This document discusses radiation pyrometers, which are devices used to measure the temperature of an object without physical contact by detecting the amount of thermal radiation emitted. It describes the basic components and working of a radiation pyrometer, including an optical system that focuses thermal radiation onto a detector which converts it to an electrical signal and temperature display. The document outlines common types of pyrometers and provides details on the construction, advantages, disadvantages, applications, and limitations of radiation pyrometers specifically.
esistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a ceramic or glass core but other constructions are also used. The RTD wire is a pure material, typically platinum, nickel, or copper. The material has an accurate resistance/temperature relationship which is used to provide an indication of temperature. As RTD elements are fragile, they are often housed in protective probes.
Resistance thermometers are constructed in a number of forms and offer greater stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a power source to operate. The resistance ideally varies nearly linearly with temperature per the Callendar–Van Dusen equation.
The platinum detecting wire needs to be kept free of contamination to remain stable. A platinum wire or film is supported on a former in such a way that it gets minimal differential expansion or other strains from its former, yet is reasonably resistant to vibration. RTD assemblies made from iron or copper are also used in some applications. Commercial platinum grades exhibit a temperature coefficient of resistance 0.00385/°C (0.385%/°C) (European Fundamental Interval).[7] The sensor is usually made to have a resistance of 100 Ω at 0 °C. This is defined in BS EN 60751:1996 (taken from IEC 60751:1995). The American Fundamental Interval is 0.00392/°C,[8] based on using a purer grade of platinum than the European standard. The American standard is from the Scientific Apparatus Manufacturers Association (SAMA), who are no longer in this standards field. As a result, the "American standard" is hardly the standard even in the US.
Lead-wire resistance can also be a factor; adopting three- and four-wire, instead of two-wire, connections can eliminate connection-lead resistance effects from measurements (see below); three-wire connection is sufficient for most purposes and is an almost universal industrial practice. Four-wire connections are used for the most precise applications.
esistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a ceramic or glass core but other constructions are also used. The RTD wire is a pure material, typically platinum, nickel, or copper. The material has an accurate resistance/temperature relationship which is used to provide an indication of temperature. As RTD elements are fragile, they are often housed in protective probes.
Resistance thermometers are constructed in a number of forms and offer greater stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a power source to operate. The resistance ideally varies nearly linearly with temperature per the Callendar–Van Dusen equation.
The platinum detecting wire needs to be kept free of contamination to remain stable. A platinum wire or film is supported on a former in such a way that it gets minimal differential expansion or other strains from its former, yet is reasonably resistant to vibration. RTD assemblies made from iron or copper are also used in some applications. Commercial platinum grades exhibit a temperature coefficient of resistance 0.00385/°C (0.385%/°C) (European Fundamental Interval).[7] The sensor is usually made to have a resistance of 100 Ω at 0 °C. This is defined in BS EN 60751:1996 (taken from IEC 60751:1995). The American Fundamental Interval is 0.00392/°C,[8] based on using a purer grade of platinum than the European standard. The American standard is from the Scientific Apparatus Manufacturers Association (SAMA), who are no longer in this standards field. As a result, the "American standard" is hardly the standard even in the US.
Lead-wire resistance can also be a factor; adopting three- and four-wire, instead of two-wire, connections can eliminate connection-lead resistance effects from measurements (see below); three-wire connection is sufficient for most purposes and is an almost universal industrial practice. Four-wire connections are used for the most precise applications.
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.
1. THERMOCOUPLE
∙ Principle of Operation
∙ Materials Used
∙ Advantages
∙ Applications
∙ Comparison with RTD
∙ Limitations
By
AnandBongir
GirjashankarMishra
2. A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference.
3. Principle of Operation
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 (also called the Seebeck Effect).
4. Seebeck Effect
5.
6. Materials Used
Type K:
Chromel – Alumel
• Range: −200 °C to +1350 °C
• Sensi: 41 µV/°C
Type J:
Iron – Constantan
• −40 to +750 °C
• 55 µV/°C
Type E:
Chromel – Constantan
• 401 to 900° C
• 68 µV/°C
Type N:
Nicrosil – Nisil
• >1200 °C
• 39 µV/°C
7. Advantages
It is rugged in construction
Covers a wide temperature range
Using extension leads and compensating cables, long transmission distances for temperature measurement possible. This is most suitable for temperature measurement of industrial furnaces
Comparatively cheaper in cost
Calibration can be easily checked
Offers good reproducibility
High speed of response
Satisfactory measurement accuracy
8. Limitations
For accurate temperature measurements, cold junction compensation is necessary
The emf induced versus temperature characteristics is somewhat nonlinear
Stray voltage pickup is possible
In many applications, amplification of signal is required
9. Applications
Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor temperatures and chemistry throughout the steel making process.
Gas-fed heating appliances such as ovens & water heaters.
In the testing of prototype electrical and mechanical apparatus
LINEAR POTENTIOMETER Potentiometers are electrical devices which are a form of variable resistance.
It consists of a sliding contact which moves over the length of a resistance element. This sliding contact connects to a plunger, which links to the object whose displacement is to be measured.
Referring to the electrical circuit shown here, An input voltage Xt is applied across the whole resistance element, at points A and C. The output voltage, Xi , is measured between the sliding contact at point B and the end of the resistance element at point C. A linear relationship exists between the input voltage Xt, output voltage Xi and the distance BC.
ANGULAR POTENTIOMETER Rotary or angular potentiometers measure angular displacement .
Optical flats are cylindrical in form with the working surfaces flat.
