Rtd and thermocouples


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a small ppt on RTD and thermocouple basics

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Rtd and thermocouples

  1. 1. By:Ashutosh Katti (T3814)Aditya Medhekar (T3827) Mechatronix seminar 15 April 2012 1
  2. 2. What is an RTD? RTD stands for Resistance Temperature Detector. The change in temperature is detected by the change in resistance of the wire. There are two types of RTD, viz. having positive and negative thermal coefficients of resistivity (resistance increases or decreases with the increase in temperature respectively). Mechatronix seminar 15 April 2012 2
  3. 3. • RTDs are used for temperature measurements by using them in bridge circuits.• The change in temperature causes considerable resistance change which gives a voltage drop in accordance with the thermal coefficient of resistance of the wire.• This voltage is further amplified and the temperature is read thus. This is how the RTDs are used in circuits assisting in automatic control and measurement with high accuracy. Mechatronix seminar 15 April 2012 3
  4. 4. Advantages Due to no fluid present absolute temperature is recorded. It is highly sensitive and gives accurate results. It has a good range of temperature measurement. It can thus measure from very low to very high temperature. Due to electrical output (resistance change) it can be used with PLCs and complete automation can be achieved. Mechatronix seminar 15 April 2012 4
  5. 5. Applications of RTD It is widely used in furnaces for automatic temperature measurement. Due to its compactness, it replaces conventional thermometers as well as thermocouples thus eliminating the use of lots of wires. Used in medical and chemical laboratories to detect very low temperatures (like dry ice and liquid nitrogen). Due to electrical output it is used wherever feedback system is required and corrective action is thus taken in an automated system. Mechatronix seminar 15 April 2012 5
  6. 6. What are thermocouples?• Thermocouples are metal couples which work on the Seebeck effect.• In this effect, any conductor is subjected to a thermal gradient, it will generate a voltage.• Measuring this voltage necessarily involves connecting another conductor to the "hot" end. This additional conductor will then also experience the temperature gradient, and develop a voltage of its own which will oppose the original. Mechatronix seminar 15 April 2012 6
  7. 7. Types of thermocouplesThere are about 4 to 5 types of thermocouples which are categorized based on sensitivity and range.• J and K type thermocouples are noted for their high sensitivity. These however, have a limited range. (about 41µV/˚C for K and 55µV/°C)• Platinum Types: The B, S, T and R type of thermocouples are less sensitive (about 10µV/˚C) but they have a very significant advantage of high range. They can measure large temperatures and are usually used in furnaces. Mechatronix seminar 15 April 2012 7
  8. 8. Mechatronix seminar 15 April 2012 8
  9. 9. Thermocouple sensors• Sensitivity: It is the voltage or emf produced per degree Celsius rise or fall in temperature at the junction.• Construction: Simply welded or twisted between 2 metals.• Range: Thermocouples have the greatest range in all types of temperature measurement instrument domains. Mechatronix seminar 15 April 2012 9
  10. 10. • Time Response: It is the time required by the thermocouple to reach thermal equilibrium with the surrounding. Industrial TC using thick wire have lower response of about 20s however, TCs of small gauge wires have response time of about 20ms.• Signal conditioning: the output voltage from the thermocouples is very small usually less then 50 mV. Thus considerable amplification is required so as to be used for practical applications Mechatronix seminar 15 April 2012 10
  11. 11. RTD and Thermocouple Calibration SetupRTD TC Temperature indicator ON/OFF controller OVEN 230V AC 50 Hz Switch Mechatronix seminar 15 April 2012 11
  12. 12. Mechatronix seminar 15 April 2012 12