System and method for in vivo calibration of a sensor

• US 5,437,284 A
• Filed: 12/30/1993
• Issued: 08/01/1995
• Est. Priority Date: 12/30/1993
• Status: Expired due to Term

• Current Assignee: Camino Laboratories, Inc.
• Original Assignee: Camino Laboratories, Inc.
• Inventors: Trimble, Brett A.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): Noori, Max H.
• Application Number:
  US08/175,871
• Time in Patent Office: 579 Days
• Field of Search: 73/4 R, 73/1 B, 128/673
• US Class Current: 600/486
• CPC Class Codes: A61B 5/031 Intracranial pressure
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: G01L 27/005 Apparatus for calibrating pressure sensors
• CPC Class Codes: G01L 9/0039 using photoelectric means

Abstract

Calibration apparatus and method for calibrating a movable pressure sensor include the use of a stop device to establish a reference position outside the sensing movement range of a first sensor. While in vitro, a reference pressure is established by applying pressure to the sensor to move it against the stop surface with a controllable pressure source. This reference pressure is stored. During use when the sensor is in an unknown position, such as when in vivo, the controllable pressure source applies pressure to move the sensor against the stop surface and the pressure required to do so is measured. The measured pressure is compared to the reference pressure to determine the unknown pressure and the system is then recalibrated. An optical system may be used as a second sensor to determine the position of the first sensor. Inner and outer housings in which the first sensor and stop surface are mounted are moved in relation to each other and the optical sensor during assembly of the calibration system to accurately and independently calibrate the first and optical sensors.

Claims

1. A calibration system for calibrating a sensor system having a first sensor that moves within a range when sensing a physiological parameter, the sensor system also having a processing system that monitors the position of the first sensor and provides an output signal representative of the physiological parameter based on the monitored position of the first sensor, the calibration system comprising:

a stop device located so as to restrict the first sensor to a known position outside the sensing movement range when the sensor is engaged with the stop device;

a controllable force generator that selectively applies force to the first sensor to move it into contact with the stop device;

a force gauge that measures the force applied by the force generator and provides a measured force signal representative of the force applied by the force generator to move the first sensor into contact with the stop device; and

a memory having stored therein a reference force used to move the first sensor from a selected position at which the first sensor was subjected to a first force to the stop device;

wherein the processing system controls the force generator to apply force to the first sensor to move it from an unknown position resulting from an unknown force acting upon the first sensor to the stop device, receives the measured force, signal from the force gauge, retrieves the reference force, and determines the value of the unknown force based on comparing the reference force to the measured force.

2. The calibration system of claim 1 wherein:

the first sensor movement range comprises a maximum position at which the first sensor would be located should the physiological parameter reach a maximum predetermined level; and

the stop device is located outside the first sensor movement range and beyond the maximum position.

3. The calibration system of claim 2 wherein the force generator selectively applies a reduced pressure against the first sensor to urge it into contact with the stop device.

4. The calibration system of claim 3 wherein:

the first sensor is located in an enclosed area that surrounds one end of the first sensor;

a vent tube is coupled to the enclosed area; and

the reduced pressure is applied to the first sensor through the vent tube.

5. The calibration system of claim 2 wherein:

the first sensor is mounted in an outer housing, the outer housing having a first opening for transferring the physiological parameter to the first sensor, the outer housing having a second opening;

an inner housing is mounted in the second opening of the first housing at a selected position and provides the stop device and an access port through which the force is applied by the force generator to the first sensor;

wherein the inner housing and associated stop device are mounted opposite the first opening and beyond the maximum position.

6. The calibration system of claim 1 wherein the processing system additionally controls the force generator to incrementally apply force to move the first sensing element into contact with the stop device.

7. The calibration system of claim 1 further for calibrating a sensor system that additionally comprises a second sensor that determines the position of the first sensor in sensing the physiological parameter, the second sensor being responsive to the distance of the first sensor from the second sensor, the calibration system further comprising:

a first housing within which the first sensor is mounted; and

a second housing having the stop device;

wherein the first housing and second housing are movable in relation to each other along the direction of movement of the first sensor and are bonded to each other in a position to permit the sensing movement range of the first sensor and to locate the stop surface outside that movement range;

wherein the second housing is movable in relation to the second sensor so that the first sensor is locatable at a desired distance from the second sensor.

8. A method of calibrating a sensor system having a first sensor that moves within a range when sensing a physiological parameter, the sensor system also having a processing system that monitors the position of the first sensor and provides an output signal representative of the physiological parameter based on the monitored position of the first sensor, the method of calibrating comprising the steps of:

locating a stop device to restrict the first sensor to a known position outside the sensing movement range when the sensor is engaged with the stop device;

selectively applying force to the first sensor to move it into contact with the stop device;

measuring the force applied by the force generator and providing a measured force signal representative of the force applied by the force generator to move the first sensor into contact with the stop device;

storing in a memory a reference force used to move the first sensor from a selected position at which the first sensor was subjected to a first force to the stop device;

controlling the force generator to apply force to the first sensor to move it from an unknown position resulting from an unknown force acting upon the first sensor to the stop device;

retrieving the reference force from the memory; and

determining the value of the unknown force based on comparing the reference force to the measured force.

9. The calibration method of claim 8 wherein the first sensor movement range comprises a maximum position at which the first sensor would be located should the physiological parameter reach a maximum predetermined level and the step of locating the stop device comprises locating the stop device outside the first sensor movement range and beyond the maximum position.

