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. A bio signal measuring apparatus comprising;
a voltmeter;
a current source;
a plurality of electrodes capable of contacting a surface of an examinee and comprising a pair of a first current electrode and a second current electrode to which the current source applies current, a pair of a first voltage electrode and a second voltage electrode from which the voltmeter detects a voltage between the first voltage electrode and the second voltage electrode;
a first switch disposed between the first current electrode and the first voltage electrode;
a second switch disposed between the second current electrode and the second voltage electrode; and,
a processor configured to:
obtain a first impedance value of the examinee in a first mode in which the first switch and the second switch are in an open state;
obtain a second impedance value of the examinee in a second mode in which the first switch and the second switch are in a closed state; and
obtain bio impedance of the examinee by using the first impedance value, the second impedance value, an internal impedance value of the current source, and an input impedance value of an impedance measuring circuit as data for obtaining the bio impedance,
wherein, in the second mode, an internal impedance of the current source, an input impedance of the impedance measuring circuit, the current source and the voltmeter are parallel-connected to each other, one end of each of the internal impedance of the current source, the input impedance of the impedance measuring circuit, the current source and the voltmeter is electrically connected to both the first current electrode and the first voltage electrode in parallel, and another end of each of the internal impedance of the current source, the input impedance of the impedance measuring circuit, the electrically current source and the voltmeter is connected to both the second current electrode and the second voltage electrode in parallel.
2. The apparatus of claim 1 , wherein, in the first mode, 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.
3. The apparatus of claim 1 , wherein the processor is configured to obtain the bio impedance of the examinee 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.
4. The apparatus of claim 3 , wherein the processor is configured to obtain the bio impedance of the examinee 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 the input impedance value of the impedance measuring circuit, and Z s is the internal impedance of the current source.
5. The apparatus of claim 1 , 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.
6. The bio signal measuring apparatus of claim 5 , wherein the parallel impedance is smaller than the internal impedance of the current source.
7. The bio signal measuring apparatus of claim 1 , wherein contact impedance values between each of the first current electrode, the second current electrode, the first voltage electrode, and the second voltage electrode and the surface of the examinee have different impedance values, respectively.
8. 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.
9. The apparatus of claim 8 , 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.
10. The apparatus of claim 1 , wherein the bio signal measuring apparatus is a wearable device.
11. The apparatus of claim 1 , wherein at least one of the plurality of electrodes contacts a user's body when the user wears the bio signal measuring apparatus.