LAB_10 - Temperature Transducers

LAB_10 - Temperature Transducers - Lab 10 Temperature...

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Lab 10 115 Temperature Transducers Summary The ability to make accurate measurements of temperature, temperature change and heat flow is essential in a modern industrial society. The operation of many devices is dependent on temperature. The measurement of temperature can be accomplished by using a variety of devices called temperature trans- ducers. These devices transform a change of temperature (input) into an output which is a change in another physical parameter such as voltage. In this experiment we will study three types of temperature transducers - thermometers, thermocouples, and thermistors. Thermometers are an example of complete measurement systems in that they have an output or read-out stage built into the same structure as the input or transducer stage. We will compare the range, sensitivity and dynamic response of each of these temperature trans- ducers. These characteristics plus others such as size, ruggedness and cost, are weighed to determine which transducer is most suitable for a given engineering application. Educational Objectives After performing this experiment, students should be able to: 1. Measure temperature using a thermistor, thermocouple and thermometer. 2. Make simple measurements of their range, sensitivity and dynamic response. 3. Prepare simple calibration curves for these devices. Background Information By definition, a transducer senses at its input a physical quantity called a measurand and trans- forms it into another physical quantity at its output. Most temperature measuring devices do not directly measure temperature, but instead measure the change in some other physical property. Some of these physical properties include: i. changes in volume or pressure in a gas, ii. changes of volume or length in liquids and solids iii. changes in electrical resistance of conductors or semiconductors iv. changes in voltage or light emitted by semiconducting devices v. changes in the spectrum of electromagnetic radiation emitted by various materials “Facts which at first seem improbable will even in scant explanation, drop the cloak which has hidden them and stand forth in naked and simple beauty.” - Galileo Galilei
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Lab 10 116 The response of transducers may be linear or nonlinear. In the case of linear temperature transduc- ers, the temperature difference is proportional to the change in the output. This is important, in that such devices are simple and easy to use. Nonlinear devices do not have this proportionality between tempera- ture difference and output and may require complicated calibration equations, tables or graphs to obtain the temperature. A certain amount of time is always required for any transducer to respond to the changes in its environment. In this experiment the response time of the device is defined as the time required for a sys- tem parameter to attain a value within 10% of the final value. For rapidly changing temperature applica- tions this becomes a critical consideration in determining the best device for a particular measurement.
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This note was uploaded on 12/16/2011 for the course ENGR 102 taught by Professor Cattell during the Fall '10 term at Community College of Philadelphia.

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LAB_10 - Temperature Transducers - Lab 10 Temperature...

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