Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
2000-04-17
2002-04-09
Shaver, Kevin (Department: 3736)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
Reexamination Certificate
active
06370425
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a weighing instrument with body fat meter for measuring simultaneously a bioelectrical impedance between both feet of a person in standing position and a weight, and for calculating and estimating a body fat amount based on such physical features as a height, a sex, an age and the like which are inputted other than above measurements, and, in particular, relates to a weighing instrument with body fat meter which responds to variations in a contact impedance between an electrode for measuring impedance and a sole of foot as a measured body.
BACKGROUND ART
Body fat meter which utilizes the fact that the composition of a human body can be estimated by the use of an impedance between ends of human body which can be obtained by applying a feeble constant current to an end of a measured person's body and measuring a voltage drop between electrodes (The American Journal of Clinical Nutrition, 41(4) 810-817 1985 “Assessment of fat-free mass using bioelectrical impedance measurement of the human body”) was proposed (by U.S. Pat. No. 4,008,721, JP 5-49050C, JP 7-51242A, etc.) and the products based on these proposals have been introduced into market. Among them, the product according to JP 5-49050C is introduced into market as an instrument which allows to estimate body fat with absolute ease, that is, a weighing instrument with body fat meter, wherein a flat metal electrode for measuring a bioelectrical impedance is attached to a position on a top surface of a loading board of a weighing instrument with which soles of both feet of a measured person come in contact when he gets on the weighing instrument, whereby, among factors for estimating the body fat amount, an impedance between ends of human body and a weight which vary in every measurement can be measured simultaneously and can be taken into calculation formulas.
In a conventional body fat meter, at first, such physical data as a height, a sex, a weight and the like are inputted through such an input device as a key switch and the like and are stored in a memory, and then an impedance measuring device is driven by a controller to output a bioelectrical impedance in an analogue form, and then said analogue impedance is converted into digital value by an A/D converter to be taken into an arithmetic processor, which calculates a body fat amount from the digital value of the bioelectrical impedance and the physical data such as the height and the like stored in the memory, and outputs to an indicator. Since a weight, different from other physical data, changes easily, and thereby it should be inputted every time for a measurement, a weighing instrument is installed so as for a weight of a measured person to be measured every time when an impedance is measured in the weighing instrument with the body fat meter.
This weighing instrument with the body fat meter has an alternation switch between an analogue output of the impedance measuring device and said A/D converter, and another end of the alternation switch is connected to an analogue output of the weighing instrument, and a control terminal of the alternation switch is connected to said controller, wherein, at first, an output of the weighing instrument is inputted into the A/D converter through the alternation switch to convert a weight value of a measured person into a digital value and to store said digital value in a memory, and then the alternation switch is switched to input an output of the impedance measuring device into the A/D converter to convert a measured value of the impedance into a digital value, so that the A/D converter is shared by the weighing instrument and the impedance measuring device (FIG.
1
).
In addition, the bioelectrical impedance measuring device of said conventional weighing instrument with body fat meter employs four-terminal method in order to eliminate an influence of variation in a contact resistance between an electrode and a human body upon a measured value (FIGS.
2
and
3
).
Electrodes A
1
, A
2
, B
1
and B
2
are arranged so that said electrodes come to contact with tiptoes and heels of both feet of the measured person when he gets on the loading plate of an electronic weighing instrument for measuring the weight of the measured person, and current terminals of a constant-current regulated AC power source with known current value of iR in 50 kHz are connected to the electrodes A
1
and A
2
and measurement terminals of AC voltmeter are connected to the electrodes B
1
and B
2
. This system is designed so that little current would flow into the measurement terminals of the AC voltmeter.
A bioelectrical impedance is represented by ri, a contact impedance of the right tiptoe by rA
1
, a contact impedance of the left tiptoe by rA
2
, a contact impedance of the right heel by rB
1
, and a contact impedance of the left heel is represented by rB
2
.
A constant-current regulated alternating current iR flows from rA
1
through ri and rA
2
and returns to the current terminal without being leaked to rB
1
and rB
2
.
At that time, the voltage drops made by rA
1
, ri and rA
2
are shown as below respectively.
vA
1
=iR×rA
1
(1)
vi=iR×ri (2)
vA
2
=iR×rA
2
(3)
Since little current flows into each measurement terminal of the AC voltmeter, voltage drops made by rB
1
and rB
2
could be counted to be zero, that is, the effects caused by rB
1
and rB
2
could be negligible, so that vi can be directly observed by the AC voltmeter.
From the equation (2), the internal impedance ri is calculated as:
ri=vi/iR (4)
so that said impedance ri can be derived from the observed value vi because iR is a known value.
The constant-current regulated AC power source comprises a constant-voltage regulated AC power source, a resistor R
1
and an OP amplifier (FIG.
4
).
An output of the constant-voltage regulated AC power source is connected to an end of the resistor R
1
and another end of the resistor R
1
is connected to a negative terminal of the OP amplifier. To the negative terminal is connected said electrode A
1
, to an output terminal of the OP amplifier is connected said electrode A
2
, and a positive terminal of the OP amplifier is connected to GND (0V). The negative terminal of the OP amplifier has the same potential as the positive terminal does as far as the output terminal is not saturated, and no current flow in from the negative terminal into the OP amplifier. Accordingly, the current flowing into the resistor R
1
directly flows into the electrode A
1
through the human body, reaches to the electrode A
2
and is absorbed by the output terminal of the OP amplifier. When the output voltage of the constant-voltage regulated AC power source is v, the voltage between both ends of the resistor R
1
is v, so that:
ri=v/R
1
(5)
that is, the known constant-current can be obtained because v and R
1
are known values.
The AC voltmeter comprises a differential amplifier, a rectifier, a low pass filter and an A/D converter. At first, the voltage between the electrodes B
1
and B
2
is amplified into N-times thereof by the differential amplifier.
At that time, an output voltage of the differential amplifier v is represented as below.
v=N×Vi=N×iR×ri (6)
When this output is inputted into the half-wave rectifier, the rectifier outputs only a positive portions of the AC voltage. This output is transformed into DC by the low pass filter and inputted into the A/D converter and then the digital values proportional to the internal impedance ri is obtained.
By these procedure, the bioelectrical impedance free from the contact impedance of the feet can be measured.
In order to perform a precise measurement as much as possible, however, this system is designed generally on the assumption that the contact impedance is small to some degree and the system is used with bare feet. The contact impedance of a sole is generally less than 1 k&OHgr;, so that the maximum current value for m
McDermott & Will & Emery
Shaver Kevin
Szmal Brian
Tanita Corporation
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