V2 to the second input terminal 22b of the differential amplifier circuit 22 is lower than the lower limit voltage Vref1. A signal having a logical value of 0 is output. On the other hand, if the input voltage V2 is equal to or higher than the lower limit voltage Vref1, the first comparator 41 outputs a signal having a logical value 1 indicating that there is no contact error as the signal AL1. Further, the second comparator 42 outputs a signal of logical value 0 indicating that there is a contact error as the signal AH1 when the input voltage V2 to the second input terminal 22b of the differential amplifier circuit 22 exceeds the upper limit voltage Vref2. Output. If the input voltage V2 is equal to or lower than the upper limit voltage Vref2, the second comparator 42 outputs a signal having a logical value 1 indicating that there is no contact error as the signal AH1.

  In this bioimpedance measurement device 92, the determination result regarding the contact error is that the allowable input voltage range (Vref1) of the differential amplifier circuit 22 is the stage before the input voltage V2 to the second input terminal 22b of the differential amplifier circuit 22 is saturated. , Vref2) is obtained in real time. Therefore, according to this bioimpedance measuring apparatus 92, an abnormality due to the influence of contact impedance can be detected appropriately.

  In particular, in this bioimpedance measuring apparatus 92, it is detected whether or not the input voltage V2 to the second input terminal 22b of the differential amplifier circuit 22 is abnormal at both the lower limit and the upper limit. Therefore, it is possible to more appropriately detect an abnormality due to the influence of contact impedance.

  In this example, the error detection unit 40 detects the input voltage V2 to the second input terminal 22b of the differential amplifier circuit 22. However, the present invention is not limited to this, and the first input terminal 22a of the differential amplifier circuit 22 is not limited thereto. The input voltage V1 may be detected. Even in that case, an abnormality caused by the influence of the contact impedance can be appropriately detected by the same operation.

  Further, the error detection unit 40 in FIG. 1 that detects the voltage of one supply terminal 20b (or the other supply terminal 20a) of the constant current source 20, and the input voltage to the second input terminal 22b of the differential amplifier circuit 22 You may provide both with the error detection part 40 in FIG. 2 which detects V2 (or input voltage V1 to the 1st input terminal 22a). Thereby, an abnormality due to the influence of contact impedance can be detected with higher accuracy. The number of error detection units 40 is preferably set according to the required accuracy.

(Second Embodiment)
FIG. 5 shows a circuit configuration of a bioimpedance measuring apparatus (the whole is denoted by reference numeral 93) according to another embodiment of the present invention. For ease of understanding, in FIG. 5, the same components as those in FIG. 1 are denoted by the same reference numerals.

  This bioimpedance measurement device 93 is connected to the first electrode 1 to be brought into contact with the toe side 901 of the left foot of the living body 900 and the toe side 902 of the right foot similarly to the general bioimpedance measurement device shown in FIG. The second electrode 2 to be contacted, the third electrode 3 to be in contact with the left foot heel 903, and the fourth electrode 4 to be in contact with the right foot heel 904 are provided. These electrodes 1, 2, 3, and 4 are provided on the mounting plate 10 shown in FIG.

  The bioimpedance measuring device 93 includes a constant current source 20 as a constant current unit, a voltage measuring unit 21 ′, and an error detecting unit 50.

  The constant current source 20 causes a predetermined alternating current I to flow through the living body 900 within the maximum supply voltage range from the supply terminal 20a through the first electrode 1 and from the supply terminal 20b through the second electrode 2 (this In the example, the frequency is 50 kHz.)

  The voltage measurement unit 21 ′ includes a differential amplifier circuit 22, an A / D conversion unit 32, a rectification processing unit 33, a smoothing processing unit 34, and a voltage detection unit 35. The differential amplifier circuit 22 includes a first input terminal 22a connected to the third electrode 3, a second input terminal 22b connected to the fourth electrode 4, and an output terminal 22c. The differential amplifier circuit 22 receives the voltage V1 from the third electrode 3 through the first input terminal 22a and receives the voltage V2 from the fourth electrode 4 through the second input terminal 22b. The difference between V1 and voltage V2 is amplified, and an output signal Vo1 representing the amplification result is output to the output terminal 22c. The A / D converter 32 performs A / D conversion on the output signal Vo1 of the differential amplifier circuit 22 and outputs it as a digital signal Vo1 ′. The rectification processing unit 33 rectifies the output signal Vo1 ′ of the A / D conversion unit 32. In this example, it is assumed that full-wave rectification is performed on the rectification processing unit 33, and in the following description, the half-wave portion of the obtained waveform is inverted and all waves are continuous. The smoothing processing unit 34 smoothes the output of the rectification processing unit 33. The voltage detection unit 35 outputs a voltage value Vo2 corresponding to the output of the smoothing processing unit 34. A drop voltage V is determined according to this voltage value Vo2.

