Electrochemical measurement system having interference reduction circuit

Claim 1

Apparatus for measuring a predetermined parameter of an electrically-conductive fluid located in a tube and used in an environment where an undesired electrical current can be conducted by the fluid from a noise source at one end of the tube, the apparatus comprising: a reference electrode and a sensor electrode adapted to be attached to a tube at spaced-apart locations, contacting an electrically-conductive fluid in the tube; signal amplifier means for amplifying a voltage between the reference electrode and the sensor electrode and for providing a corresponding amplified signal; first and second noise-reduction electrodes adapted to be attached to the tube at spaced-apart locations, contacting the electrically conductive fluid in the tube, such that the reference and sensor electrodes are located between the first and second noise-reduction electrodes; and a noise reduction amplifier having an input terminal with a high impedance and an output terminal with a low impedance, the noise-reduction amplifier means being connected between the first and second noise-reduction electrodes, with its input terminal connected to the noise-reduction electrode furthest from the noise source and with its output terminal connected to the noise-reduction electrode closest to the noise source, such that any electrical current originating at the noise source bypasses the portion of the electrically-conductive fluid located in the tube between the reference and sensor electrodes by flowing instead through the noise reduction amplifier, whereby the amplified signal produced by the signal amplifier means is substantially unaffected by that electrical current.

Claim 14

A method for measuring a predetermined parameter of blood drawn from a patient into an intravenous tube, the method comprising steps of: providing an electrode and infusion tube assembly having a reference electrode and a sensor electrode located at spaced apart locations, the sensor electrode being sensitive to a particular parameter of blood; arranging the electrode and infusion tube assembly such that blood can be drawn from a patient into contact with one or both of the reference and sensor electrodes, wherein a potential develops between the two electrodes that is indicative of the predetermined parameter of the blood, and wherein electrical current interference originating at the patient can be conducted along the infusion tube by the blood contained in the tube; and connecting a noise-reduction amplifier between two noise-reduction electrodes located on opposite sides of the reference and sensor electrodes, wherein the amplifier has a high-impedance input terminal connected to the noise reduction electrode located furthest from the patient and a low-impedance output terminal connected to the noise reduction electrode closest to the patient, such that any electrical current interference originating at the patient bypasses the reference and sensor electrodes by flowing instead through the noise-reduction amplifier, whereby the potential developed between the reference and sensor electrodes is substantially unaffected by that electrical current.

Claim 15

A method for measuring a predetermined parameter of blood drawn from a patient into an intravenous tube, the method comprising steps of: providing an electrode and infusion tube assembly having a reference electrode and a sensor electrode located at spaced apart locations, the sensor electrode being sensitive to a particular parameter of blood; arranging the electrode and infusion tube assembly such that blood can be drawn from a patient into contact with one or both of the reference and sensor electrodes, wherein a potential develops between the two electrodes that is indicative of the predetermined parameter of the blood, and wherein electrical current interference originating at the patient can be conducted along the infusion tube by the blood contained in the tube; and connecting a noise-reduction amplifier between two noise-reduction electrodes located on opposite sides of the reference and sensor electrodes, wherein the amplifier has a high-impedance input terminal connected to the noise reduction electrode located furthest from the patient and a low-impedance output terminal connected to the noise reduction electrode closest to the patient, such that any electrical current interference originating at the patient bypasses the reference and sensor electrodes by flowing instead through the noise-reduction amplifier, whereby the potential developed between the reference and sensor electrodes is substantially unaffected by that electrical current.