An optical flat may be of any transparent material usually glass with two highly polished surfaces.
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.
1. THERMOCOUPLE
∙ Principle of Operation
∙ Materials Used
∙ Advantages
∙ Applications
∙ Comparison with RTD
∙ Limitations
By
AnandBongir
GirjashankarMishra
2. A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference.
3. Principle of Operation
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 (also called the Seebeck Effect).
4. Seebeck Effect
5.
6. Materials Used
Type K:
Chromel – Alumel
• Range: −200 °C to +1350 °C
• Sensi: 41 µV/°C
Type J:
Iron – Constantan
• −40 to +750 °C
• 55 µV/°C
Type E:
Chromel – Constantan
• 401 to 900° C
• 68 µV/°C
Type N:
Nicrosil – Nisil
• >1200 °C
• 39 µV/°C
7. Advantages
It is rugged in construction
Covers a wide temperature range
Using extension leads and compensating cables, long transmission distances for temperature measurement possible. This is most suitable for temperature measurement of industrial furnaces
Comparatively cheaper in cost
Calibration can be easily checked
Offers good reproducibility
High speed of response
Satisfactory measurement accuracy
8. Limitations
For accurate temperature measurements, cold junction compensation is necessary
The emf induced versus temperature characteristics is somewhat nonlinear
Stray voltage pickup is possible
In many applications, amplification of signal is required
9. Applications
Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor temperatures and chemistry throughout the steel making process.
Gas-fed heating appliances such as ovens & water heaters.
In the testing of prototype electrical and mechanical apparatus
LINEAR POTENTIOMETER Potentiometers are electrical devices which are a form of variable resistance.
It consists of a sliding contact which moves over the length of a resistance element. This sliding contact connects to a plunger, which links to the object whose displacement is to be measured.
Referring to the electrical circuit shown here, An input voltage Xt is applied across the whole resistance element, at points A and C. The output voltage, Xi , is measured between the sliding contact at point B and the end of the resistance element at point C. A linear relationship exists between the input voltage Xt, output voltage Xi and the distance BC.
ANGULAR POTENTIOMETER Rotary or angular potentiometers measure angular displacement .
Optical flats are cylindrical in form with the working surfaces flat.
An optical flat may be of any transparent material usually glass with two highly polished surfaces.
various types of temperature measuring instrument
1.expansion types
i)bimetallic strips
ii)liquid in gas
2.based on electric resistivity
i)thermocouple
ii)thermistors(most sensitivity)
3.pyrometers
i)mirror types
ii)optical
iii)photon types(not exact names:-based on collection of photon)
and one interesting term include in pyrometers is THERMOPILE:A large number of themocouple connected in series.Hopes so you all will enjoy
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2. Radiation Pyrometer
Pyrometer:-
• A pyrometer is a device that is used for the temperature
measurement of an object.
• The device actually tracks and measures the amount of heat that
is radiated from an object.
• The thermal heat radiates from the object to the optical system
present inside the pyrometer.
• The optical system makes the thermal radiation into a better
focus and passes it to the detector.
• In an optical pyrometer, a brightness comparison is made to
measure thetemperature.
3. • The device compares the brightness produced by
the radiation of the object whose temperature is to
be measured,
• For an object, its light intensity always depends on
the temperature of the object.
• After adjusting the temperature, the current passing
through it is measured using a multimeter, as its
value will be proportional to the temperature of the
source when calibrated.
• Pyrometry is a technique for measuring
temperature without physical contact. It depends
upon the relationship between the temperature of
hot body and electronic magnetic radiation
emitted by the body.
4. Types of Pyrometer
The following are some of the most commonly and widely used
pyrometer:
1.Optical pyrometer
2.Radiation pyrometer
3.Digital pyrometer
4.Infrared pyrometer
5. Radiation pyrometer
Working construction:-
The radiation pyrometer has an optical system, including a lens,
a mirror and an adjustable eye piece.
The heat energy emitted from the hot body is passed on to the
optical lens, which collects it and is focused on to the detector
with the help of the mirror and eye piece arrangement.
6. The detector may either be a thermistor or photomultiplier tubes.
Though the latter is known for faster detection of fast moving
objects, the former may be used for small scale applications.
Thus, the heat energy is converted to its corresponding electrical
signal by the detector and is sent to the output temperature
display device.
7. Advantages:-
o Easy to operate
o High output .
o Moderate cost .
o It is simple in design and construction.
o Ability to measure high temp.
o It has Fast speed o response.
o It has no physical contact with target of measurement.
Disadvantages:-
o Emissivity errors are introduced
o It is relatively expensive.
o The radiation pyrometer is complex in nature.
o External radiation may affect the measurement.
o Emissivity of target material affecting measurement.
o It has non linear scale.
o Errors due to the absorption of radiation by carbon
dioxide, water or other apparently transparent gases.
8. Application:-
i. They are used for temperatures above the practical operating
range of thermocouples.
ii. They can be used in the environments which contaminate or
limit the life of thermocouple.
iii. Used for moving targets.
iv. They are used for measurement of average temperature of
large surface areas.
v. They are used for the targets which would be damaged by
contact with primary elements like thermocouples and
resistance thermometers.
9. Limitations of Radiation Pyrometer
1) Availability of optical materials limit on the wavelengths
that can be measured.
2) The surface of the hot object should be clean
3) It should not be oxidized.
4) Scale formation does not allow to measure radiation
accurately.
5) Emissivity correction is required.
6) Chane in emissivity with temp need to consideration.