A pyrometer is a device that measures temperature using a non-contact method. They are often used in industrial applications to measure the temperature of very hot objects such as red-hot steel, molten glass or objects heated in furnaces. Pyrometers work by detecting the infrared (IR) radiation emitted by an object and using this information to calculate its temperature. They are highly accurate and can directly measure the temperature of all types of materials over a wide temperature range. Pyrometers are used in many industries where accurate, non-contact temperature measurement is essential for the correct thermal processing of materials and to optimise energy efficiency.
There are several different types of pyrometers; each specifically optimised to suit a particular application. Broadly speaking, there are four main types of pyrometers:
- Single-colour or single-wavelength pyrometers
- Dual-colour, dual-wavelength or ratio pyrometers
- Fiber optic pyrometers
- Transfer-Standard Pyrometers (TSPs)
Explore Our Range of Impac Pyrometers at LIMAB UK
Single-Colour Pyrometers
A single-colour pyrometer — sometimes referred to as a single-wavelength pyrometer — measures the IR radiation emitted by an object at one wavelength only. Different models covering different spectral ranges or wavelengths need to be selected according to the material being measured and the temperature range. When selected correctly for given applications, a single-colour pyrometer will provide excellent measurement accuracy.
Dual-Colour Pyrometers
A dual-colour pyrometer (also known as a dual-wavelength or ratio pyrometer) uses two single-colour pyrometers to simultaneously measure an object’s temperature across two different wavelengths.
A dual-colour pyrometer calculates the temperature from the two signals using a rationing technique. By rationing the signal of the two detectors, the pyrometer measures the colour distribution instead of just the signal intensity. This makes the measurement independent of factors that affect the signal intensity, such as contaminants in the air between the object and the pyrometer, such as dust, steam or smoke. For some applications, it also means the pyrometer is not affected by emissivity changes as there is a neutral change in both channels.
Some ratio pyrometers can be used in different modes: single-colour, dual-colour or smart mode. This is to optimise the measurement performance depending on the intended application and to enhance the application range of the pyrometer.
Advantages of Dual-Colour Pyrometers
There are several advantages of dual-colour pyrometers over single-colour pyrometers:
Not affected by contaminants in the air. For many applications where materials are heated, there are fumes, smoke, steam or dust in the air between the object being measured and the pyrometer that cannot be avoided. For these applications, a dual-colour pyrometer should always be selected.
Not affected by contaminants on the optics. In some processes where the pyrometer will be used, it is known that the optics will become contaminated. Although it is possible to reduce the contamination by using an air purge, the reliability of the measurement and maintenance period can be extended by using a dual-colour pyrometer.
Better suited for measuring very small objects. When using a single-colour pyrometer, the object must be bigger than the measuring spot. A temperature measurement error will occur if the full spot is not on the object. A dual-colour pyrometer will continue to correctly measure the temperature if part of the spot is not on the object.
Able to cope with emissivity changes. In some industrial applications, it is possible for the emissivity of the material to change. If this happens, the accuracy of a single-colour pyrometer measurement will be affected unless the emissivity setting is adjusted accordingly. However, in many applications, dual-colour pyrometers can cope with this without the accuracy being affected.
We advise discussing the details of your application with one of our product specialists, who can provide you with a recommendation for your specific requirements.
Fiber Optic Pyrometers
A fiber optic pyrometer is one in which the optics and electronics are separate but connected by means of a fiber optic cable. The IR radiation is collected by the optics and guided to the detector via a flexible fiber optic cable. As the receiving optics do not contain any electronics, it is a more compact size and able to withstand higher ambient temperatures.
Fiber optic pyrometers are suitable for a wide range of applications where it is too dangerous or difficult to measure temperature using a standard pyrometer and are available in single or dual-colour versions. They are often used in applications where they are close to induction heating coils, as the fiber optic cable is not affected by the high electromagnetic radiation emitted by this type of heating method. They are also often used in other high-temperature applications such as boilers, burners, industrial furnaces and kilns, where using a traditional pyrometer would not be possible due to the extreme heat and proximity of the electronics.
Transfer-Standard Pyrometers
TSPs are the most accurate type of pyrometer and are used to calibrate other pyrometers. They do this by taking the reference temperature from a blackbody and transferring this reference to another pyrometer that needs their measurement verified. Blackbodies are devices that emit radiation at a known temperature, providing an accurate temperature reference for calibration. TSPs have a resolution of 0.01°C with extreme accuracy and long-term stability and are provided with traceable calibration certificates.
Choosing the Right Type of Pyrometer
The industry, the type of material being measured and the temperature range required are all factors that affect which type of pyrometer is most appropriate. Our product specialists can advise which pyrometer is most appropriate for your needs.
Learn More about Pyrometers
In summary, pyrometers are versatile devices for accurate, non-contact temperature measurement that can be used in a wide range of applications. Single-colour pyrometers are suitable for applications where ease of use and cost are a priority, while dual-colour pyrometers are best suited for challenging applications or installations where there are fumes, dust or steam between the object and the pyrometer. Fiber optic pyrometers are not affected by large electromagnetic fields surrounding induction heating devices, and TSPs — as the most accurate type of pyrometer — are best suited to calibrating other devices. Each type of pyrometer has its unique characteristics and benefits, and each model within a specific category will also differ, operating and measuring within a precise spectral and temperature range.
You can learn more about pyrometers by using the links below:
- Learn more about how pyrometers work
- Learn more about the advantages of pyrometers compared to contact thermometers
- Learn more about what information you need to select the correct pyrometer
- Learn more about spot size when selecting a pyrometer
To learn more about LIMAB UK’s range of non-contact pyrometers, please visit our temperature measurement page.
To speak to a product specialist and find out how a pyrometer could benefit your company, call +44 (0)1823 668633.
