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A J-type thermocouple for use at temperatures between 0 and 100 °C was calibrated at the steam point in a device called a hypsometer. A hypsometer creates a constant temperature environment at the saturation temperature of water, at the local barometric pressure. The steam-point temperature is strongly affected by barometric pressure variations. Atmospheric pressure on the day of this calibration was 30.1 in. Hg. The steam-point temperature as a function of barometric pressure may be expressed as
where pQ= 29.921 in. Hg. At the steam point, the output voltage produced by the thermocouple, referenced to 0 °C, is measured as 5.310 mV. Construct a calibration curve for this thermocouple by plotting the difference between the thermocouple reference table value and the measured value (Vref - Vmeas) versus temperature. What is this difference at 0 °C? Suggest a means for measuring temperatures between 0 and 100 °C using this calibration, and estimate the contribution to the total uncertainty.
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Theory and Design for Mechanical Measurements
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