What is pyrometry?
Pyrometry is a field that involves the measurement of heat, specifically, it deals with measuring the temperature of objects by detecting and measuring thermal radiation, typically in the infrared spectrum, that they emit.
What are some of the physical laws important in the field of pyrometry?
Some of the important physical laws in pyrometry include the laws of blackbody, Planck, Stefan, Boltzmann, Wien, and Kirchhoff.
What factors should be considered when choosing the spectral range in pyrometry?
Factors such as the temperature of the object, the material of the object, and the environmental conditions can influence the choice of spectral range in pyrometry.
What is emissivity and why is it important in pyrometry?
Emissivity is a measure of an object’s ability to emit infrared energy. It is important in pyrometry because it affects the accuracy of the temperature measurement.
What are some sources of interference in pyrometry?
Sources of interference in pyrometry can include environmental factors like ambient temperature and humidity, as well as characteristics of the object being measured such as its surface finish or material properties.
What are some accessories used in pyrometry?
Accessories in pyrometry can include various types of sensors, mounts, and interfaces that help in the measurement process.
What is the electromagnetic spectrum?
The electromagnetic spectrum is the range of all types of electromagnetic radiation, from radio waves to gamma rays. Infrared radiation, which is used in pyrometry, is a part of this spectrum.
What is the role of the electromagnetic spectrum in pyrometry?
In pyrometry, the electromagnetic spectrum is important because it is the range in which thermal radiation, specifically infrared radiation, exists. This radiation is what pyrometers detect and measure to determine temperature.
What is a blackbody in pyrometry?
A blackbody in pyrometry is an idealized physical body that absorbs all incident electromagnetic radiation. The concept of a blackbody is used in Planck’s law and other formulas to calculate radiation and temperature.
How does Planck’s law relate to pyrometry?
Planck’s law describes the amount of spectral radiance at a certain temperature, which is used in pyrometry to calculate the temperature of an object based on the radiation it emits.
What is Stefan-Boltzmann law and how is it used in pyrometry?
The Stefan-Boltzmann law states that the total energy radiated per unit surface area of a black body is directly proportional to the fourth power of its absolute temperature. This law is used in pyrometry to calculate the temperature of an object based on its thermal radiation.
What is Wien’s law and how does it apply to pyrometry?
Wien’s law states that the wavelength at which the radiation emitted by a blackbody is at its maximum is inversely proportional to the temperature of the body. This law is used in pyrometry to determine the peak wavelength of radiation, which can then be used to calculate the temperature.
How does Kirchhoff’s law relate to pyrometry?
Kirchhoff’s law states that at thermal equilibrium, the emissivity of a body equals its absorptivity. This law is used in pyrometry to understand how an object will emit and absorb radiation, which affects how its temperature is measured.
What is the basic design of a pyrometer?
A basic pyrometer design includes a sensor that detects infrared radiation, a lens or mirror to focus the radiation, and a detector that converts the radiation into an electrical signal that can be interpreted as a temperature reading.
How does the construction of a pyrometer affect its performance?
The construction of a pyrometer, including the materials used and the design of its components, can affect its sensitivity, accuracy, and range of temperature measurement.
What is the spectral range and why is it important in choosing a pyrometer?
The spectral range is the range of wavelengths that a pyrometer can detect. It is important in choosing a pyrometer because different materials emit radiation at different wavelengths at a given temperature, so the spectral range of the pyrometer must be suitable for the specific application.
How does emissivity affect the accuracy of a pyrometer?
Emissivity, the measure of an object’s ability to emit infrared energy, affects the accuracy of a pyrometer because if the emissivity of the object is not correctly accounted for, the pyrometer may give an inaccurate temperature reading.
What are some methods to determine the emissivity of an object?
There are several ways to determine the emissivity of the material to ensure accurate temperature measurements:
The temperature of the object is first determined (measured) with a contact thermometer. Then aim the pyrometer to the object. Now adjust the emissivity knob until the same temperature is achieved in both devices. This method can only be applied to sufficiently large and accessible objects.
Coat the material or the portion of it with a special polish (coating) whose emissivity approximately equals to 1, is accurately known, and is stable up to the temperature to be measured. When the pyrometer is aimed at the object it first measures the temperature of the coated surface and then it measures the untouched part of the surface. Simultaneously, adjust the emissivity so as to force the indicator to display the correct temperature.
