 Welcome to this video, thermocouples. A thermocouple is an electrical temperature sensor that is capable of converting heat into voltage. The amount of voltage that is produced is proportional to the amount of heat to which it is exposed. Thermocouples are made of two dissimilar metals joined together. When exposed to heat, a small number of electrons drift from one metal to the other at the junction. The result is that a small voltage develops across the junction. Observe how this voltage develops. Watch as we place a thermometer into a container of hot liquid and take a measurement. Now we place a thermocouple in the hot liquid and record the voltage measurement. Use the table from the manufacturer of this J thermocouple to determine the temperature of the water. Does the temperature measured by the thermocouple match the temperature measured by the thermometer? No, it does not. The connection between the positive lead from the voltmeter, which is made of copper, and the iron wire of the thermocouple forms a second junction that produces a voltage. The voltage it produces is not the same as the voltage at the primary junction for two reasons. The secondary junction is connected by a terminal and not twisted together, and the secondary junction is exposed to the ambient air temperature, not the hot water. For this reason, a small voltage forms at the secondary junction and cancels some of the voltage at the primary junction. This situation will cause an inaccurate reading. One way to solve this problem is to control the voltage of the secondary junction. This is achieved by immersing the junction into ice water, that is, at 32 degrees Fahrenheit. At this temperature, the junction does not produce any voltage. This connection is referred to as the reference, or the cold junction. Take the voltage measurement of the thermocouple by immersing the reference junction into the ice water. Using the manufacturer's table, determine the temperature measured by the thermocouple. Now we'll check your understanding. Feel free to press pause if you need more time to review the questions. Question 1. Voltage readings of the thermocouple are taken to determine temperature measurements. Question 2. When the secondary junction is not immersed in ice water, the voltage it produces cancels some of the voltage produced by the primary junction. Question 3. Using the manufacturer's table, determine the temperature when the thermocouple produces 1.48 millivolts. The correct answer is 30 degrees Celsius. Congratulations! You've completed this activity, thermocouples.