Answer / kumar_abit

Both thermocouples and RTD have their specific advantages,
according to our need we have to choose for our purpose.i am
explaining below:
1.thermocouples can measure up to a temp. of 1700 degree
celcius,where as RTDs are limited to 800 degree celcius
2.Grounded Thermocouples are inheritantly tip sensitive;
while RTD elements are isolated from their sheaths. A
grounded Thermocouple will respond to a 63% step change in
temperature nearly 3 times faster than a RTD counterpart.
3.Normally rtds are costlier i.e.2.5 or 3 times than
thermocouples
4.as the case is taken onbehalf of accuracy and linearity
RTD shows improve characteristics than thermocouple.
5.Due to their linearity and virtually drift free output,
RTDs are more stable than Thermocouples.

Answer / mazhar ali

both rtd and thermocouple ranges cant b the same , but u can
say that rtd range & thermocouple range may overlap.
if in a process u need to measure a temp of 150 degrees,then
u can use both rtd of 0-300 degrees and thermocouple
0-1200degrees, but u know rtd would be cheaper,money saying
than thermocouple.

for example when u drive a bike the speedometer may be
showing 185kmph, so the gauge of 0-220kmph is better than
using 0-1000kmph, when your bike speed is max 200kmph.

Answer / kul bhushan emecon controls

Ya i am agree with 2one but the the measure difference
between RTD & Thermocouple on their working principle.
1)RTD is limited up 500-700 degree celcius it is
manufactured up to 1000 degree celcius on special cases.
2)It is mainly used for measurement up to 500 degree
celcius.
3)It is available in 2,3 or 4 wire configuration.
4)We can use transmitter or card when we are interfacing
the RTD with DCS.
5)It's accuracy is good in comparision of Thermocouple on
small Temperature ranges.
Thermocouple
1)It is based on seeback effect.
2)It is generaly use for higher Temperature ranges up to
3000 degree celcui(ceramic type thermocouple in special
case)
3)It is not a 3,4 wire device.
4)Grounded thermocouples are used where fast response is
required.(Thermocouple tip is welded with thermowell.
5)O/P is mV.

The wire is disconnected from the temperature sending unit (magnetic gauge). A voltmeter connected to the wire reads 0v. What does this indicate?

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