For measuring high temperatures, a hole can be drilled (drilling depth should be ≤ ⅓) into the object which acts as a blackbody with an emissivity of 1.0. The temperature of the drill hole is measured first, then the pyrometer measure the surface temperature. Now emissivity is so adjusted such that the correct temperature of the material is displayed on the indicator.
The emissivity of a sample object can be determined by spectrometer analysis.
Standardized emissivity values for most materials are available. These can be entered into the instrument to estimate the material’s emissivity value.
What is the function of a detector in a pyrometer?
The detector in a pyrometer receives the photon energy from the optical system and converts it to an electric signal to drive a temperature display or control unit.
How do different materials affect the emissivity in pyrometry?
The emissivity of different materials can vary significantly. For example, the emissivity of metal strongly gets influenced by wavelength and temperature. Lustrous (smooth) metal surfaces have high emissivity at short wavelengths which decreases with increasing wavelengths. Wear and tear, oxidation, rust, etc may also affect the emissivity of metals.
How is the temperature of non-luminous flames measured in pyrometry?
To measure the temperature of non-luminous flames (e.g. gas burners), spectral pyrometers can be used. This type of pyrometer measures the radiation of hot carbon dioxide in a very narrow spectral area.
What are some sources of interference in pyrometry measurements?
Some sources of interference in pyrometry measurements include additional heat sources present in the surroundings of the measuring object, the presence of dust, water vapor, smoke, and window which reduce the strength of the infrared radiations, and the target being transparent and letting additional heat pass through.
What are broadband pyrometers?
Broadband pyrometers are a type of pyrometer that have a response from 0.3 microns wavelength to an upper limit of 2.5 to 20 microns. They measure a significant fraction of the thermal radiation emitted by the object and greatly rely on the emissivity of the surface being measured.
What are narrow-band pyrometers?
Narrowband pyrometers are a type of pyrometer that measures radiation within a specific, narrow range of wavelengths. They can provide more accurate measurements for specific applications but may be less versatile than broadband pyrometers.
How can a pyrometer be calibrated?
There are several methods for calibrating a pyrometer. One method involves using a commercial blackbody simulator, which is an isothermally heated cavity having very
There are several methods for calibrating a pyrometer:
Method I: A commercial blackbody simulator, which is an isothermally heated cavity having a very small aperture, can be used as a calibrator. The emissivity of a cavity-type blackbody source is usually 0.98 or higher which makes them ideal for exact calibration tasks.
Method II: Calibrated tungsten filament lamps are commonly used as references at higher temperatures.
Method III: A reference pyrometer whose calibration is known to be accurate can be used. Adjust the output of the pyrometer until it matches the value of the reference pyrometer.
What are some sighting techniques used in pyrometry?
There are several sighting techniques used in pyrometry:
Through the lens sighting technique: In this technique, the user looks at the object in a similar way as they would through a camera. The center of the viewing area is indicated by some marks which is the target area. Filters are fitted inside for the protection of the eyes.
Pilot lights/Laser-pointer: Halogen lamp, LED, or laser can be used as Pilot lights. The light beam facilitates the user to aim at the measuring spot more quickly and precisely, and hence accurate temperature can be measured in darkness.
What are thermal detectors and quantum detectors in a pyrometer?
Thermal detectors in a pyrometer behave similarly to a thermocouple. When photons interact with the sensitive element in the thermal detectors, the temperature of this element varies which in turn modifies the property of the detector. This modification is then electrically analyzed.
Quantum detectors work on the principle of the photoelectric effect. They interact directly with the impacting photons. They are faster than thermal detectors and are mainly used for imaging systems and line scanners. The performance of these detectors is strongly affected by the variation in ambient temperature.
What is the function of the electronics in an infrared thermometer?
The function of the electronics of the infrared thermometer is to amplify, regulate, linearize, and convert the signal from the detector to an electric signal (mV or mA) which is proportional to temperature. The output of the pyrometers can be viewed with analog and digital devices.
What are some functions available in the software used with pyrometers?
Some of the functions available in the software used with pyrometers include:
Target emissivity: It can set the emissivity of the target.
Peak picker: It locates the maximum temperature of the target temperature value from a specified number of stored real temperatures in the sensor memory.
