Temperature control system for cutaneous gas monitor

• US 4,805,122 A
• Filed: 01/25/1988
• Issued: 02/14/1989
• Est. Priority Date: 12/31/1986
• Status: Expired due to Term

• Current Assignee: Sensormedics Corporation (Becton, Dickinson & Co)
• Original Assignee: Sensormedics Corporation (Becton, Dickinson & Co)
• Inventors: Pawlowski, Michael, McDavid, Larry S., Foster, Stuart L., Stillman, Gerald T.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Dixon, Joseph L.
• Application Number:
  US07/148,115
• Time in Patent Office: 386 Days
• Field of Search: 364/153, 364/154, 364/183, 364/184, 364/415, 364/417, 364/506, 364/557, 364/580, 128/635, 128/736, 374/163, 123/179 B, 123/179 K, 204/403, 204/406, 204/408, 204/431
• US Class Current: 700/300
• CPC Class Codes: A61B 5/1491 Heated applicators
• CPC Class Codes: G05D 23/1917 using digital means
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor

Abstract

A temperature control system for an electrically heated cutaneous gas sensor. A heating element is provided with heating current by a closed loop temperature control circuit. The system includes a plurality of temperature monitoring circuits which are arranged to turn off the flow of heating current if the temperature of the sensor takes on an unacceptable value. The system also includes temperature setting circuitry for applying an increased temperature setpoint signal to the temperature control circuit, for a predetermined time, to reduce the time delay between the application of the sensor to the patient and the production of usable sensor data. Timing circuitry assures that the flow of heating current is not turned off in response to normal sensor temperature transients.

Claims

1. A cutaneous gas monitoring system comprising;

a sensor;

a first sensing means for generating a first output signal indicative of the actual temperature of the sensor;

a heating means for elevating the temperature of the sensor;

a control means for establishing a temperature setpoint signal variable between, at least, a first and a second temperature, and indicative of a desired temperature of the sensor, wherein the temperature setpoint signal is established at the second temperature for a predetermined length of time after the sensor is placed on a patient and the temperature setpoint signal is established at the first temperature after the elapse of the predetermined length of time, wherein the first temperature is lower than the second temperature, and for regulating the heating means in accordance with the difference between the output signal of the sensing means and the temperature setpoint signal;

means connected to the first sensing means which functions to reduce the temperature of the sensor after the first output signal exceeds a predetermined value.

2. The monitoring system of claim 1 wherein the means which functions to reduce the temperature of the sensor disables the heating means.

3. The monitoring system of claim 1 wherein the means which functions to reduce the temperature of the sensor reduces the temperature setpoint signal.

4. The monitoring system of claim 1 wherein the means which functions to reduce the temperature of the sensor is connected to a second sensing means for generating a second output signal indicative of the actual temperature of the sensor.

5. The monitoring system of claim 4 wherein the means which functions to reduce the temperature of the sensor further comprises circuits for carrying out a test, using the first and second output signals, for determining whether both sensing means are functioning properly.

6. The monitoring system of claim 4 wherein the means which functions to reduce the temperature of the sensor operates when the difference between the first and second output signals exceeds a predetermined amount.

7. The monitoring system of claim 4 wherein the means for reduucing the temperature of the sensor operates after the second output signal exceeds a predetermined amount.

8. The monitoring system of claim 1 wherein the control means comprises a programmable microprocessor that is programmed for establishing the temperature setpoint signal and regulating the heating means.

9. The monitoring system of claim 8 further comprising a failure detecting means which functions to reduce the temperature of the sensor when a program of the microprocessor fails to properly execute.

10. The monitoring system of claim 9 wherein the failure detection means includes resettable means which functions to reduce the temperature of the sensor unless the microprocessor periodically resets the resettable means.

11. The monitoring system of claim 1 further comprising an override means preventing the means which functions to reduce the temperature of the sensor from operating if the first output signal exceeds the predetermined value during a temperature transient.

12. The monitoring system of claim 11 wherein the temperature transient results from changing the temperature setpoint signal.

13. The monitoring system of claim 11 wherein the temperature transient results during the start-up of the monitoring system.

14. A cutaneous gas monitoring system for measuring a partial pressure of a constituent gas comprising a heating element, and a temperature sensing element for producing an output signal indicative of the actual temperature of a cutaneous gas sensor, and a temperature control means connected to the heating element and to the temperature sensing element for controlling the flow of current through the heating element in accordance with the difference between the output signal of the sensing element and a variable temperature setpoint signal, and a switching means connected to the heating element responsive to a disable signal for limiting the flow of current through the heating element, and a temperature setting means connected to the temperature control means which establishes the temperature setpoint signal at a first temperature when the sensor measures the partial pressure of the constituent gas and which establishes the temperature setpoint signal at a second temperature for a predetermined length of time prior to when the sensor measures the partial pressure of the constituent gas wherein the first temperature is lower than the second temperature, and a disabling means connected to the sensing element and to the switching means for establishing the disable signal after the output signal of the sensing element exceeds a predetermined value.

15. The monitoring system of claim 14 wherein the temperature setting means and the temperature control means comprise a programmable microprocessor that is programmed for establishing the temperature setpoint signal and controlling the flow of current through the heating element.