An infrared thermometer (pyrometer) is an optical instrument that measures the infrared radiation emitted by an object and converts this quantity into a temperature. Basically, hot object emits more infrared radiation than cold object. Nonetheless, the relation between the infrared radiation flow and the real temperature of the object depends also on the material itself and to be more exact depends on its emissivity. For instance, a piece of aluminium (low emissivity) and black bottle of glass (high emissivity) behave differently when exposed to radiation heat like sunlight. The black bottle gets hotter faster than the aluminum. This phenomenon is driven by the emissivity of the material. Therefore, with a single colour pyrometer it is absolutely necessary to set the correct emissivity of the object before making any measure.

Once this statement is made, the question is then: how can I know or determine this emissivity? Should I find this value in a book? Should it be detected by the instrument? Does it have a huge impact on the accuracy?To deal with this problem, one of the simple solution is to use an Emissivity Calculator. With this simple tool, you will be able
- to set the correct emissivity when installing for the first time your instrument.
- to calculate the measuring error if the emissivity of the material change (oxidation, change of the surface…).

The Emissivity Calculator is available in the KITS app for Android and iOS devices:
https://www.keller.de/en/its/tools/kits-app.htm

You can also find it in the "Tools" section of our homepage:
https://www.keller.de/en/its/tools/emissivity-calculator.htm

In a stove dome, air is heated to approx. 1300 °C before feeding into the blast furnace of a steel plant. The temperature of the grating refactory bricks is measured optically using pyrometers. These are mounted on the cupola of the hot-blast stove. Two redundant devices are often used, which are installed in parallel in a protective and a mounting fitting.

Due to extreme metrological conditions, high requirements are placed on the measuring system. The devices are exposed to external weather conditions. Depending on the country and geographic region, the ambient temperature can be between -40 ° C and +80 ° C. High dust concentrations can occur in the stove dome. Therefore modern pyrometers are used, which work according to the two-colour measurement method. These react to such disturbing influences as far as possible insensitively. A weakening of the infrared radiation by dust or smoke in the field of view or a contamination of the viewing window leads directly to a reduced temperature indication with a conventional single colour pyrometer. A two-colour pyrometer delivers reliable measured values even with a signal weakening of 90 %.

In order to keep the protective glass and the sight tube free of impurities, nitrogen is blown into the mounting fitting through a nozzle. Due to the two operating states of the stove dome during the heating of the storage stones and during the generation of hot air, the pressure in the stove dome varies between normal pressure and an overpressure of up to 5 bar. The nitrogen consumption is correspondingly high in order to generate the necessary counter-pressure. Thanks to an actually simple yet ingenious invention, KELLER ITS has succeeded in reducing the amount of gas by at least 80 %. For this purpose, a pinhole aperture with two openings is installed between the mounting flange of the stove dome and the mechanical valve. The reduction of the free opening also significantly improves the cleaning effect. In the event of a leak in the mounting valve, the perforated screen also allows considerably less dangerous hot gas to escape from the stove dome in the event of a malfunction.

A flange with one viewing window per pyrometer is installed for pressure-tight sealing. A pneumatic valve closes the opening to the stove dome in the event of a pressure loss in the purge gas, a power failure or an impermissibly high ambient temperature. This is to prevent the measuring system from being damaged by escaping hot air at temperatures up to 1300 °C.