Maija Ojanen

Spectral irradiance model for tungsten halogen lamps in 340-850 nm wavelength range.

We have developed a physical model for the spectral irradiance of 1 kW tungsten halogen incandescent lamps for the wavelength range 340-850 nm. The model consists of the Plancks radiation law, published values for the emissivity of tungsten, and a residual spectral correction function taking into account unknown factors of the lamp. The correction function was determined by measuring the spectra of a 1000 W, quartz-halogen, tungsten coiled filament (FEL) lamp at different temperatures. The new model was tested with lamps of types FEL and 1000 W, 120 V quartz halogen (DXW). Comparisons with measurements of two national standards laboratories indicate that the model can account for the spectral irradiance values of lamps with an agreement better than 1% throughout the spectral region studied. We further demonstrate that the spectral irradiance of a lamp can be predicted with an expanded uncertainty of 2.6% if the color temperature and illuminance values for the lamp are known with expanded uncertainties of 20 K and 2%, respectively. In addition, it is suggested that the spectral irradiance may be derived from resistance measurements of the filament with lamp on and off.

Spectral irradiance comparison using a multi-wavelength filter radiometer

An automatic multi-wavelength filter radiometer (MWFR) was developed at the National Metrology Centre (NMC) of Singapore to realize the spectral irradiance scale in the wavelength range from 250 nm to 1600 nm. The UV–VIS range (250 nm to 900 nm) is covered by a silicon trap detector with 17 filters, while the near IR range (900 nm to 1600 nm) is covered by an InGaAs photodiode with 7 filters. A complete run of measurements at all 24 wavelength points takes only 12 min. The spectral irradiance scales of NMC and MIKES/TKK (Finland) in the spectral range from 280 nm to 900 nm were compared successfully using this instrument. Measurement results of three standard lamps calculated using MIKES/TKKs algorithm showed excellent repeatability and very good agreement with their assigned values. It is concluded that, compared with the conventional monochromator based spectroradiometers, a properly designed MWFR with sufficient spectral coverage is a good alternative instrument for spectral irradiance comparison owing to its faster speed and better short-term reproducibility.

Double-coiled tungsten filament lamps as absolute spectral irradiance reference sources

We have developed a physical model for the spectral behaviour of the radiation of tungsten filament lamps. The model is based on Plancks radiation law, published values for the emissivity of tungsten, measurement geometry and measured values for a residual correction function. In this paper, we study the physical interpretation of the model. The studied properties influencing the lamp spectra include the emissivity data used, light recycling effect due to the cylindrical shape of the filament, transmittance of the glass envelope and the halogen gas and temperature dependence of the transmittance. It appears that in addition to tungsten emissivity, one needs to account for the bulb transmittance and the light recycling within the cylindrical filament. We did not observe any wavelength dependence of the absorption of the filling gas.

Optical temperature measurements of silicon microbridge emitters

Microbridges are miniature suspended structures fabricated in silicon. Passing a current through the microbridge can heat it up to the point of incandescence. A glowing microbridge can be used as a wideband light source. This study presents a method for optical measurement of the temperature of a microbridge. Spectroscopic measurements of microbridges are optically challenging, because the multilayer structures cause interference effects. To determine the temperature from the emitted spectrum, the emissivity was modeled with thin-film Fresnel equations. Temperatures of 500-1100 degrees C were obtained from the measured spectra at different levels of applied power. The range is limited by the sensitivity of the detectors at lower power levels and by the stability of the bridge at higher levels. Results of the optical measurements were compared with contact temperature measurements made with a microthermocouple in the same temperature range. The results of the two methods agree within 100 K.

Moisture Measurement Setup for Wood Based Materials

Abstract: We are developing a novel gravimetric moisture measurement system for wood based materials. The measurement principle is based on combining the Loss on Drying (LoD) method with complementary water loss detection systems. In our setup, air flows through a sample container containing sample material from 5 g to 400 g. The sample container is placed in a thermally controlled enclosure, which can be heated up to 200 °C. The mass loss of water is studied by weighing the sample before and after heating, and by monitoring the humidity of the air exiting the sample container with a capacitive sensor. The amount of evaporated water is also studied by trapping the water from the through-passed air in a separately weighed cold trap. The material samples can be exposed to different heating cycles in order to study different binding degrees of the water. This paper presents the measurement concept and the setup.

Uncertainty evaluation for linking a bilateral key comparison with the corresponding CIPM key comparison

A method for evaluating the uncertainty in linking a bilateral key comparison to another key comparison with several participants is presented theoretically and demonstrated with an actual comparison. Equations are derived for the uncertainties of the unilateral and mutual degrees of equivalence for the linked participant in the bilateral comparison. It is shown that the uncertainty components related to uncorrelated effects in the measurements of the linking participant play a critical role in determining the additional uncertainties due to the linking process. As a practical example, the results are applied to a bilateral comparison of the spectral irradiance scales of MIKES (Finland) and NIMT (Thailand) in the spectral range from 290 nm to 900 nm.

Report of the Spectral Irradiance Comparison EURAMET.PR-K1.a.1 between MIKES (Finland) and NIMT (Thailand)

A bilateral comparison of the spectral irradiance scales between MIKES (Finland) and NIMT (Thailand) was carried out at 22 wavelengths between 290 nm and 900 nm. MIKES acted as the pilot and link to the results of the key comparison CCPR-K1.a. The spectral irradiance values measured by NIMT generally agree with the key comparison reference value within the expanded uncertainty. The only exceptions are results at wavelengths 300 nm, 450 nm and 500 nm, where the ratios between the degree of equivalence (DoE) and the expanded uncertainty of DoE (k = 2) are 1.0, 1.4 and 1.2, respectively. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).