Two wire oscillator system for determining body empedance

• US 20060111645A1
• Filed: 11/23/2005
• Published: 05/25/2006
• Est. Priority Date: 11/24/2004
• Status: Active Grant

• Current Assignee: Measurement Ltd (Measurement Ltd., Inc.)
• Original Assignee: Measurement Ltd (Measurement Ltd., Inc.)
• Inventors: Petrucelli, Steven
• Granted Patent: US 7,809,436 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body

Abstract

An apparatus for determining body impedance comprising: first and second electrodes suitable for being electrically coupled to the body; and a variable frequency relaxation oscillator coupled to the electrodes; wherein, the period of oscillation is indicative of the body impedance.

Claims

1. An apparatus for determining body impedance comprising:

first and second electrodes suitable for being electrically coupled to the body; and

a variable frequency relaxation oscillator coupled to the electrodes;

wherein, the period of oscillation is indicative of the body impedance.

2. The apparatus of claim 1, wherein the oscillator comprises at least one amplifier.

3. The apparatus of claim 2, wherein the electrodes at least partially define a negative feedback network for said amplifier.

4. The apparatus of claim 3, wherein the first of said electrodes is resistively coupled to an output terminal of said amplifier.

5. The apparatus of claim 4, wherein the second of said electrodes is coupled to common through at least one capacitor and shorted to an inverting input terminal of said amplifier.

6. The apparatus of claim 5, further comprising a positive feedback network comprising a resistor electrically coupled between said amplifier output terminal and a non-inverting input terminal of said amplifier.

7. The apparatus of claim 4, wherein when biased and coupled to the body, said at least one capacitor charges and discharges exponentially through said electrodes with respect to said amplifier non-inverting input terminal.

8. The apparatus of claim 1, further comprising at least one resistor coupled across said electrodes.

9. The apparatus of claim 8, wherein said at least one resistor is around at least two hundred kilo-ohms.

10. A method for calibrating an apparatus for determining body impedance having first and second electrodes being suitable for being electrically coupled to the body, comprising:

determining a first period of oscillation for the apparatus associated with an open circuit condition between the electrodes; and

determining a second period of oscillation for the apparatus associated with a short-circuit condition between the electrodes;

wherein, the first period of oscillation is indicative of a first calibration value, and the second period of oscillation in combination with a slope coefficient is indicative of a second calibration value.

11. The method of claim 10, wherein the slope coefficient is indicative of a calibration.

12. The method of claim 10, further comprising storing data indicative of the first period of oscillation.

13. A method for measuring an impedance of a body, comprising:

electrically coupling first and second electrodes to the body;

electrically biasing a variable frequency relaxation oscillator having both a negative feedback network comprising said electrodes, and a positive resistive feedback network; and

measuring the period oscillation of said variable frequency oscillator, wherein the measured period of oscillation is indicative of the impedance of the body.

14. The method of claim 13, wherein the measured period of oscillation is proportional to the impedance of the body.

15. The method of claim 13, wherein the oscillator comprises at least one operational amplifier.

16. The method of claim 15, wherein the first of said electrodes is resistively coupled to an output terminal of said operational amplifier.

17. The method of claim 16, wherein the second of said electrodes is coupled to common through at least one capacitor and shorted to an inverting input terminal of said operational amplifier.

18. The method of claim 17, wherein said at least one capacitor charges and discharges exponentially through said electrodes with respect to said operational amplifier non-inverting input terminal.