Calibration of a Temperature Sensor

Introduction:

Thermometry is the measurement of the temperature of an object or system. Our skin has a sense of temperature, but it is not very reliable. After exposure to a given temperature for a sufficient amount of time our skin (or our brain) tends to have that temperature feel normal.

 Any physical property that varies consistently with temperature (which is almost ALL physical properties) can be used as a thermometer. It is desirable to have a nice, linear behavior of the thermometric property on the temperature. In many cases this is not possible, unless one is willing to change thermometers often.

In the upcoming labs we will be using conventional liquid-in-glass thermometers and electronic temperature sensors. Today we will confirm the inappropriateness of using our sense of temperature for quantitative (or even qualitative) measurements and investigate how to calibrate an uncalibrated electronic temperature sensor to make useful measurements.

 

Response of the Skin to Objects of Different Temperature

There will be three pans of water located in the lab. One will be a mixture of ice and water and its temperature will be about 32 0F or  0 0C. There will be another pan of water at a temperature much warmer than room temperature, perhaps 100 to 120 0F. The third pan will be at room temperature. Each group will have a liquid-in-glass thermometer so that you can accurately determine the true temperature of the pail.  Record the temperature of each pail gently using the thermometer as a stirring rod.  Then place one hand in the hot water and the other in the ice water for about 30 seconds (or as long as you can stand). Then quickly place both hands into the room temperature water. Pay careful attention to the temperature that each hand feels.  Comment on your observations.

 

Calibration of an Electronic Temperature Sensor

There are many kinds of thermometers.  Some are more familiar than others - liquid-in-glass being the most common type.  The LabPro that we used frequently last semester can be equipped with a sensor that measures changes in temperature - i.e., a temperature probe.  The probes can be calibrated directly in temperature, but today we will prefer to use the uncalibrated data to learn how the raw data is turned into a useful temperature value.

Experimental steps:

T = B + M*RD

where M is the slope of the line and B is the y-intercept.  Write the equation in your book with the appropriate numerical values for M and B (i.e. it should be something like T = 6.543 * RD +1.234 -- use your numbers).  Be sure to pay attention to the units as well as number itself.  Once you know M, you can use your data for the ice water to find B.