  The control unit 30 obtains the impedance of the living body by converting this voltage drop V into a numerical value (dividing by the energization current).

  Here, when the contact impedances FILR, FIRR, FVLR, FVRR between the electrodes 1, 2, 3, 4 and the living body 900 are small and there is no contact error, the voltage V1 from the third electrode 3 and the fourth electrode The voltage V2 from 4 becomes a sine wave as indicated by a broken line and a one-dot chain line in FIG. As a result, the output signal Vo1 of the differential amplifier circuit 22 also becomes a sine wave as shown by the solid line in FIG. On the other hand, when the contact impedance FILR, FIRR, FVLR, FVRR between the electrodes 1, 2, 3, 4 and the living body 900 is large and there is a contact error, the voltage V1 from the third electrode 3 and the fourth electrode 4 The voltage V2 from is a distorted waveform as shown by a broken line and a one-dot chain line in FIG. As a result, the output signal Vo1 of the differential amplifier circuit 22 also has a distorted waveform as shown by the solid line in FIG.

  The error detection unit 50 shown in FIG. 5 includes a sampling unit 51, a sampling data storage unit 52, a distortion amount calculation unit 53, and a contact error determination unit 54. The sampling unit 51 is substantially equivalent to the output signal Vo1 ′ of the A / D conversion unit 32 (except for the difference between the analog signal and the digital signal). "Output signal Vo1 'of the differential amplifier circuit 22") is sampled at a cycle sufficiently shorter than the cycle of the alternating current I (in this example, 500 [kHz]) and acquired as sampling data. It is desirable to set the sampling period according to the required accuracy. If the required accuracy is high, the sampling period may be set shorter. The sampling data storage unit 52 stores the sampling data acquired by the sampling unit 51 at least temporarily. The distortion amount calculation unit 53 uses the sampling data stored in the sampling data storage unit 52 to calculate a distortion amount indicating the degree to which the output signal Vo1 ′ of the differential amplifier circuit is distorted with respect to the sine wave. The contact error determination unit 54 determines that there is a contact error between the living body 900 and the electrodes 1, 2, 3, 4 when the strain amount calculated by the strain amount calculation unit 53 exceeds a predetermined allowable range. , A signal of logical value 1 indicating that there is a contact error is output as the signal AS1. On the other hand, if the distortion amount calculated by the distortion amount calculation unit 53 is within a predetermined allowable range, the contact error determination unit 54 outputs a signal of logical value 0 indicating that there is no contact error as the signal AS1.

  Note that the A / D conversion unit 32, the rectification processing unit 33, the smoothing processing unit 34 and the voltage detection unit 35 of the voltage measurement unit 21 ′, the sampling unit 51 of the error detection unit 50, the distortion amount calculation unit 53, and the contact error determination unit. 54 is configured by a CPU and software (not shown) of the control unit 30. The sampling data storage unit 52 is constituted by, for example, a RAM (Random Access Memory). As will be appreciated by those skilled in the art, the bioimpedance measuring device 93 does not require new component costs as compared to a general bioimpedance measuring device. Further, the apparatus can be configured in a small size.

  In this bioimpedance measuring apparatus 93, the determination result regarding the contact error is obtained in real time based on the distortion amount of the output signal Vo1 ′ of the differential amplifier circuit 22 with respect to the sine wave, separately from the measurement result regarding the impedance. Therefore, according to this bioimpedance measuring apparatus 93, an abnormality due to the influence of contact impedance can be detected appropriately.

  Next, how to calculate the distortion amount and determine the contact error will be described with reference to four specific examples. It should be noted that an ideal sine wave serving as a reference for calculating the distortion amount is Vs = AmSIN (2πft), where the amplitude is Am, the frequency is f, the time is t, and the offset voltage (DC component) is Vdc (constant). It shall be represented by + Vdc. In this example, the frequency f is fixed according to the AC frequency of the constant current source 20, and f = 50 [kHz].

