Temperature measurement in R.F. locations

• US 5,161,892 A
• Filed: 08/30/1991
• Issued: 11/10/1992
• Est. Priority Date: 10/13/1987
• Status: Expired due to Term

• Current Assignee: Respiratory Support Products, Inc.
• Original Assignee: Respiratory Support Products, Inc.
• Inventors: Beran, Anthony V., Shigezawa, Gordon Y.
• Primary Examiner(s): YASICH, DANIEL
• Application Number:
  US07/753,035
• Time in Patent Office: 438 Days
• Field of Search: 374/181, 374/182, 374/184, 374/178, 374/134, 374/180, 333/213, 333/216, 307/117, 307/310, 328/128, 361/1
• US Class Current: 374/179
• CPC Class Codes: A61B 2018/00797 measured by multiple temperature sensors
• CPC Class Codes: A61B 2018/00815 measured by a thermistor
• CPC Class Codes: A61B 2018/00821 measured by a thermocouple
• CPC Class Codes: G01K 7/13 Circuits for cold-junction compensation

Abstract

Temperature measurement with thermocouples is made more accurate, and the cost of disposable thermocouples is reduced by locating the cold junction close to the hot junction, utilizing a thermistor in thermal communication with the cold junction in developing a compensating voltage which varies with temperature as does the voltage produced by the cold junction, and applying the compensating voltage to cancel the cold junction voltage. The presence of radio frequency fields in the region of the thermocouple is detected and utilization of the thermocouple voltage is interrupted in intervals when the interference is greater than some preselected intensity. Further, the thermocouple voltage information is utilized to simulate the resistance a thermistor would have at the temperature represented by the thermistor voltage information and that simulated resistance is applied to instrumentation designed to measure temperature with a thermistor.

Claims

1. The method of negating the effect of electromagnetic interference induced in the temperature sensing circuitry of a temperature measuring system further including a signal processor which receives temperature information from the sensing circuitry and transmits processed temperature information to a display, said electromagnetic interference having a magnitude associated therewith, which method comprises the steps of:

a) developing signals indicative of the magnitude of said interference; and

b) disabling transmission of processed temperature information to said display in intervals during which the magnitude of said interference exceeds some preselected value.

2. For measuring temperature at a selected site, said site having an associated electromagnetic field intensity thereabout, the apparatus comprising:

a thermocouple circuit means for sensing temperature at said site comprising a hot junction connected in series with a cold junction;

signal processing means connected to said thermocouple circuit means for providing periodic indications of said temperature;

detection means for detecting said electromagnetic field intensity and for providing a disabling signal when the magnitude of said electromagnetic field intensity exceeds a selected magnitude; and

disabling means responsive to said disabling signal for rendering the signal processing means ineffective to provide a temperature indication.

3. For measuring temperature at a selected site, said site having an associated radio frequency field intensity thereabout, the apparatus comprising:

temperature sensing means for sensing the temperature at said site;

signal processing means connected to said temperature sensing means for providing periodic indications of said temperature;

radio frequency detection means for detecting said radio frequency field intensity and for providing a disabling signal when the magnitude of said radio frequency field intensity exceeds a selected magnitude; and

disabling means responsive to said disabling signal for rendering the signal processing means ineffective to provide a temperature indication.

4. For measuring temperature at a selected site, said site having an associated electromagnetic field intensity thereabout, the apparatus comprising:

a thermocouple circuit means for sensing temperature at said site comprising a hot junction connected in series with a cold junction;

signal processing means connected to said thermocouple circuit means for providing periodic indications of said temperature;

detection means for detecting said electromagnetic field intensity and for providing a disabling signal when the magnitude of said electromagnetic field intensity exceeds a selected magnitude;

disabling means responsive to said disabling signal for rendering the signal processing means ineffective to provide a temperature indication;

said signal processing means comprising a means for developing digital information indicative of the potential produced at said hot junction, and wherein said disabling means further comprises means for storing said digital information and responsive to the presence or absence of said disabling signal to respectively utilize or not utilize said current digital information to provide said temperature indication;

compensating means comprising a thermistor disposed in thermal proximity to said cold junction for generating a compensating potential corresponding, within a predetermined range of temperatures, to the potential developed at the cold junction;

means for including the compensating potential in said thermocouple circuit means in opposition to the potential developed at the cold junction;

said signal processing means being further responsive to the potential across the thermocouple circuit means for producing a simulated resistance whose value is indicative of that temperature; and

indicating means responsive to the simulated resistance for providing indicating signals indicative of said temperature.

5. For measuring temperature at a selected site, said site having an associated radio frequency field intensity thereabout, the apparatus comprising:

a thermocouple circuit means for sensing temperature at said site comprising a hot junction connected in series with a cold junction;

signal processing means connected to said thermocouple circuit means for providing periodic indications of said temperature;

radio frequency detection means for detecting said radio frequency field intensity and for providing a disabling signal when the magnitude of said radio frequency field intensity exceeds a selected magnitude; and

disabling means responsive to said disabling signal for rendering the signal processing means ineffective to provide a temperature indication.

6. The invention defined in claim 5 in which said signal processing means comprises a means for developing digital information indicative of the potential produced at said hot junction, and wherein said disabling means further comprises means for storing said digital information and responsive to the presence or absence of said disabling signal to respectively utilize or not utilize said digital information to provide said temperature indication.

7. The invention defined in claim 5 wherein said cold junction develops a potential and which further comprises:

compensating means comprising a thermistor disposed in thermal proximity to said cold junction for generating a compensating potential corresponding, within a predetermined range of temperatures, to the potential developed at the cold junction; and

means for including the compensating potential in said thermocouple circuit means in opposition to the potential developed at the cold junction.

8. The invention defined in claim 5 wherein a potential is developed across said thermocouple circuit means and which further comprises:

signal processing means responsive to the potential across the thermocouple circuit means for producing a simulated resistance whose value is indicative of that temperature; and

indicating means responsive to the simulated resistance for providing indicating signals indicative of said temperature.

9. The invention defined in claim 8 wherein a potential is developed at said cold junction and which further comprises:

compensating means comprising a thermistor disposed in thermal proximity to said cold junction for generating a compensating potential corresponding, within a predetermined range of temperatures, to the potential developed at the cold junction; and

means for including the compensating potential in said thermocouple circuit means in opposition to the potential developed at the cold junction.