Impedance determination

Abstract

Apparatus for use in performing impedance measurements on a subject. The apparatus includes a processing system for causing a first signal to be applied to the subject, determining an indication of a second signal measured across the subject, using the indication of the second signal to determine any imbalance and if an imbalance exists, determining a modified first signal in accordance with the imbalance and causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.

What is claimed is: 
     
         1 ) An apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes a number of electrode systems, and wherein each electrode system includes:
 a first substrate having a signal generator and sensor mounted thereon, the signal generator being for applying a first signal to the subject and the sensor for sensing a second signal across the subject; and
 a second substrate having at least two conductive pads mounted thereon, the conductive pads forming first and second electrodes for coupling the signal generator and the sensor to a subject in use. 
   
     
     
         2 ) The apparatus of  claim 1 , wherein the electrode system includes a capacitive cancelling circuit for cancelling capacitive coupling between the drive and sense electrodes. 
     
     
         3 ) The apparatus of  claim 2 , wherein the capacitive cancelling circuit includes an inverting amplifier for coupling a signal generator output to a sensor input. 
     
     
         4 ) The apparatus of  claim 3 , wherein the inverting amplifier applies a capacitance cancelling signal to the sensor input to thereby cancel any effective capacitance between the drive electrode and the sense electrode. 
     
     
         5 ) The apparatus of  claim 3 , wherein an inverting amplifier output is coupled to the sensor input via at least one of:
 a resistor;   a capacitor; and   an inductor.   
     
     
         6 ) The apparatus of  claim 5 , wherein at least one of a resistor and capacitor are adjustable, thereby allowing a capacitance cancelling signal applied to the sensor input to be controlled. 
     
     
         7 ) The apparatus of  claim 1 , wherein the electrode system includes an input capacitance cancelling circuit for cancelling an effective input capacitance at a sensor input. 
     
     
         8 ) The apparatus of  claim 7 , wherein the electrode system includes a feedback loop for connecting a sensor output to the sensor input. 
     
     
         9 ) The apparatus of  claim 8 , wherein the feedback loop includes at least one of:
 a resistor;   a capacitor; and   an inductor.   
     
     
         10 ) The apparatus of  claim 9 , wherein at least one of a resistor and capacitor are adjustable, thereby allowing a current flow from the sensor output to the sensor input to be controlled. 
     
     
         11 ) The apparatus of  claim 9 , wherein the feedback loop applies an input capacitance cancelling signal to the sensor input to thereby cancel any effective capacitance at the sensor input. 
     
     
         12 ) An apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes:
 a number of electrode systems, and wherein each electrode system includes a signal generator and sensor, the signal generator being for applying a first signal to the subject and the sensor being for sensing a second signal across the subject; and   at number of leads for connecting the measuring device to the electrode systems, each lead including:
 at least two connections for connecting the measuring device and the signal generator, and the measuring device and the sensor; and 
 a shield for each of the at least two connections, the shields being electrically connected, and connected to a reference voltage in each of the measuring device and the electrode system. 
   
     
     
         13 ) The apparatus of  claim 12 , wherein the apparatus includes:
 at least two electrode systems;   a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and   at least two leads for connecting the measuring device to the electrode systems.   
     
     
         14 ) The apparatus of  claim 13 , wherein the leads are arranged in use to at least one of:
 extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and   minimize the lead length.   
     
     
         15 ) An apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes:
 at least two electrode systems, and wherein each electrode system includes a signal generator and sensor, the signal generator being for applying a first signal to the subject and the sensor being for sensing a second signal across the subject; and   a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and   at least two leads for connecting the measuring device to the electrode systems, the leads being arranged to at least one of:
 extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and 
 minimize the lead length. 
   
     
     
         16 ) The apparatus of  claim 15 , wherein the apparatus includes:
 four electrode systems; and   four leads extending from the measuring device in four different directions.   
     
     
         17 ) The apparatus of  claim 15 , wherein each lead includes:
 a first cable for coupling the measuring device to the signal generator to thereby allow the measuring device to control the signal generator to apply a first signal to the subject;   a second cable for coupling the measuring device to the signal generator to thereby allow the measuring device to determine a parameter relating to the first signal applied to the subject; and   a third cable for coupling the measuring device to the sensor generator to thereby allow the measuring device to determine a voltage measured at the subject.   
     
     
         18 ) The apparatus of  claim 15 , wherein the electrode system includes:
 a first substrate having the signal generator and sensor mounted thereon; and,   a second substrate having at least two conductive pads mounted thereon, the conductive pads being for coupling the signal generator and the sensor to a subject in use.