Apparatus and method of measuring bio signal
A method of measuring a bio signal using a bio signal measuring apparatus includes: positioning electrodes included as part of the bio signal measuring apparatus to contact a surface of an examinee; switching an impedance measurer included as part of the bio signal measuring apparatus and including a voltmeter and a current source; measuring a first impedance value of the examinee while operating the impedance measurer according to a first mode; switching the impedance measurer to a second mode; measuring a second impedance value of the examinee while operating the impedance measurer according to a second mode; and obtaining bio impedance of the examinee based on the first and second impedance values and an internal impedance of the current source.
1. An apparatus configured to measure a bio signal, the apparatus comprising:
a plurality of electrodes comprising a first current electrode, a second current electrode, a first voltage electrode and a second voltage electrode;
an impedance measurer comprising a voltmeter and a current source, the current source inducing an internal impedance;
a first switch configured to switch between an open state and a closed state, and short-circuit the first current electrode and the first voltage electrode in the closed state;
a second switch configured to switch between the open state and the closed state, and short-circuit the second current electrode and the second voltage electrode in the closed state;
a third switch that is disposed between the voltmeter and the first voltage electrode; and
a processor configured to:
obtain a first impedance value in a first mode in which the first switch and the second switch are in the open state;
obtain a second impedance value in a second mode in which the first switch and the second switch are in the closed state;
obtain a third impedance value in a third mode in which the first switch is in the closed state and the second and the third switches are in the open state so that the current source is connected between the first current electrode and the second current electrode, the voltmeter is connected between the first current electrode and the second voltage electrode, and the first voltage electrode is electrically disconnected from the current source; and
obtain bio impedance of an examinee based on the first, second, and third impedance values and the internal impedance of the current source.
2. The apparatus of claim 1 , wherein the current source is connected between the first current electrode and the second current electrode, and the voltmeter is connected between the first voltage electrode and the second voltage electrode, according to the first mode.
3. The apparatus of claim 1 , wherein a first common terminal of the current source and the voltmeter is connected to the first current electrode and the first voltage electrode, and a second common terminal of the current source and the voltmeter is connected to the second current electrode and the second voltage electrode, according to the second mode.
4. The apparatus of claim 1 , wherein the processor is configured to obtain the bio impedance by compensating for an effect of contact impedance between the plurality of electrodes and the examinee in the first and second impedance values based on the internal impedance of the current source.
5. The apparatus of claim 4 , wherein the processor is configured to obtain the bio impedance by using Equation 1:
Z
m
=
Z
4
P
(
β
+
Z
i
)
(
β
+
Z
S
)
Z
4
P
(
2
β
+
Z
i
+
Z
S
)
+
Z
i
Z
S
Equation
1
where β is defined by Equation 2,
β
=
2
1
Z
2
P
-
1
Z
i
-
1
Z
S
Equation
2
where Z 4P is the first impedance value, Z 2P is the second impedance value, Z i is an input impedance value of the impedance measurer, and Z s is the internal impedance of the current source.
6. The apparatus of claim 1 , wherein the impedance measurer further comprises:
a current source parallel impedance that is parallel-connected to the current source and which changes an effective value of the internal impedance of the current source.
7. The apparatus of claim 6 , wherein the current source parallel impedance has an impedance value that is less than the internal impedance of the current source.
8. The apparatus of claim 2 , wherein contact impedance values between the plurality of electrodes and the examinee have different impedance values, respectively.
9. The apparatus of claim 8 , wherein, when the first switch and the second switch are in the open state, the current source is connected between the first current electrode and the second current electrode, the voltmeter is connected between the first voltage electrode and the second voltage electrode, and the first voltage electrode is electrically disconnected from the current source.
10. The apparatus of claim 1 , further comprising a fourth switch that, is disposed between the voltmeter and the second voltage electrode,
wherein, the impedance measurer operates according to a fourth mode, the first and the fourth switches are in the open state and the second and the third switches are in the closed state so that the current source is connected between the first current electrode and the second current electrode, the voltmeter is connected between the first voltage electrode and the second current electrode, and the second voltage electrode is electrically disconnected from the current source.
11. The apparatus of claim 10 , further comprising a fifth switch that is disposed between the current source and the second current electrode,
wherein, the impedance measurer operates according to a fifth mode, the first and the fifth switches are in the open state and the second, the third, and the fourth switches are in the closed state so that the current source is connected between the first current electrode and the second voltage electrode, the voltmeter is connected between the first voltage electrode and the second voltage electrode, and the second current electrode is electrically disconnected from the current source.
12. The apparatus of claim 11 , wherein the processor is configured to obtain the bio impedance by compensating for an effect of the contact impedance between the first, second, third and fourth electrodes and the examinee in the first, second, third, fourth and fifth impedance values.
13. The apparatus of claim 1 , further comprising:
a display configured to output bio information of the examinee based on the bio impedance of the examinee.
14. The apparatus of claim 13 , wherein the bio information of the examinee comprises at least one of a body fat amount of the examinee, a basal metabolic amount of the examinee, a skeletal muscle amount of the examinee, a blood flow amount of the examinee, a breathing rate of the examinee, a heart rate of the examinee, and heart rate variation of the examinee.