Method for temperature compensation in a combined pressure and temperature sensor

• US 6,409,677 B1
• Filed: 05/25/2000
• Issued: 06/25/2002
• Est. Priority Date: 05/27/1999
• Status: Expired due to Term

• Current Assignee: St. Jude Medical Coordination Center BVBA (Abbott Laboratories Incorporated)
• Original Assignee: Radi Medical Systems AB (Abbott Laboratories Incorporated)
• Inventors: Tulkki, Sauli
• Primary Examiner(s): Shaver, Kevin
• Assistant Examiner(s): WINGOOD, PAMELA LYNN
• Application Number:
  US09/577,663
• Time in Patent Office: 761 Days
• Field of Search: 600/486, 600/488, 600/549, 600/561, 600/587, 73/544.3, 73/614.6, 73/619.7
• US Class Current: 600/561
• CPC Class Codes: A61B 5/01 Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue clinical contact thermometers G01K13/20
• CPC Class Codes: A61B 5/02156 Calibration means
• CPC Class Codes: A61B 5/6851 Guide wires

Abstract

A method for temperature compensation is disclosed which comprises the excitation of sensors in a guide wire sensor assembly so as to produce two distinguishable signals. At least a component of at least one of the signals is representative of the cable resistance and can be used for compensation purposes. There is also provided an apparatus suitable for such measurements having temperature compensation circuitry. The compensation circuitry comprises circuitry for selectively and independently registering a resistance value for a passive resistor on the chip.

Claims

1. A method of selectively measuring at least one of pressure and temperature in vivo, comprising the steps of:

providing a pressure sensor having two piezoresistive elements, said piezoresistive elements being coupled to a control unit by cables having a temperature dependence affecting a signal obtained from said piezoresistive elements;

providing excitation to said sensor to yield two different signals therefrom, such that at least a component of at least one of said signals is representative of cable resistance; and

using said component representative of the cable resistance to compensate for the influence of said cable resistance on at least one of temperature and pressure signals.

2. The method according to claim 1, wherein the first piezoresistive element is part of one branch of a Wheatstone bridge, and the second piezoresistive element is part of another, branch of said Wheatstone bridge, and wherein the excitation comprise a first excitation of the entire bridge and a second excitation of only a branch of the bridge containing the first piezoresistive element.

3. The method according to claim 2, wherein the excitation is a DC voltage applied to the bridge.

4. The method according to claim 3, wherein the second excitation is carried out by switching off a branch containing the second piezoresistive element.

5. The method according to claim 4, wherein said second excitation is performed at a lower frequency than the first excitation.

6. The method according to claim 1, wherein the excitation comprises a composite excitation at two different frequencies.

7. The method according to claim 6, wherein said composite excitation comprises a DC voltage excitation and an AC voltage excitation.

8. The method according to claim 1, wherein the excitation voltage is up to 15 V.

9. The method according to claim 6, wherein an AC-component of a signal from the first piezoresistive element is obtained by high-pass filtering the signal before feeding it into an amplifier;

the output from said amplifier is then fed into a multiplexer and further to an A/D converter where the signal is converted into digital data;

said digital data is then read by a CPU/DSP which calculates a value of the signal as a pressure signal;

an AC-component of a signal from the second piezoresistive element is obtained by high-pass filtering the signal before feeding it into an amplifier, the output from said amplifier is then fed into said multiplexer and further to said A/D converter where the signal is converted into digital data;

said digital data is then read by the CPU/DSP which calculates a value as a temperature signal; and

wherein a DC-component of a signal from the second piezoresistive element is low-pass filtered, and the filtered signal is fed into an amplifier, the output from said amplifier being fed into said multiplexer and further to said A/D converter where the signal is converted into digital data, this digital data being read by the CPU/DSP.

10. The method according to claim 1, wherein the sensor is mounted on a guide wire.

11. The method according to claim 1, wherein the sensor is mounted on a catheter.

12. A control unit suitable for processing signals from a sensor and guide wire assembly adapted to selectively measure at least one of pressure and temperature in vivo, said guide wire assembly comprising a pressure sensor and electrical conductors coupling said pressure sensor to said control unit, said pressure sensor having two piezoresistive elements, said assembly comprising parasitic resistances in said electrical conductors coupling said pressure sensor to the control unit, the control unit comprising:

means for selective excitation of said pressure sensor so as to yield two different signals therefrom;

means for selective registering of a component of one of said signals generated in response to excitation of said pressure sensor, said component being representative of said parasitic resistances; and

means for compensating at least one of said different signals for influence of said parasitic resistances, by using said component representative of the parasitic resistances.

13. The control unit as claimed in claim 12, wherein the excitation means comprises a DC voltage source.

14. The control unit as claimed in claim 13, comprising a switch operable so as to enable cutting an excitation voltage to a piezoresistive element at a selected frequency.

15. The control unit as claimed in claim 14, further comprising a first and a second instrumental amplifier having inputs for receiving a pressure signal and a temperature signal respectively, and outputs delivering a processable out-signal, a multiplexer coupled to the outputs of said amplifiers, an A/D converter coupled to said multiplexer, and a control unit coupled to sequentially receive outputs from said A/D converter.

16. The control unit as claimed in claim 12, wherein the excitation means comprises a DC voltage source and an AC voltage source, whereby the DC and AC excitation voltages are superimposed on each other.

17. The control unit as claimed in claim 12, further comprising a first instrumental amplifier having high pass filter means coupled to its input, said input being coupled so as to receive a high frequency component of a pressure signal, a second instrumental amplifier having a low pass filter means coupled to its input, said input being coupled so as to receive a low frequency component of a temperature signal, and a third instrumental amplifier having a high pass filter means coupled to its input, said input being coupled so as to receive a high frequency component of said temperature signal and outputs delivering a processable out-signal, a multiplexer coupled to the outputs of said amplifiers, an A/D converter coupled to said multiplexer, and a control unit coupled to sequentially receive outputs from said A/D converter.

18. A system for measurement of at least one property inside a biological subject, the system comprising:

a sensor on an elongated member;

a cable connected to the sensor, the cable having a cable resistance; and

a control unit, connected to the cable, that provides excitation to the sensor and cable to yield a signal representative of the cable resistance and that compensates the measurement of the property for influence of the cable resistance.

19. A system as set forth in claim 18, wherein the control unit provides two different excitation modes at two different periods of time, one of the two modes yielding the signal representative of the cable resistance.

20. A system as set forth in claim 18, wherein the control unit provides two different excitation frequencies, one of the two frequencies yielding the signal representative of the cable resistance.

21. A system as set forth in claim 18, wherein the elongated member is a guide wire.

22. A system as set forth in claim 18, wherein the elongated member is a catheter.

23. A system as set forth in claim 18, wherein the sensor is a pressure sensor.

24. A system as set forth in claim 18, wherein the sensor is a temperature sensor.

25. A system as set forth in claim 18, wherein the sensor is a pressure and temperature sensor.

26. A system as set forth in claim 18, wherein at least part of the cable is insertable inside the subject.