(Specific example 1)
In this example, as shown in FIG. 4, the distortion amount calculation unit 53 uses the first sampling time T1 and the first sampling corresponding to the maximum point (mountain) of the output signal Vo1 ′ of the differential amplifier circuit 22 from the sampling data. The voltage value P1 is extracted, and the second sampling time T2 and the second sampling voltage value P2 corresponding to the minimum point (valley) of the output signal Vo1 ′ of the differential amplifier circuit 22 are extracted. Further, a third sampling voltage value Vx obtained at an intermediate time Tx = (T1 + T2) / 2 between the first sampling time T1 and the second sampling time T2 is extracted from the sampling data.

  At the same time, the distortion amount calculation unit 53 calculates the deviation amount | Vx− (P1 + P2) / 2 | of the third sampling voltage value Vx with respect to the average value (P1 + P2) / 2 of the first sampling voltage value and the second sampling voltage value. Calculated as the amount of distortion.

  Next, the contact error determination unit 54 determines whether or not there is a contact error depending on whether the strain amount | Vx− (P1 + P2) / 2 | is larger or smaller than a threshold value (Vth1) according to the required accuracy. judge. That is, if | Vx− (P1 + P2) / 2 | ≧ Vth1, it is determined that there is a contact error. If | Vx− (P1 + P2) / 2 | <Vth1, it is determined that there is no contact error.

  Here, the threshold value Vth1 is calculated by, for example, calculating the amplitude Am of the output signal Vo1 ′ of the differential amplifier circuit 22 as Am = (P1−P2) / 2, and a value of 10% of the amplitude Am (for example, 0.1 [V ]).

  Alternatively, the distortion amount calculation unit 53 may calculate the time-based distortion amount as follows instead of the voltage-based distortion amount described above.

  That is, the distortion amount calculation unit 53 extracts the first sampling time T1 and the first sampling voltage value P1 corresponding to the maximum point (mountain) of the output signal Vo1 ′ of the differential amplifier circuit 22 from the sampling data, A second sampling time T2 and a second sampling voltage value P2 corresponding to the minimum point (valley) of the output signal Vo1 ′ of the differential amplifier circuit 22 are extracted. Further, a third sampling time Tx that provides an intermediate voltage (P1 + P2) / 2 between the first sampling voltage value P1 and the second sampling voltage value P2 is extracted from the sampling data. Then, the distortion amount calculation unit 53 distorts the deviation amount | Tx− (T1 + T2) / 2 | of the third sampling time Tx with respect to the average value (T1 + T2) / 2 of the first sampling time T1 and the second sampling time T2. Calculate as a quantity.

  Next, the contact error determination unit 54 determines whether or not there is a contact error depending on whether the strain amount | Tx− (T1 + T2) / 2 | is larger or smaller than a threshold value (Tth1) according to the required accuracy. judge. That is, if | Tx− (T1 + T2) / 2 | ≧ Tth1, it is determined that there is a contact error. If | Tx− (T1 + T2) / 2 | <Tth1, it is determined that there is no contact error.

  Here, the threshold value Tth1 is determined to be, for example, a value (for example, 0.002 [msec]) of 10% of the period of the output signal Vo1 ′ of the differential amplifier circuit 22.

  According to this specific example 1, the presence or absence of a contact error can be determined by a relatively simple calculation.

(Specific example 2)
In this example, as shown in FIG. 4, the distortion amount calculation unit 53 uses the first sampling time T1 and the first sampling corresponding to the maximum point (mountain) of the output signal Vo1 ′ of the differential amplifier circuit 22 from the sampling data. The voltage value P1 is extracted, and the second sampling time T2 and the second sampling voltage value P2 corresponding to the minimum point (valley) of the output signal Vo1 ′ of the differential amplifier circuit 22 are extracted. Further, the third sampling time T3 and the third sampling voltage value P3 corresponding to the maximum point (mountain) of the output signal Vo1 ′ of the differential amplifier circuit 22 are extracted from the sampling data. In this way, the n-th sampling time Tn and the third sampling voltage value Pn for each pole are sequentially extracted (where n is a natural number of 3 or more). Each pole is represented as (T1, P1), (T2, P2), ..., (Tn, Pn).

  At the same time, the distortion amount calculation unit 53 calculates the amplitude difference | P1-P2 | between adjacent poles (T1, P1) and (T2, P2), and also sets the adjacent poles (T2, P2), The amplitude difference | P2-P3 | between (T3, P3) is calculated. In this way, the amplitude difference between the adjacent poles is calculated sequentially.