Switch off Level: The user can adjust this value, so when the temperature of the object is below this limit, the pyrometer will stop temperature measurement.
Response Time: This function is used to set the response time of the pyrometer. It is adjustable from 20 ms to 10 seconds.
Record View: This option provides data logging. The temperature and Emissivity read by both the pyrometer with time and date are displayed.
Spot size calculation: It calculates the spot size or Actual working Distance of the Pyrometer.
Analog scale: The user can select the sub-range within the basic range of the Pyrometer. Analog output will automatically adjust to the selected range.
Change sensor type: This parameter displays the pyrometer sensor type and the user can also change two-color sensors to single and vice versa within the same software.
What are the two main categories of pyrometers?
Pyrometers can generally be classified into two main categories: Broadband pyrometers and Narrowband
Broadband pyrometers are simpler and less expensive devices that have a response from 0.3 microns wavelength to an upper limit of 2.5 to 20 microns. They measure a significant fraction of the thermal radiation emitted by the object and greatly rely on the emissivity of the surface being measured.
Narrowband pyrometers operate over a narrow range of wavelengths. They are also called single-color pyrometers. The spectral response of these pyrometers is usually less than 1 micron. They are normally used for measuring glass at 5.14 μm. Metals can also be measured as their rate of emissivity is high only in a narrow band. The spectral response of the particular device depends on the type of the detector used.
What are ratio radiation pyrometers?
Ratio radiation pyrometers, also known as two-color pyrometers, measure the radiated energy of an object between two narrow wavelength bands and then calculate the ratio of the two energies. This ratio is the function of the temperature of the object. Even if the object does not fully cover the spot, the output signal will not change.
Also, the temperature measurement is independent of emissivity, so the errors caused by the emissivity variation, surface finish, and energy-absorbing materials (e.g., smoke, smog, water vapor, etc.) between the pyrometer and the target can be minimized or removed.
What are multi-wavelength pyrometers?
Multi-wavelength pyrometers are capable of measuring more than two wavelengths. They are also called spectropyrometers. The instrument compares all the measured values and then decides where the accurate temperature lies.
What are fiber optic radiation pyrometers?
Fiber optic radiation pyrometers use an optical fiber (light guide) to direct the radiation to the detector. The spectral response of these fibers is extended to about 2 microns so it is useful in measuring object temperatures to as low as 100°C.
An optical head, a glass fiber, and a signal processing unit together form a fiber optic pyrometer. The optical head doesn’t contain any electronics. It is basically used where the sighting path to the target is not clear (pressure chamber).
What are some advantages of fiber optic pyrometers?
Some inherent advantages of fiber optics over other pyrometers are:
- They are unaffected by strong electromagnetic fields and therefore can be easily used where such types of interference fields are present.
- It can be placed in hard-to-reach fields.
- As it does not carry any electrical current, it is ideal for explosive and hazardous locations.
- The optical head and the fiber are free from any electronic components so cooling is not required and hence can be used to measure high temperatures (near about 250 °C).
- The diameter of an optical fiber is small therefore a small spot size can be obtained.
What is the difference between a single fiber and multi-fiber in fiber optic pyrometers?
Breakage in the mono fiber can be immediately detected than in multi-fiber. No wear and tear is required for mono fiber but in multi-fiber, the cladding of individual fibers may get damaged due to friction amongst them. Multi-fiber optical fiber is relatively less expensive and also their minimum curving radius makes them useful in many applications.
What are some mechanical accessories used with pyrometers?
Some mechanical accessories used with pyrometers include:
- Cooling accessories: Facilitate the pyrometer to be operated at higher surrounding temperature and maintains the internal temperature of electronics in the pyrometer.
- Mounting devices: Used to fix the pyrometer in a particular position.
- Flange systems: Used to append the pyrometers to the furnaces, containers, or pipes.
- Sighting accessories: It is very helpful to sight on the spot size for the measurement of moving objects and in poor light conditions.
- Air purge units: It is attached to the front end of the sensor which protects the optics of the pyrometer from dust, smoke, moisture, and other contaminations.
- Emissivity enhancer: It is used for shiny and highly reflective metal surfaces having very low emissivity at low temperatures.
- Scanners: Scanners are used to move the spot size back and forth across the target to be measured.
What are some electrical/electronic accessories used with pyrometers?
