do the instruments RTD(resistance temperature detector) and thermocouple work on same principle?

Question

What makes them different means where a RTD is used and where a thermocouple???

Answer 1

*No, RTD(resistance temperature detector) and thermocouple does not work on same principle.

#An RTD sensing element consists of a wire coil or deposited film of pure metal. The element's resistance increases with temperature in a known and repeatable manner. RTD's exhibit excellent accuracy over a wide temperature range and represent the fastest growing segment among industrial temperature sensors. Their advantages include:

Temperature range: -260 to 850°C (-436 to 1582°F)
Repeatability and stability: The platinum resistance thermometer is the primary interpolation instrument used by the National Institute of Standards and Technology(NIST)from -260 to 962°C. Laboratory models stable within 0.0025°C are available. Even ordinary RTD's typically drift less than 0.1°C/year.
Sensitivity: The voltage drop across an RTD provides a much larger output than a thermocouple.
Linearity: Platinum and copper RTD’s produce a more linear response than thermocouples or thermistors. RTD non-linearities can be corrected through proper design of resistive bridge networks.
Low cost system: RTD's use ordinary copper extension leads and require no cold junction compensation
Standardization: Manufacturers offer RTD’s to industry standard curves, most commonly 100Ω platinum to IEC 751.
Thermocouples:
# A thermocouple consists of two wires of dissimilar metals welded together into a junction. At the other end of the signal wires, usually as part of the input instrument, is another junction called the reference junction. Heating the sensing junction generates a thermoelectric potential (emf) proportional to the temperature difference between the two junctions. This millivolt-level emf, when compensated for the known temperature of the reference junction, indicates the temperature at the sensing tip. Published millivolt tables assume the reference junction is at 0°C. Thermocouples are simple and familiar. Designing them into systems however is complicated by the need for special extension wires and reference junction compensation.
*Thermocouples advantages include:

Extremely high temperature capability: Thermocouples with precious metal junctions may be rated as high as 1800°C(3272°F).
Ruggedness: The inherent simplicity of thermocouples makes them resistant to shock and vibration.
Small size/fast response: A fine-wire thermocouple junction takes up little space and has low mass, making it suitable for point sensing and fast response. Note, however, that many Minco RTD’s have time constants faster than equivalent thermocouples.
http://www.microdaq.com/accessories/choosing.php
http://en.wikipedia.org/wiki/Resistance_temperature_detector
http://en.wikipedia.org/wiki/Thermocouple

Answer 2

No, they do not.

RTD's operate on the principle that the electrical resistance of a conductor or semiconductor (usually Platinum) varies with temperature. The resistance across the RTD is measured, indicating the temperature.

Thermocouples operate on the principle that when two dissimilar conductors (metals) are in contact with eachother (a junction), they create an electromotive force (emf) that is related to the temperature of the junction. The magnitude of the emf is indicative of the temperature. For more thermocouple reference, look up these terms: Seebeck effect, Peltier effect and Thomson effect.

The specific application of either of these devices could be just about anything. Measurement uncertainty for an RTD can be as low as +/- 0.005 degrees Celcius. A thermocouple, at best, would yield a measurement uncertainty of +/- 0.1 to +/- 1.0 degrees Celcius. So if you need a really accurate and precise measurement, don't use a thermocouple.

Answer 3

No, the principle is not the same. An RTD is a component who's resistance changes dramatically over a certain temperature range. A thermocouple is based on a bimetallic junction, which will output a specific volt per degree, genmerally in the low millivolts range.

RTD's are easier and cheaper to incorporate into a circuit, since all you need do is supply a precision voltage to it. The output current will then be your indication of the temperature. For a thermocouple, you need to do a precision voltage measurement down in the low millivolt range.

Thermocouples, however, are generally more accurate and do not require calibration, since their voltage output is set by physics. But the circuit or device used to measure their output does require calibration.

Answer 4

No.

An RTD has a stable wire like a platinum one which is known to change its resistance by a certain number of Ohms per degree Celsius. You take a coil of that platinum that is know to have a resistance of 100 Ohms at a standard temperature, check its resistance at the temperature you are observing, and see how many degrees are needed to account for the new resistance.

A thermocouple is a pair of two wires with different EMF constants (like Iron and Constantin) that are touching. When put into an elevated heat they will generate a small voltage at their junction. Measuring that voltage will tell what the temperature is