  Further, the distortion amount calculation unit 53 calculates the difference between the amplitude differences | P1-P2 |, | P2-P3 |,... Between adjacent poles and the amplitude difference between adjacent poles of an ideal sine wave. The difference is calculated as a distortion amount.

  Then, the contact error determination unit 54 determines the presence or absence of a contact error depending on whether the amount of distortion is larger or smaller than a threshold (Vth2) according to the required accuracy.

  The distortion amount calculation unit 53 calculates the difference between the amplitude differences | P1-P2 |, | P2-P3 |,... As the distortion amount, and the contact error determination unit 54 determines the variation between the distortion amounts. However, the presence or absence of a contact error may be determined depending on whether it is larger or smaller than a threshold (Vth2 ′) according to the required accuracy. Further, the determination of the presence / absence of a contact error based on the threshold value Vth2 and the determination of the presence / absence of a contact error based on the threshold value Vth2 ′ may be used in combination.

  Alternatively, the distortion amount calculation unit 53 may calculate the time-based distortion amount as follows instead of the voltage-based distortion amount described above.

  That is, the distortion amount calculation unit 53 calculates the time difference | T1−T2 | between the adjacent extreme points (T1, P1) and (T2, P2), and the adjacent extreme points (T2, P2), (T3). , P3) is calculated as a time difference | T2-T3 |. In this way, the time difference between the adjacent extreme points is sequentially calculated.

  Further, the distortion amount calculation unit 53 calculates the difference between the time differences | T1-T2 |, | T2-T3 |,... Between the adjacent poles and the time difference between the adjacent poles of the ideal sine wave. Calculated as the amount of distortion.

  Then, the contact error determination unit 54 determines the presence or absence of a contact error depending on whether the amount of distortion is larger or smaller than a threshold (Tth2) according to the required accuracy.

  Note that the distortion amount calculation unit 53 calculates the difference between | T1-T2 |, | T2-T3 |,... As a distortion amount, and the contact error determination unit 54 calculates the variation between the distortion amounts. The presence / absence of a contact error may be determined according to whether it is larger or smaller than a threshold value (Tth2 ′) according to the required accuracy. Further, the determination of the presence / absence of a contact error based on the threshold value Tth2 and the determination of the presence / absence of a contact error based on the threshold value Tth2 ′ may be used in combination.

  In this specific example 2, the amount of distortion is defined using the amplitude difference or time difference between adjacent poles, but the amount of distortion may also be defined using the amplitude difference and time difference between poles that are further away from each other. good.

(Specific example 3)
In this example, the sampling data obtained by sampling by the sampling unit 51 is shown in the “time t [msec]” column and the “input data” column in the data table of FIG. It shall be remembered. Each sampling point is obtained by using the sampling time t _x [msec] stored in the “time t [msec]” column and the sampling voltage value V _x [V] stored in the “input data” column (t _x, it shall be expressed as _{V x).}

The distortion amount calculation unit 53 includes a voltage difference | V ₁ −V ₂ | between adjacent sampling points (t ₁ , V ₁ ) and (t ₂ , V ₂ ), a time difference | t ₁ −t ₂ |, The inclination | V ₁ −V ₂ | / | t ₁ −t ₂ | is calculated as the distortion amount. Further, a voltage difference | V ₂ −V ₃ | between adjacent sampling points (t ₂ , V ₂ ) and (t ₃ , V ₃ ), a time difference | t ₂ −t ₃ |, and an inclination as a distortion amount | V ₂ −V ₃ | / | t ₂ −t ₃ | In this manner, the voltage difference between the adjacent sampling points, the time difference, and the slope as the distortion amount are calculated sequentially.

  Then, the contact error determination unit 54 determines the presence or absence of a contact error depending on whether the amount of distortion (inclination) is larger or smaller than a threshold value (Vtth3) according to the required accuracy.

  Note that the threshold value Vtth3 is determined in advance according to the phase of each sampling point in an ideal sine wave.