10. The calibration method of claim 9 wherein the method is further for calibrating a sensor system that additionally comprises a second sensor that determines the position of the first sensor in sensing the physiological parameter, the second sensor being responsive to the distance of the first sensor from the second sensor, the calibration method further comprising the steps of:

locating the first sensor in a first housing;

locating the stop device in a second housing;

moving the first housing and second housing in relation to each other along the direction of movement of the first sensor to locate the stop surface outside that movement range and bonding the first and second housings to each other once that position has been obtained; and

moving the second housing in relation to the second sensor so that the first sensor is locatable at a desired distance from the second sensor.

11. The calibration method of claim 8 wherein the step of selectively applying force to the first sensor to move it into contact with the stop device comprises applying a reduced pressure against the first sensor to urge it into contact with the stop device.

12. The calibration method of claim 11 wherein the step of applying a reduced pressure comprises applying the pressure to the first sensor through a vent tube coupled to an enclosed area surrounding one end of the first sensor.

13. The calibration method of claim 8 wherein the step of selectively applying force to the first sensor to move it into contact with the stop device comprises the step of incrementally applying the force to move the first sensing element into contact with the stop device.

14. A calibration system for calibrating a sensor system having a first sensor that moves within a range when sensing a physiological pressure and a second sensor that determines the position of the first sensor, the second sensor providing a position signal representative of the position of the first sensor, the sensor system also having a processing system that monitors the position signal and provides an output signal representative of the physiological pressure based on the monitored position of the first sensor, wherein the first sensor movement range comprises a maximum position at which the first sensor would be located should the physiological parameter reach a maximum predetermined level, the calibration system comprising:

a stop device located so as to restrict the first sensor to a known position outside the sensing movement range when the sensor is engaged with the stop device, the stop device being located beyond the maximum position of the first sensor;

a controllable pressure generator that selectively applies pressure to the first sensor to move it into contact with the stop device;

a pressure gauge that measures the pressure applied by the pressure generator and provides a measured pressure signal representative of the pressure applied by the pressure generator to move the first sensor into contact with the stop device; and

a memory having stored therein a reference pressure used to move the first sensor from a selected position at which the first sensor was subjected to a first pressure to the stop device;

wherein the processing system controls the pressure generator to apply pressure to the first sensor to move it from an unknown position resulting from an unknown pressure acting upon the first sensor to the stop device, receives the measured pressure signal from the pressure gauge, retrieves the reference pressure, and determines the value of the unknown pressure based on comparing the reference pressure to the measured pressure.

15. The calibration system of claim 14 wherein the pressure generator selectively applies a reduced pressure against the first sensor to urge it into contact with the stop device.

16. The calibration system of claim 15 wherein:

the first sensor is located in an enclosed area that surrounds one end of the first sensor;

a vent tube is coupled to the enclosed area; and

the reduced pressure is applied to the first sensor through the vent tube.

17. The calibration system of claim 14 wherein:

the first sensor is mounted in an outer housing, the outer housing having a first opening for transferring the physiological pressure to the first sensor, the outer housing having a second opening;

an inner housing is mounted in the second opening of the first housing at a selected position and provides the stop device and an access port through which the pressure is applied by the pressure generator to the first sensor;

wherein the inner housing and associated stop device are mounted opposite the first opening and beyond the maximum position.

18. The calibration system of claim 14 wherein the processing system additionally controls the pressure generator m incrementally apply pressure to move the first sensing element into contact with the stop device.

19. The calibration system of claim 18 further comprising:

a first housing within which the first sensor is mounted; and

a second housing having the stop device;

wherein the first housing and second housing are movable in relation to each other along the direction of movement of the first sensor and are bonded to each other in a position to permit the sensing movement range of the first sensor and to locate the stop surface outside that movement range;

wherein the second housing is movable in relation to the second sensor so that the first sensor may be located at a desired distance from the second sensor.

20. A sensor mounting system for mounting a first sensor that moves within a range when sensing a physiological parameter and a second sensor that determines the position of the first sensor, the responses of both the first and second sensors being dependent upon their positioning at a particular location in respect to the parameter to be sensed, the mounting system comprising:

a first housing within which the first sensor is mounted;

a second housing within which a stop device located so as to restrict the first sensor to a known position outside its sensing movement range when the sensor is engaged with the stop device is mounted;

wherein the first housing and second housing are movable in relation to each other along the direction of movement of the first sensor to provide for the sensing movement range of the first sensor and to locate the stop surface outside that movement range so that the first sensor is located at the particular position;

wherein the second and first housings are movable in relation to the second sensor so that the first sensor is locatable at the particular position in respect to the first sensor.

21. The sensor mounting system of claim 20 wherein the first sensor comprises a movable device, the position of which depends upon the physiological parameter sensed;

the second sensor comprises an optical location system that uses light energy to locate the position of the first sensor;

wherein the first and second housing are adapted to be located in respect to each other to provide for the movement range of the first sensor and are further adapted to then be located in respect to the second sensor to locate the second sensor at the particular position frown the first sensor.

22. A method of mounting a plurality of sensors of a sensor system in relation to each other, the plurality comprising a first sensor that moves within a range when sensing a physiological parameter and a second sensor that determines the position of the first sensor, the responses of both the first and second sensors being dependent upon their positioning at a particular location in respect to the parameter to be sensed, the method comprising the steps of:

mounting the first sensor in a first housing;

mounting in a second housing a stop device located so as to restrict the first sensor to a known position outside its sensing movement range when the sensor is engaged with the stop device;

moving the first housing and second housing in relation to each other along the direction of movement of the first sensor to provide for the sensing movement range of the first sensor and locating the stop surface outside that movement range so that the first sensor is located at the particular position; and

moving the second and first housings in relation to the second sensor so that the first sensor is locatable at the particular position in respect to the first sensor.