Thermocouple vs rtd online


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Explicación de los sensores de temperatura
1. RTD´s= Resitance Temperature D
2. Thermocuoples=Termocoples

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Thermocouple vs rtd online

  1. 1. RTD´s Thermocouples Recopila: Ing. Hugo Posada
  2. 2. Qué es un RTD? RTD stands for Resistance Temperature Detector. RTDs are sometimes referred to generally as resistance thermometers. The American Society for Testing and Materials (ASTM) has defined the term resistance thermometer as follows: Resistance thermometer, n. - a temperature-measuring device composed of a resistance thermometer element, internal connecting wires, a protective shell with or without means for mounting a connection head, or connecting wire or other fittings, or both. [Vol. 14.03, E 344 - 02 § 3.1 (2007).] An RTD is a temperature sensor which measures temperature using the principle that the resistance of a metal changes with temperature. In practice, an electrical current is transmitted through a piece of metal (the RTD element or resistor) located in proximity to the area where temperature is to be measured. The resistance value of the RTD element is then measured by an instrument. This resistance value is then correlated to temperature based upon the known resistance characteristics of the RTD element.
  3. 3. Cómo funciona un RTD? RTDs work on a basic correlation between metals and temperature. As the temperature of a metal increases, the metal's resistance to the flow of electricity increases. Similarly, as the temperature of the RTD resistance element increases, the electrical resistance, measured in ohms (Ω), increases. RTD elements are commonly specified according to their resistance in ohms at zero degrees Celsius (0° C). The most common RTD specification is 100 Ω, which means that at 0° C the RTD element should demonstrate 100 Ω of resistance. RTD elements are typically in one of three configurations: (1) a platinum or metal glass slurry film deposited or screened onto a small flat ceramic substrate known as "thin film" RTD elements, and (2) platinum or metal wire wound on a glass or ceramic bobbin and sealed with a coating of molten glass known as "wire wound" RTD elements. (3) A partially supported wound element which is a small coil of wire inserted into a hole in a ceramic insulator and attached along one side of that hole. Of the three RTD elements, the thin film is most rugged and has become increasingly more accurate over time.
  4. 4. Porqué un RTD tiene 2, 3, 4 alambres de conexion? A simple rule of thumb is that the more wires an RTD has the more accurate it is. The entire RTD assembly is not platinum. Among other issues, constructing an RTD in that manner would for most purposes be prohibitively expensive. As a result, only the small RTD element itself is made of platinum. Three wire RTDs are the most common specification for industrial applications. Three wire RTDs normally use a Wheatstone bridge measurement circuit to compensate for the lead wire resistance as shown below.
  5. 5. Como se conecta un RTD en un equipo de medición de temperatura?
  6. 6. Qué es un termocople? The American Society for Testing and Materials (ASTM) has defined the term thermocouple as follows: Thermocouple, n. - in thermometry, the sensor of a thermoelectric thermometer, consisting of electrically conducting circuit elements of two different thermoelectric characteristics joined at a junction. [Vol. 14.03, E 344 - 02 § 3.1 (2007).] A thermocouple occurs when any two different kinds of metals joined at a junction are exposed to a temperature gradient. When the two different metals are exposed to a temperature gradient they generate a very small electrical charge, commonly measured in millivolts, that correlates to the temperature to which the elements are exposed. This phenomenon is sometimes referred to as the Seebeck effect.
  7. 7. In the United States, different letter and color code designations are defined for each thermocouple type by the ANSI/ASTM E 230 standard. European standards are set by the IEC which uses different color code designation for thermocouples but largely sticks with the same letter designations
  8. 8. 1. Type J Thermocouple (Most Common): This thermocouple consists of an Iron and a Constantan leg and is perhaps the most common thermocouple in use in the United States. The bare Type J thermocouple may be used in vacuum, reducing, oxidizing and inert atmospheres. Heavier gauge is wire recommended for use above 1000 deg. F since the iron leg of this thermocouple oxidizes rapidly at high temperatures. 2. Type K Thermocouple (Most Common Real Hot): This thermocouple consists of a Chromel and an Alumel leg. This thermocouple is recommended for oxidizing or inert atmospheres up to 2300 deg. F. Cycling above and below 1800 deg. F is not recommended due to EMF alteration from hysteresis. This thermocouple is fairly accurate and stable at high temperatures. 3. Type N Thermocouple (A Newer, Better Type K): This thermocouple consists of a Nicrosil and a Nisil leg. This thermocouple is recommended for the same range as a Type K. It has better resistance to degradation due to temperature cycling, green rot and hysteresis than the Type K and is typically very cost competitive with the Type K. 4. Type T Thermocouple (Most Common Real Cold): This thermocouple consists of a Copper and a Constantan leg. It may be used in vacuum, oxidizing, reducing and inert atmospheres. It maintains good resistance to corrosion in most atmospheres and high stability at sub-zero temperatures. 5. Type E Thermocouple (Most Common Power Application): This thermocouple consists of one Chromel leg and one Constantan leg. This thermocouple is not subject to corrosion in most atmospheres. The Type E also has the highest EMF per degree of any standard thermocouple type. However, this thermocouple must be protected from sulfurous atmospheres. 6. Type B, R & S Thermocouples (Most Common Real, Real Hot): Platinum & Rhodium Thermocouples. Recommended for use in oxidizing or inert atmospheres. Reducing atmospheres may cause excessive grain growth and drift in calibration of these thermocouples. Types R & S may be used up to 1480 C. Type B may be used up to 1700 C. 7. Type C Thermocouple (For the Hottest of Environments): Tungsten and Rhenium thermocouple. Recommended for use in vacuum, high purity hydrogen or pure inert atmospheres. May be used at extremely high temperatures (2316 C). This thermocouple, however, is inherently brittle.
  9. 9. Como se conecta un TERMOPAR en un equipo de medición de temperatura?
  10. 10. REFERENCIAS.