(Specific example 4)
In this example, as in the above example, the sampling data obtained by sampling by the sampling unit 51 is input to the “time t [msec]” column in the data table of FIG. Assume that it is stored as shown in the “Data” column. Each sampling point is obtained by using the sampling time t _x [msec] stored in the “time t [msec]” column and the sampling voltage value V _x [V] stored in the “input data” column (t _x, expressed as _{V x).}

  The distortion amount calculation unit 53 extracts the first sampling time T1 and the first sampling voltage value P1 corresponding to the maximum point (mountain) of the output signal Vo1 ′ of the differential amplifier circuit 22 from the sampling data. A second sampling time T2 and a second sampling voltage value P2 corresponding to the minimum point (valley) of the output signal Vo1 ′ of the amplifier circuit 22 are extracted. In FIG. 8, sampling points corresponding to the maximum points (T1, P1) and sampling points corresponding to the minimum points (T2, P2) are shown from the outside.

  Here, as described above, an ideal sine wave serving as a reference for calculating the amount of distortion has an amplitude of Am, a frequency of f, a time of t, and an offset voltage (DC component) of Vdc (constant). , Vs = AmSIN (2πft) + Vdc. In this example, the frequency f is fixed according to the AC frequency of the constant current source 20, and f = 50 [kHz]. The amplitude Am is obtained as ½ of the difference between the first sampling voltage value P1 and the second sampling voltage value P2. That is, Am = | P1-P2 | / 2. The offset voltage (DC component) Vdc is obtained as an average value (P1 + P2) / 2 of the first sampling voltage value P1 and the second sampling voltage value P2. That is, Vdc = (P1 + P2) / 2. Thus, an ideal sine wave voltage value serving as a reference for calculating the amount of distortion is expressed as Vs = AmSIN (2πft) + Vdc.

The distortion amount calculator 53 calculates the voltage value Vs of the sine wave at each sampling time t _x as shown in the “Sine wave” column in FIG. The calculated voltage value Vs is stored in the “sine wave” column in the data table of FIG. At this time, the sampling point corresponding to the maximum point (T1, P1) and the sampling point corresponding to the minimum point (T2, P2) are used to match the phase of the sampling data with the phase of the sine wave. When a large number of data near the poles (T1, P1) and (T2, P2) are obtained, for example, the data is averaged to match the phase of the sampling data with the phase of the sine wave.

Further, the distortion amount calculation unit 53 calculates a deviation amount (V _x −Vs) of the sampling voltage value V _x of the output signal Vo1 ′ of the differential amplifier circuit 22 with respect to the voltage value Vs of the sine wave at each sampling time t _x. Calculated as the amount of distortion. The calculated distortion amount is stored in the “difference” column in the data table of FIG.

Then, the contact error determination unit 54 determines the presence or absence of a contact error depending on whether the amount of distortion is larger or smaller than a threshold (Vth4) according to the required accuracy. That is, if | V _x −Vs | ≧ Vth4, it is determined that there is a contact error. If | V _x −Vs | <Vth4, it is determined that there is no contact error.

  Here, the threshold value Vth4 is determined to be, for example, a value (for example, 0.100 [V]) of 10% of the amplitude Am of the output signal Vo1 ′ of the differential amplifier circuit 22.

FIG. 9 shows a sampling voltage value V _x (indicated by a symbol ◇ connected by a solid line Vo1 ′) at each sampling time t _x and a voltage value Vs of the sine wave (indicated by a symbol □ connected by a broken line D0). ) And the amount of deviation (V _x −Vs) (indicated by the symbol Δ connected by the solid line D1). In this example, the period until the sampling time _t x = _0.002~0.003 [msec], the period until the sampling time _t x = _0.008~0.011 [msec], the sampling time _t x = 0 | V _x −Vs | exceeds the threshold value Vth4 in the period from 017 to 0.018 [msec]. Therefore, the contact error determination unit 54 determines that there is a contact error.

Even if it is determined that | V _x −Vs | <Vth4 over one period and there is no contact error, as shown in FIG. In some cases, | V _x −Vs | may be close to the threshold value Vth4. In such a case, it is considered that it should be determined that there is a contact error.

Therefore, the distortion amount calculating section _53, (V x -Vs) a predetermined period including a plurality of sampling time _{t x,} for example, averaged over the 1/4 cycle every 1/4 period, resulting _{(V x} The average value of −Vs) is calculated as the second distortion amount (represented by Ave (V _x −Vs)).

The contact error determination unit 54 determines the presence or absence of a contact error depending on whether the second distortion amount Ave (V _x −Vs) is larger or smaller than a threshold value (Vth5) according to the required accuracy. . That is, if | Ave (V _x −Vs) | ≧ Vth5, it is determined that there is a contact error. If | Ave (V _x −Vs) | <Vth5, it is determined that there is no contact error.

