Information about thermocouple and RTD abd its application

1. THERMOCOUPLE AND
RTD

2. THERMOCOUPLE
• A thermocouple is a temperature-measuring device consisting of two dissimilar
conductors that contact each other at one or more spots. It produces a voltage when
the temperature of one of the spots differs from the reference temperature at other
parts of the circuit.
• It converts heat energy into electrical energy.
• Most widely used device for the measurement of temperature.
• Depending on the metal wires used, a Thermocouple is capable of measuring
temperature in the range –200°C to +2500°C.

3. APPLICATIONS:-
• 1. Steel industry
• 2. Gas appliance safety
• 3. Thermopile radiation sensors
• 4. Manufacturing
• 5. Power production
• 6. Thermoelectric cooling
• 7. process plants
• 8. Thermocouple as vacuum gauge

4. WORKING PRINCIPLE OF THERMOCOUPLE
•When two wires composed of dissimilar
metals are joined at both ends and one of the
ends is heated, there is a continuous current
which flows in the thermoelectric circuit. If this
circuit is broken at the center, the net open
circuit voltage (the Seebeck voltage) is a
function of the junction temperature and the
composition of the two metals. Which means
that when the junction of the two metals is
heated, or cooled, a voltage is produced that
can be correlated back to the temperature.

5. PRINCIPLE OF OPERATION:-
• SEEBECK EFFECT
• Thermocouples are based on the principle that
two wires made of dissimilar materials
connected at either end will generate a
potential between the two ends that is a
function of the materials and temperature
difference between the two ends.

6. HOW CAN TEMPERATURE DIFFERENCE CREATE
VOLTAGE ??
• When a thermoelectric material is exposed to a temperature gradient — for
example, one end is heated, while the other is cooled — electrons in that material
start to flow from the hot end to the cold end, generating an electric current. The
larger the temperature difference, the more electric current is produced, and the
more power is generated. The amount of energy that can be generated depends
on the particular transport properties of the electrons in a given material.

7. RTD (RESISTANCE TEMPERATURE DETECTOR)
• A Resistance Temperature Detector (also
known as a Resistance Thermometer or RTD)
is an electronic device used to determine the
temperature by measuring the resistance of an
electrical wire. This wire is referred to as a
temperature sensor. If we want to measure
temperature with high accuracy, an RTD is the
ideal solution, as it has good linear
characteristics over a wide range of
temperatures.

8. SOME NOTICABLE POINTS ABOUT RTD
• The RTD’S resistance increases linearly when the temperature increases.
• RTD’s consist of fine wire wrapped around a glass or ceramic core. The wire is
made of platinum.
• The RTD elements are normally housed in a protective probe to protect them
from environment they are immersely in and to make them more Robust.
• Inexpensive RTDs are called as thin film RTDs.

9. HOW DOES A RESISTANCE THERMOMETER WORK ?
• Let’s now explore how an RTD works:-
• As we mentioned an RTD comprises a resistance element
and insulated Platinum wires. Sometimes RTDs can have
three or even four wires to increase accuracy allowing
connection lead resistance errors to be eliminated. The
resistance element is made of platinum because it is very
long-term stable and it has a linear relationship between
temperature and resistance, has a wide temperature range
and it has a chemical inertness

10. RTD WORKING PRINCIPLE
• the RTD follows a basic principle. When the
temperature of a metal increases, the resistance to the
flow of electricity increases as well. An electrical
current is passed through the sensor, the resistance
element is used to measure the resistance of the
current being passed through it. As the temperature of
the resistance element increases the electrical
resistance also increases.

11. SOME KEY POINTS IN CONCERN TO RTD:
• The electrical resistance is measured in Ohms.
• The resistance value can then be converted into
temperature based on the characteristics of the
element.
• Usually, the response time for an RTD is between 0.5
and 5 seconds. This makes them very suitable for
many applications.

13. ThermoCouple RTD
A thermocouple can measure a
larger range of temperatures.
The measuring range lies
between −180 °C to 2,320 °C.
RTD is more suited to measure
lower ranges of temperature. The
measuring range of an RTD lies
between -200°C to 500 °C.
Thermocouples have poor
stability with results less
repeatable over time.
RTD exhibits very good stability
with low amounts of shifts
Thermocouples have poor
accuracy.
RTD is more accurate than a
thermocouple.
Thermocouples have poor
sensitivity, which means that a
small change in temperature is
not recognised by it.
RTD is very sensitive and can
register small changes in
temperature.

14. ThermoCouple RTD
The reaction time of a thermocouple is faster
than that of an RTD.
RTD has a good response time.
The output of a thermocouple is non-linear The output presented by an RTD is linear.
A thermocouple is cheaper than an RTD. RTDs are more expensive than thermocouples.

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