Rtd (resistance temperature detector)
- 1. RTD(RESISTANCE TEMPERATURE DETECTOR) Belleza, Marc Elo Brasileño, Nelyn Mae
- 3. • also called a resistance thermometer as the temperature measurement will be a measure of the output resistance. • the temperature of an object increases or decreases, the resistance also increases or decreases proportionally.
- 4. WHEN TO USE RESISTANCE TEMPERATURE DETECTORS? RTD's should be used when: • When accuracy and stability are a requirement of the customer’s specification • When accuracy must extend over a wide temperature range • When area, rather than point sensing improves control • When a high degree of standardisation is desirable
- 5. COMMON COMPONENTS OF A RTD
- 8. 1. RTD platinum resistance element: This is the actual temperature sensing portion of the RTD. Elements range in length from 1/8" to 3". There are many options. The standard temperature coefficient is an alpha of .00385 and the standard resistance is 100 Ω at 0° C. 2. RTD Outside diameter: The most common outside diameter is ¼" in the US or 6mm (.236") for non-US applications. However, outside diameters range from .063" to .500" 3. RTD Process Connection: Process connection fittings include all standard fittings used with thermocouples (i.e. compression, welded, spring-loaded, etc.). 4. RTD Wire Configuration: RTDs are available in 2, 3 and 4 wire configuration. 3 wire configurations are the most common for industrial applications. Teflon and fiberglass are the standard wire insulation materials. Teflon is moisture resistant and can be used up to 400° F. Fiberglass can be used up to 1000° F. 5. RTD cold end termination: RTDs can terminate on the cold end with plugs, bare wires, terminal heads and any of the reference junctions common to thermocouples.
- 9. sensing element : - simple or double 100 Ohm platinum at 0°C, with 2, 3 or 4 wires protecting tube : - generally stainless steel - possibly with reduced tip thermic element : - fixed diameters 6, 7, 8 mm - replaceable thermic element for protecting sheaths > 9mm - metallic - pring loaded connecting head : - aluminium - screwed or lever lid - ceramic terminal block
- 12. SENSING ELEMENT
- 14. RTD TYPES RTD types are broadly classified according to the different sensing elements used. Platinum, Nickel and Copper are the most commonly used sensing elements.
- 15. •Platinum - best metal for process type RTD’s. - withstand oxidation and is effective over a range of –200 to + 850 degrees C. - used in unsuitable environments where it can reduce atmospheric metallic vapours and also catalizable vapours if the element is bare. -can be used in radioactive environments. In industrial applications, a PRT is known to measure temperatures as high as 1500 degree Fahrenheit or 650 degrees C. • Copper - The greatest strength of this metal is its low cost. -performs poorly in oxidizing atmospheres and has a low output - inability to perform in narrow measuring spans. -measure temperatures as high as 120 degrees C. • Nickel - good compromise between copper and platinum. -has a higher output and is slightly less expensive than platinum. - extremely nonlinear above 300 degrees C.
- 17. ELEMENT TYPES • There are three main categories of RTD sensors: thin film, wire-wound, and coiled elements. While these types are the ones most widely used in industry there are some places where other more exotic shapes are used, for example carbon resistors are used at ultra low temperatures (-173 °C to - 273 °C). a.Carbon resistor elements b. Strain free elements c. Thin film elements d. Wire-wound elements e. Coiled elements
- 18. Carbon resistor elements -are cheap and widely used. -have very reproducible results at low temperatures. -most reliable form at extremely low temperatures -do not suffer from significant strain gauge effects. Strain-free elements -use a wire coil minimally supported within a sealed housing filled with an inert gas. -sensors work up to 961.78 °C and are used in the SPRTs that define ITS-90. -consist of platinum wire loosely coiled over a support structure, so the element is free to expand and contract with temperature -very susceptible to shock and vibration, as the loops of platinum can sway back and forth, causing deformation.
- 19. Thin-film elements -have a sensing element that is formed by depositing a very thin layer of resistive material, normally platinum, on a ceramic substrate (plating) - coated with an epoxy or glass that helps protect the deposited film and also acts as a strain relief for the external lead wires -Disadvantages of this type are that they are not as stable as their wire-wound or coiled counterparts. -can only be used over a limited temperature range -elements work with temperatures to 300 °C (572 °F) without further packaging, but can operate up to 600 °C (1,112 °F) when suitably encapsulated in glass or ceramic. Special high-temperature RTD elements can be used up to 900 °C (1,652 °F) with the right encapsulation.
- 20. Wire-wound elements -can have greater accuracy, especially for wide temperature ranges -sensing wire is wrapped around an insulating mandrel or core. - core can be round or flat, but must be an electrical insulator. The coefficient of thermal expansion of the winding core material is matched to the sensing wire to minimize any mechanical strain. This strain on the element wire will result in a thermal measurement error. -sensing wire is connected to a larger wire, usually referred to as the element lead or wire. This wire is selected to be compatible with the sensing wire, so that the combination does not generate an emf that would distort the thermal measurement. -with temperatures to 660 °C.
- 21. Coiled elements - largely replaced wire-wound elements in industry - has a wire coil that can expand freely over temperature, held in place by some mechanical support, which lets the coil keep its shape -“strain free” design allows the sensing wire to expand and contract free of influence from other materials, while providing the durability necessary for industrial use - basis of the sensing element is a small coil of platinum sensing wire. This coil resembles a filament in an incandescent light bulb. -housing or mandrel is a hard fired ceramic oxide tube with equally spaced bores that run transverse to the axes. - elements work with temperatures to 850 °C.
- 22. WIRING CONFIGURATION 2 wire RTD’S • The least accurate of the 3 types because since there is no way of eliminating the lead wire resistance from the sensor measurement . • 2 wire RTD’S are mostly used with short wires or where close accuracy is not required.
- 23. 3 wire RTD’s • the most common configuration used in industrial applications where the third wire provides the method for removing the average lead wire resistance from the sensor measurement.
- 24. 4 wire RTD’S • Primarily used in laboratory where closed accuracy is required. • In a 4 wire RTD actual resistance of the lead wires can be determined and removed from the sensor measurement.
- 25. 2 Wire Configuration RTD with Compensating Loop • Similar to a 4wire configuration RTD except that a separate pair of wires is provided as a loop to provide compensation for lead resistance and ambient temperature changes in lead resistance.
- 26. ADVANTAGES AND DISADVANTAGES ADVANTAGES • Very high accuracy • Excellent stability and reproducibility • Ability to be matched to close tolerances for temperature difference measurements. • Ability to measure narrow spans • Suitability for remote measurement DISADVANTAGES • Susceptibility to mechanical damage • Need for lead wire resistance compensation • Susceptibility to self-heating error • Susceptibility to signal noise • Unsuitability for bare use in electrically conducting substance • Generally not repairable • Need for power supply
- 27. ADVANTAGES • Linear over wide operating range • High temperature operating range • Good stability at high temperature DISADVANTAGES • Low sensitivity • Higher cost than thermocouples • No point sensing • Affected by shock and vibration • Requires three or four-wire operation
- 29. APPLICATIONS OF RTD • Air conditioning and refrigeration servicing • Food Processing • Stoves and grills • Textile production • Plastics processing • Petrochemical processing • Micro electronics • Air, gas and liquid temperature measurement • Exhaust gas temperature measurement • Immersion sensors • Surface mounted sensors
- 30. TEMPERATURE VS RESISTANCE TABLE
- 32. TAPOS NA GUYS (hatag lang usb ang mapa copy)