Temperature calibration system
AssigneeKing Nutronics Corporation
InventorsDaniel Y. Chang, Bradley C. Waldron, James M. Walthers, Sr.
Life of this patent
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Abstract
Method and apparatus for calibrating a temperature measuring device by operating a heat source at a preset temperature as determined by a temperature sensing resistor and a digitally calculated temperature which varies nonlinearly with the resistance of the resistor, and obtaining the coefficients for the calculation by operating the device at a preset temperature and comparing this temperature with that of a standard temperature measuring device.
Claims12
In an apparatus for providing a desired temperature for use in calibrating a temperature measuring device, the combination of:
- a heat source having a receptacle for receiving the temperature measuring device to be calibrated;
- means for measuring the temperature of said heat source to provide a measured temperature, said means including a temperature sensing resistor having a nonlinear relationship between the temperature and resistance of said resistor;
- means for setting in digital form a desired temperature for the heat source;
- control means for controlling electric power for connection to said heat source for controlling the temperature of said heat source;
- a bridge circuit having four arms and two pairs of terminals, with said temperature sensing resistor connected as one arm thereof and resistors of known resistance connected as the other arms thereof, with a known voltage connected across one pair of bridge terminals and providing a differential voltage at the other pair of bridge terminals, which differential sensing resistor;
- a converter for converting said differential voltage to a digital resistance number;
- a processor having said digital resistance number as an input for calculating the digital temperature of said temperature sensing resistor as a measure of the temperature of said heat source;
- said processor including means for comparing said digital temperature of said temperature sensing resistor and said digital desired temperature to provide a digital temperature error signal;
- and
- means for converting said digital temperature error signal to an analog signal as an input to said control means for controlling the electric power to said heat source;
- wherein said processor includes means for calculating said digital temperature of said temperature sensing resistor using known equations with three predetermined coefficients, and including
- a coefficient memory for said predetermined coefficients, and
- means for storing values for said coefficients in said memory, and
- wherein said known equations are the IPTS-68 equations.
In a method for providing a desired temperature for use in calibrating a temperature measuring device using an electrically energized heat source with temperature sensing resistor mounted therein, which resistor has a nonlinear relationship between its temperature and its resistance, the steps of:
- setting a desired temperature in digital form for the heat source;
- measuring the temperature of the heat source and providing a differential voltage which varies with the resistance of the temperature sensing resistor mounted in the heat source;
- converting the differential voltage to a digital resistance number;
- calculating the digital temperature of the temperature sensing resistor as a measure of the temperature of the heat source using the digital resistance number of the temperature sensing resistor as an input;
- comparing the digital temperature of the temperature sensing resistor and the digital desired temperature to provide a digital temperature error signal;
- converting the digital temperature error signal to an analog signal;
- controlling the electric power to the electrically energized heat source as a function of the analog signal to change the temperature of the heat source and reduce the magnitude of the error signal;
- and
- calculating the temperature of the temperature sensing nonlinear resistor using the IPTS equations:
- ##EQU3## where t.sub.68 is the temperature in degrees Celsius, corrected per IPTS-68,;
- t' is the temperature of the nonlinear resistor prior to IPTS-68 correction;
- M(t') is the IPTS-68 corrective, for temperature above zero degrees Celsius;
- R(t') is the resistance of the nonlinear resistor at the temperature t', prior to IPTS-68 correction;
- Ro is the ice-point resistance of the nonlinear resistor;
- alpha is the slope of the curve of resistance vs. temperature of the nonlinear resistor;
- and
- rho is the curvature of the slope.
Dependencies are inferred from the claim text.