  Here, the threshold value Vth5 is determined so that Vth5 <Vth4. In this example, Vth5 = 0.050 [V].

In this case, for example, even if a contact error is not detected in the determination at each sampling time t _x , the contact error can be detected based on the second distortion amount Ave (V _x −Vs). Therefore, it is possible to more appropriately detect an abnormality due to the influence of contact impedance.

  Note that the presence / absence of a contact error may be determined by combining some of the methods for calculating the distortion amount and determining the contact error described in the first to fourth specific examples.

  As described above, when the contact error determination unit 54 in FIG. 5 determines that there is a contact error between the living body 900 and the electrodes 1, 2, 3, and 4, the signal AS1 indicates that there is a contact error. A signal having a logical value of 1 is output. On the other hand, when it is determined that there is no contact error between the living body 900 and the electrodes 1, 2, 3, and 4, the contact error determination unit 54 outputs a signal of logical value 0 indicating that there is no contact error as the signal AS <b> 1. To do.

  If the contact error determination unit 54 outputs a signal having a logical value 0 indicating that there is no contact error as the signal AS1, the control unit 30 displays the body composition value calculated based on the impedance on the display unit 22 ( (See FIG. 11A).

  On the other hand, if the contact error determination unit 54 outputs a signal of logical value 1 indicating that there is a contact error, the control unit 30 displays a message indicating that there is a contact error instead of the body composition value. It is displayed on the part 22 (see FIG. 11A).

  In this embodiment, the rectification processing unit 33 is assumed to perform full-wave rectification, and the half-wave portion of the obtained waveform is inverted so that the full wave is continuous. When the rectification processing unit 33 performs half-wave rectification, the obtained half-wave waveform may be copied to make a full-wave portion, or the distortion amount may be calculated using a waveform for two waves.

  FIG. 6 shows a circuit configuration of a modified example (the whole is denoted by reference numeral 94) obtained by modifying the bioimpedance measuring apparatus 93 of FIG. In FIG. 6, the same components as those in FIG. 5 are denoted by the same reference numerals, and redundant description is omitted.

  This bioimpedance measurement device 94 corresponds to a device in which the order of the A / D conversion unit 32 and the rectification processing unit 33 in the bioimpedance measurement device 93 of FIG. That is, in this bioimpedance measuring apparatus 94, the rectifier circuit 23 is provided next to the differential amplifier circuit 22, and the A / D converter 32 is provided next to the rectifier circuit 23. The sampling unit 51 of the error detection unit 50 inputs the output signal of the A / D conversion unit 32.

  The bioimpedance measuring device 94 operates in the same manner as the bioimpedance measuring device 93 of FIG. 5 and has the same effects. That is, in this bioimpedance measuring apparatus 94, the determination result related to the contact error is obtained in real time based on the distortion amount of the output signal of the A / D conversion unit 32 with respect to the sine wave separately from the measurement result related to the impedance. Therefore, according to this bioimpedance measuring apparatus 94, an abnormality due to the influence of contact impedance can be detected appropriately.

  In the above embodiment, when there is a contact error, the bioimpedance measurement devices 91, 92, 93, and 94 display a message indicating that there is a contact error instead of the body composition value on the display unit 22 (FIG. 11A). ))). However, the present invention is not limited to this. For example, a speaker or a piezoelectric buzzer may be provided, and when there is a contact error, the user may be notified by voice or alarm sound.

20 constant current source 21 voltage measurement unit 30 control unit 40, 50 error detection unit 91, 92, 93, 94 bioimpedance measurement device

Claims (8)

