what is the difference between a thermocouple and a thermopile

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Thermocouples can be connected in series to form a thermopile, where all the hot junctions are exposed to a higher and all the cold junctions to a lower temperature. When turned on, the pilot in a gas stove generates heat, which travels through a thermocouple. Thermocouples are a widely used type of temperature sensor. As the heat reaches the second junction of the thermocouple, it generates electrical voltage. The voltage of the electricity gives an accurate reading of a temperature between the ends of the device. By creating an account you agree to the Hunker, “Perspectives in Optoelectronics”; Sudhanshu Shekhar Jha, Virginia Tech Scholar Library: Thermopile, “A Complete Course in ISC Physics”; VP Bhatnagar. Thermopiles and thermocouples were invented in the 19th century. Thermocouples A thermocouple uses two metal wires to produce a voltage relative to the temperature present in the junction between them. Once the detector is pointed toward the object, heat flows from the object to the thermopile. A transducer consisting of two different metals welded together at each end; a voltage is produced that is proportional to the difference in temperature between the two junctions (one of which is normally held at a known temperature). When it rejoins, it creates electricity. Heat enters at one end, splits, travels down each wire separately, then rejoins. Moreover unlike thermocouple which is contact based temperature sensor, thermopile is … Gish has a Bachelor of Arts in art history from University of Massachusetts, Amherst. If the sensor has two lead wires, measure the resistance between the two leads. The thermocouple junction performs two essential roles. Also, while both devices detect radiation, thermopiles do so much more accurately, with a greater degree of sensitivity. The junction provides a heat conduction path that helps to maintain the ends of the two dissimilar wires at the same temperature (T j). If the appliance has a thermocouple, the problem may be a faulty thermocouple. The simple relationship between the temperature difference of the junctions and the measurement voltage is only correct if each wire is homogeneous (uniform in composition). The two top thermocouple junctions are at temperature T1 while the two bottom thermocouple junctions are at temperature T2. The main difference between Thermocouple and Thermopile is that the Thermocouple is a thermoelectric device and Thermopile is a device that converts thermal energy into electrical energy. A thermopile generates electricity from the heat of a pilot light. Most thermocouples cost 2.5 to 3 times less than RTDs and although RTD installation is cheaper than thermocouple installation, the savings in installation costs are not enough to tip the balance. Thermocouples have few benefits that makes them widely used. a THERMOCOUPLE is a device for measuring temperature in which two wires of different metals are joined. Thermopiles are used to measure temperature without having to contact the object being measured. The output of a thermopile is usually in the range of tens or hundreds of millivolts. A thermopile is an electronic device that converts thermal energy into electrical energy. In addition to measuring temperature difference and generating electricity, thermopiles can detect radiation within an environment. Please add askdifference.com to your ad blocking whitelist or disable your adblocking software. These devices appear in numerous applications, including appliances such as gas fireplaces and fireplace inserts. Thermocouples can be connected in series as thermocouple pairs with a junction located on either side of a thermal resistance layer. Furthermore, what does the pilot light do? Source; Wikipedia A thermopile is an electronic device that converts thermal energy into electrical energy. It produces higher voltage output compare to single thermocouple. When heat is applied to that hot junction, a small millivoltage is created. While both thermopiles and thermocouples give accurate temperature readings, thermopiles generate more electricity in doing so, making them more valuable in appliances that use them to generate electricity, not to read temperature. Thermopile sensor. Most obviously, thermopiles contain a series of interconnected thermocouples, meaning that technically speaking any device using thermopiles contains thermocouples. When used to measure temperatures, thermopiles and thermocouples must attach to a device that translates the voltage of the wire to a temperature reading. The thermocouple more or less acts like a sensor for gas flow and supplies gas to the pilot light through the gas valve. To help you simply understand, there’s only one main difference you’ll have to take note: A thermocouple is a sensor made of two pieces of metal used to measure temperature. There are many specialised kinds of thermocouples – they can combine different metals to measure various characteristics and temperature ranges, and produce specialised calibrations. The junction provides electrical continuity between the two legs of the thermocouple. The main difference between Thermocouple and Thermopile is that the Thermocouple is a thermoelectric device and Thermopile is a device that converts thermal energy into electrical energy. Seedbeck discovered that a pair of junctions between two wires made of different metals creates voltage equal to the temperature difference between the junctions. A thermocouple reliles on direct contact between its sensor tip and the object whose temperature is being measured. Thermopiles are a series of thermocouples and are used typically when the difference in heat is hard to measure. As thermocouples age in a process, their conductors can lose homogeneity due to chemical and metallurgical changes caused by extreme or prolonged exposure to high temperatures. Thermopiles do not respond to absolute temperature, but generate an output voltage proportional to a local temperature difference or temperature gradient. Sometimes you need to remove a grommet or RTV from around the wires to get them out. Three obvious differences exist between thermopiles and thermocouples. You