Some electrical/electronic accessories used with pyrometers include:
- Indicators and controller: This unit displays the measured signal as temperature (°F or °C).
- Analog Converters: Converts the output signal of 2-wire equipment from 4 to 20 mA into 0 to 20 mA.
- Digital converters: Converts a RS 485 signal into a RS 232 signal.
- Gateways: permits the conversion of RS 485 signals to several bus systems.
- Calibrators: These are used to check the precision of the pyrometers.
What are some advantages of non-contact pyrometry?
Some advantages of non-contact pyrometry include:
- It records temperature within fractions of seconds (fast response time).
- It does not influence the temperature and material of the target.
- Requires less maintenance and hence a longer lifetime.
- It can measure the temperature of the moving object.
- Measurements can be taken for hazardous or physically inaccessible objects (e.g. high-voltage parts and great measurement distance).
- As it is not in direct contact with the target so high temperature can be measured.
- Being a noncontact technique, it will not tamper with the target mechanically.
How does the size of the target and distance affect the temperature measurement in pyrometry?
The size of the target and the distance from the pyrometer can affect the temperature measurement in pyrometry. If the target is too small or too far away, the pyrometer may not be able to accurately detect the radiation from the target.
The optics of a pyrometer transmit the image of a section of the target area of the measured surface to the detector. As the distance between the pyrometer and the target increases, the dimensions of the measured object determine the required spot size of the pyrometer. So the target size should be larger than the detector spot (spot size).
The distance ratio describes the size of the measuring spot at a certain distance. Also, the ratio of the distance of the measuring device from the target, and the diameter of the spot (D:S) describes the optical resolution. Better the optical resolution of the pyrometer, smaller the target can be.
To avoid errors in the measurements, the spot size should completely fill the object otherwise the sensor will read the other temperature radiation from the background.
What are some sources of interference in pyrometry?
Other than the emissivity factor, there are several other interference sources which hinder the accuracy of measurements.
Some of these factors include:
Additional heat source present in the surroundings of the measuring object (e.g. measuring temperatures of metals in industrial ovens, where the oven walls are hotter than the measuring object) strongly influence the measurements. This additional heat may get reflected off by the target and actual temperature may get affected.
If the target is transparent and there is some hot body behind it then the target will let the additional heat pass through modifying the original temperature.
The presence of dust, water vapor, smoke, and window also reduce the strength of the infrared radiations.
What are scanners used for in pyrometry?
Scanners are used to move the spot size back and forth across the target to be measured. It is used to measure the temperature of moving objects.
Maximum value storage unit is always used with scanners. Scanners can be in-built or attached to the front of the optics of the pyrometer which assists them to be used as line scanners.
What are the three categories of the IR region?
The IR region can be divided into three different categories: near-IR (NIR/Short wave), mid-IR radiation (MIR/Medium wave), and far-IR radiation (FIR / Long wave). This region is responsible for the heating effect of the sun.
What is the role of a protection window in a pyrometer?
The protection window is part of the optical system of a pyrometer. It is used to protect the internal components of the pyrometer, such as the detector and the lens, from external factors.
The material of the protection window should be chosen based on the spectral sensitivity of the sensor and the temperature range in which the pyrometer will be used. For high temperatures, quartz glass is commonly used, while for low temperatures (in the range 8.14 µm), special IR transmissive materials like Ge and ZnSe are required.
What is the function of a sighting accessory in a pyrometer system?
A sighting accessory is a mechanical accessory used with pyrometers. It is very helpful to sight on the spot size for the measurement of moving objects and in poor light conditions. Examples of sighting accessories include sight tubes, laser pointing devices, and scopes.
What is the function of a cooling accessory in a pyrometer system?
A cooling accessory is a mechanical accessory used with pyrometers. It facilitates the pyrometer to be operated at higher surrounding temperature and maintains the internal temperature of the electronics in the pyrometer.
Examples of cooling accessories include radiation shields, cooling plates, and cooling jackets.
What is the function of a sight tube in a pyrometer system?
A sight tube is a sighting accessory used with pyrometers. It is very helpful to sight on the spot size for the measurement of moving objects and in poor light conditions.
What is the function of a laser pointing device in a pyrometer system?
A laser pointing device is a sighting accessory used with pyrometers. It is very helpful to sight on the spot size for the measurement of moving objects and in poor light conditions.