A first electrode and a second electrode to be brought into contact with the living body, respectively, and a third electrode and a fourth electrode to be brought into contact with portions corresponding to the first electrode and the second electrode in the living body,
A constant current section for supplying a predetermined alternating current to the living body within a maximum supply voltage range via the first electrode and the second electrode;
A voltage measurement unit including a differential amplifier circuit that differentially amplifies a voltage drop caused by the alternating current flowing through the living body through the third electrode and the fourth electrode within a maximum input voltage range; ,
When the supply voltage from the constant current section to the first electrode or the second electrode exceeds the allowable supply voltage range set within the maximum supply voltage range, or the difference from the third electrode or the fourth electrode When the input voltage to the dynamic amplifier circuit exceeds the allowable input voltage range set within the maximum input voltage range, the living body and the first electrode, the second electrode, the third electrode, and the fourth electrode A bioimpedance measurement apparatus comprising: an error detection unit that determines that there is a contact error. The bioimpedance measurement apparatus according to claim 1,
The error detection part
A reference voltage supply unit that supplies a lower limit voltage and an upper limit voltage that define the allowable supply voltage range or the allowable input voltage range;
The supply voltage to the first electrode or the second electrode from the constant current unit or the input voltage to the differential amplifier circuit from the third electrode or the fourth electrode is the lower limit from the reference voltage supply unit. A first comparator that outputs a signal indicating that there is a contact error when the voltage falls below;
The supply voltage to the first electrode or the second electrode from the constant current unit or the input voltage to the differential amplifier circuit from the third electrode or the fourth electrode is the upper limit from the reference voltage supply unit. And a second comparator that outputs a signal indicating that the contact error is present when the voltage exceeds the voltage. A first electrode and a second electrode to be brought into contact with the living body, respectively, and a third electrode and a fourth electrode to be brought into contact with portions corresponding to the first electrode and the second electrode in the living body,
A constant current section for supplying a predetermined alternating current to the living body via the first electrode and the second electrode;
A voltage measuring unit including a differential amplifier circuit that differentially amplifies a voltage drop caused by the alternating current flowing through the living body through the third electrode and the fourth electrode;
When a distortion amount representing the degree to which the output signal of the differential amplifier circuit is distorted with respect to the sine wave is calculated, and the distortion amount exceeds a predetermined allowable range, the living body, the first electrode, and the second electrode A bioimpedance measurement apparatus comprising: an error detection unit that determines that there is a contact error between the electrode, the third electrode, and the fourth electrode. The bioimpedance measurement apparatus according to claim 3,
The error detection part
A sampling unit that samples the output signal of the differential amplifier circuit at a cycle shorter than the cycle of the alternating current and obtains it as sampling data;
A sampling data storage unit for temporarily storing sampling data acquired by the sampling unit;
A bioimpedance measuring apparatus, comprising: a distortion amount calculation unit that calculates the distortion amount using sampling data stored by the sampling data storage unit. The bioimpedance measurement apparatus according to claim 4,
The distortion amount calculation unit
A first sampling time and a first sampling voltage value corresponding to the maximum point of the output signal of the differential amplifier circuit are extracted from the sampling data, and correspond to the minimum point of the output signal of the differential amplifier circuit. Extracting a second sampling time and a second sampling voltage value, and further extracting a third sampling voltage value obtained at an intermediate time between the first sampling time and the second sampling time;
A bioimpedance measuring apparatus, wherein a deviation amount of the third sampling voltage value with respect to an average value of the first sampling voltage value and the second sampling voltage value is calculated as the distortion amount. The bioimpedance measurement apparatus according to claim 4,
The distortion amount calculation unit
A first sampling time and a first sampling voltage value corresponding to the maximum point of the output signal of the differential amplifier circuit are extracted from the sampling data, and correspond to the minimum point of the output signal of the differential amplifier circuit. Extracting a second sampling time and a second sampling voltage value, and further extracting a third sampling time giving an intermediate voltage between the first sampling voltage value and the second sampling voltage value;
A bioimpedance measuring apparatus, wherein a deviation amount of the third sampling time with respect to an average value of the first sampling time and the second sampling time is calculated as the distortion amount. The bioimpedance measurement apparatus according to claim 4,
The distortion amount calculation unit
A first sampling time and a first sampling voltage value corresponding to the maximum point of the output signal of the differential amplifier circuit are extracted from the sampling data, and correspond to the minimum point of the output signal of the differential amplifier circuit. Extract the second sampling time and the second sampling voltage value to be
The difference between the first sampling voltage value and the second sampling voltage value is an amplitude, has the same period as the period of the alternating current, and an average of the first sampling voltage value and the second sampling voltage value Set the sine wave whose value is a DC component,
A bioimpedance measuring apparatus, wherein a deviation amount of a sampling voltage value of the output signal of the differential amplifier circuit with respect to a voltage value of the sine wave is calculated as the distortion amount at each sampling time. The bioimpedance measurement apparatus according to claim 7,
The strain amount calculating unit averages the strain amount over a predetermined period including a plurality of sampling times, and uses the obtained average value of the strain amount as a second strain amount. .

Images