www.ahlborn.com 18
AMIR INFRARED MEASURING TECHNOLOGY
Why Infrared Measurements?
Infrared measuring instruments provide large advantages with regard to measuring tasks that cannot be solved with conventionalcontact
industrial thermometers. Examples: Measurements of very high temperatures not allowing the use of
industrial thermocouples. Measurements at surfaces with low thermal conduction and bodies with low thermal capacity. Measurements at moving, inaccessible or live parts with a high rate of response (<1s). Measurements at objects, which must not be influenced by contact measurements.
What is Infrared Radiation?
Every substance with a temperature above absolute zero emits an infrared radiation (spectralrange of wavelengths from 0.7 to 1000 µ m) that corresponds to its temperature. This range islocated below the longer red wavelength range and is not visible to the human eye. For
measurements the most interesting range is located between 0.7 and 20 µ m.The infrared radiation emitted by the test object follows the known optical rules and, therefore,can be deviated, bundled with lenses or reflected from catoptric elements. The emissivity of a test object indicates how much infrared energy has been absorbed orreleased by radiation. The value can be between 0 and 1.0. The fact that the emissivity dependson the wavelength is relevant for measurements. With increasing object temperature the radiation maximum shifts to the short waverange. Therefore, IR thermometers are equipped with filters, which allow only one particular wavelength to pass through for the
measurement. The spectral range for specific materials must be considered for the application.
The optical system of an infrared thermometer captures the energy emitted from a circular measuring spot and focuses it onto a
detector. A material with a high transmission factor is used for the lenses. The energy captured by the detector is electronicallyamplified and converted into an electrical signal. The optical resolution results from the ratio of the measuring distance to the size ofthe measuring spot. The measuring spot must always be smaller than the test object or the measuring point of interest. The higher theoptical resolution the smaller the measuring spots can be measured at further distances.
What is Intermittent Photometry?
Using intermittent photometry eliminates the thermal drift and immunes devices against thermal shock. The stability resulting fromthis, combined with noise-optimised signal processing, leads to an excellent temperature resolution and allows the measurement ofsmallest test objects and fast response times.
Ratio
Pyrometers determine the temperature from the ratio of the energy radiated in each of two wavelength ranges. This methodallows for exact measuring results, even in case of a limited view to the test object due to vapour, steam, dust, dirty windows or lenses(up to 95% reduction of meas. signal). Furthermore, test objects, which are smaller than the measuring spot (e.g. measurement atwires), or low or varying emissivities at fast moving objects, do not affect the measuring result. Line Scanners measure the object temperature along a line. Fixed installed line scanners provide coloured heat flow charts from aproduct passing under the
measuring head (e.g.
conveyors,
rotary furnaces), but can also be moved to pass above objects (e.g. heatflow chart of a house wall). The
infrared scanner measuring head AMiR 7880 scans up to 256 dots over an angle of 90°. 20 lines canbe scanned within one second. One measuring tape can be divided into 3 sectors, side by side or overlapping.
18.02
01/2007 We reserve the right to make technical changes.