What is A Thermocouple?
A thermocouple is a device consisting of two different conductors (usually metal alloys) that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and controland can also be used to convert a temperature gradient into electricity. They are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. In contrast to most other methods of temperature measurement, thermocouples are self powered and require no external form of excitation. The main limitation with thermocouples is accuracy and system errors of less than one degree Celsius (C) can be difficult to achieve. Any junction of dissimilar metals will produce an electric potential related to temperature. Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are used for different temperature ranges. Properties such as resistance to corrosion may also be important when choosing a type of thermocouple. Where the measurement point is far from the measuring instrument, the intermediate connection can be made by extension wires which are less costly than the materials used to make the sensor. Thermocouples are usually standardized against a reference temperature of 0 degrees Celsius; practical instruments use electronic methods of cold-junction compensation to adjust for varying temperature at the instrument terminals. Electronic instruments can also compensate for the varying characteristics of the thermocouple, and so improve the precision and accuracy of measurements. Thermocouples are widely used in science and industry; applications include temperature measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes.
Thermocouples are common devices used to measure temperatures for industrial as well as household applications where temperatures can reach up to thousands of degrees Celsius. At the junction of two dissimilar metals, the thermoelectric effect produces a small measurable voltage that depends on the temperature of the junction. Chances are that your furnace, hot water heater and oven have thermocouples to provide temperature feedback to these systems. Thermocouples are relatively inexpensive, rugged, easy to use, and can have wide temperature-sensing ranges.
1-Purchase a K type thermocouple online or from a hardware store. Use it for most applications, ranging from your fridge to your furnace. The junction of a K type thermocouple consists of chrome-nickel and aluminum-nickel alloys. It has a temperature range from minus-200 degrees to 1,350 degrees Celsius, with a sensitivity of about 41 microvolts per degree.
Tips & Warning
Instead of using a multimeter, use a data acquisition system to read temperature data directly to your computer. The instructions for this may vary depending on your data acquisition system, but most systems can directly have thermocouples as inputs. If not, it may be necessary to read the voltage from the thermocouple and convert it to a temperature. The conversion from voltage to temperature can be found from the manufacturer of the thermocouple. It will usually involve a high order polynomial fit, but it is easily done with a spreadsheet software. For better accuracy, use a thermocouple data acquisition system with electronic cold-junction compensation. The accuracy of a thermocouple is typically within about 1 degree Celsius.
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