should use a replacement with the same specifications as the original or your gas control may not function properly. The output voltage from the thermopile delta V is directly proportional to the difference in temperature or T1-T2, across the thermal resistance layer and the number of thermocouple junctions pairs. The thermopile, on the other hand, opens up the gas valve when the fireplaces are turned on. Adding more thermocouple pairs in series increases the magnitude of the voltage output. Thermocouples. Easy to Make Thermocouple Thermopile Make your own thermoelectric generator thermopile with paper clips and copper wire In our article What is a Peltier Cooler (1) we introduced the Seebeck Effect. Thermocouple - A sensor which measures temperature by the principle that the junction of two dissimilar metals will have a measurable difference in voltage output proportional to the difference in temperature between the measuring junction and the cold junction. The thermocouple, which operates as a safety device, turns the gas supply off when the pilot light goes out. a kind of thermometer consisting of two wires of different metals that are joined at both ends; one junction is at the temperature to be measured and the other is held at a fixed lower temperature; the current generated in the circuit is proportional to the temperature difference, a kind of thermometer for measuring heat radiation; consists of several thermocouple junctions in series. ... A thermopile is a number of thermocouples connected in series. Advantages & Disadvantages of Thermocouple. We need money to operate the site, and almost all of it comes from our online advertising. Because thermopiles generate more electricity than thermocouples, fireplaces with thermopiles can connect to thermostats for temperature control. The potential difference between the wires is a measure of the temperature of something they touch while the THERMOPILE is a set of thermocouples, either joined in series for increased voltage or in parallel for increased current, used to measure radiant energy or to convert … It is composed of alternate bars of antimony and bismuth, or any two metals having different capacities for the conduction of heat, connected with an astatic galvanometer, which is very sensibly affected by the electric current induced in the system of bars when exposed even to the feeblest degrees of heat. This one covers the thermopile and how it differs from the thermocouple. For instance, if a thermocouple generates two volts of electricity, and a thermopile contains four thermocouples, it generates two volts of electricity per thermocouple for a total of eight volts. When two different types of metal are joined together and there is a temperature difference between the two junctions, electrical current flows. Thermopile is composed of pair of thermocouples or more arranged in series or parallel. Thermocouples. The main limitation with thermocouples is accuracy; system errors of less than one degree Celsius (°C) can be difficult to achieve. Millivolt furnaces operate using a thermopile to power the system. An instrument of extreme sensibility, used to determine slight differences and degrees of heat. Commercial thermocouples are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. Thermocouples first appeared after the discovery of the thermoelectric effect by Thomas Johann Seedbeck in 1821. The advantages include the following. The output is the sum of the voltages across the individual junctions, giving larger voltage and power output. We don't have any banner, Flash, animation, obnoxious sound, or popup ad. Each additional thermocouple placed in a thermopile increases the device's ability to produce electricity. Most obviously, thermopiles contain a series of interconnected thermocouples, meaning that technically speaking any device using thermopiles contains thermocouples. In a thermopile detector, the "hot junctions" of the thermocouples face the incident IR radiation from the object, whereas the "cold junctions" are connected to a heat sink, which is usually a silica substrate. They are joined together at the tip (Hot Junction). Hunker may earn compensation through affiliate links in this story. The thermocouple is a device made up of two dissimilar metals. Luckily, despite the scientific complexity of thermopiles and thermocouples, you can understand their basic purpose through a brief description. Thermocouples and thermopiles use the principles of thermoelectricity to generate electricity by … The fireplace uses this voltage to open the gas valve, allowing gas to flow out and start a fire. While both thermopiles and thermocouples give accurate temperature readings, thermopiles generate more electricity in doing so, making them more valuable in appliances that use them to generate electricity, not to read temperature. This one covers the construction and output of the thermopile in gas appliances. Under load a thermopile should operate at no less than 190MV. Thermocouples operate by measuring the temperature differential from their junction point to the point in which the thermocouple output voltage is measured. The two top thermocouples are a connected junction are at temperature T1 while the two bottom thermocouple junction is at temperature T2. Understanding the differences between a thermopile and a thermocouple fireplace requires an understanding of the differences between these two devices. The output from the thermocouple pair will be a voltage that is directly proportional to the temperature difference across the thermal resistance layer and also to the heat flux through the thermal resistance layer. Thermocouples are widely used in science and industry. The process is also an example of the Peltier effect (electric current transferring heat energy) as the process transfers heat from the hot to the cold junctions. As nouns the difference between thermocouples and thermopile is that thermocouples is while thermopile is an electronic device that converts thermal energy into electrical energy usually constructed using a series-combination of thermocouples. Usually, you can loosen the retainer nut on the thermopile with a 7/16" open end wrench. 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