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Facility for the measurement of the refractive index of glass prism
No full textIl manufatto presentato consiste in una stazione di misura dell'indice di rifrazione di prismi in vetro con una incertezza relativa migliore di 1 ppm, allestita all'INRiM nel 2008.A facility for the measurement of glass refractive index with a relative standard uncertainty better than 1 ppm implemented at INRiM in 2008 is presented
Angle amplification for nanoradian measurements
No full textA method to amplify the rotation angle of a mirror, based on multiple reflections between two quasi-parallel
mirrors, is presented. The method allows rotations of fractions of nanoradians to be measured with a simple
setup. The working principle, the experimental setup, and the results are presented
The new INRIM rotating encoder angle comparator (REAC)
Full text linkA novel angle comparator has been built and tested at INRIM. The device is based on a double air bearing structure embedding a continuously rotating encoder, which is read by two heads: one fixed to the base of the comparator and a second fixed to the upper moving part of the comparator. The phase measurement between the two heads’ signals is proportional to the relative angle suspended between them (and, therefore, the angle between the base and the upper, movable part of the comparator). The advantage of this solution is to reduce the encoder graduation errors and to cancel the cyclic errors due to the interpolation of the encoder lines. By using only two pairs of reading heads, we have achieved an intrinsic accuracy of ±0.04′′ (rectangular distribution) that can be reduced through self-calibration. The residual cyclic errors have shown to be less than 0.01′′ peak-to-peak. The random fluctuations are less than 0.01′′ rms on a 100 s time interval. A further advantage of the rotating encoder is the intrinsic knowledge of the absolute position without the need of a zeroing procedure. Construction details of the rotating encoder angle comparator (REAC), characterization tests, and examples of practical use are given
Prism refractive index measurement at INRiM
No full textA simple method to measure the refractive index of a glass prism with very low uncertainty was developed at INRiM. The method is a modification of the classical minimum deviation method. A brief description of the methods used to measure the vertex angles of the prism and
the angle of minimum deviation is reported together with the uncertainty evaluation. The technique is going to be validated by a comparison between INRiM and two other laboratories.
A relative standard uncertainty better than 1 ppm has been obtained
Validation of a novel technique for the measurement of the refractive index of a prism by means of interlaboratory comparison
No full textA new method to measure the refractive index of glass prism with very low uncertainty was developed at INRiM. The method is based on a modification of the classical minimum deviation method. In order to validate the technique, an interlaboratory comparison
between INRiM and two other laboratories started in February 2008. Three prismatic glass samples with nominal refractive index at 633 nm of 1.515 were sent to each participant one by one, the homogeneity of the base glass material used to fabricate the prisms being
better than 10^(-6). Each participant was asked to measure the refractive index of the prism with its own technique at 633 nm at 20 and 23 °C. A brief description of the method developed
at INRiM and the evaluated uncertainty is reported together with the first preliminary results of the comparison
The new INRiM nanoangle generator
No full textAt the angle metrology laboratory of the Istituto Nazionale di Ricerca Metrologica (INRiM, formerly IMGC), an instrument to generate very small angles has been recently developed.
It is a sine-bar angle generator based on an elastic hinge and a piezocapacitive device. The facility can be used to calibrate precise angle measuring instruments (levels, autocollimators, etc) in a range of 120 μrad with an uncertainty of about 20 nrad and a sensitivity of fractions of a nanoradian. The working principle and metrological characterization are presented
The combined use of a gas-controlled heat pipe and a copper point to improve the calibration of thermocouples up to 1100 °C
No full textThe calibration of platinum-based thermocouples from 420 °C to 1100 °C is currently carried out at INRIM making use of two different apparatus: for temperatures
below 930 °C, a potassium gas-controlled heat pipe (GCHP) is used, whereas a
metal-block furnace is adopted for higher temperatures. The standard uncertainty of the reference temperature obtained in the lower temperature range is almost one order of magnitude better than in the higher temperature range. A sealed copper cell was investigated to see if it could be used to calibrate thermocouples above 930 °C with a lower uncertainty than our current procedures allowed. The cell was characterized with Type S and Pt/Pd thermocouples and with an HTPRT. The freezing plateaux were flat within 0.01 °C and lasted up to 1 h with a repeatability of 0.02 °C. The temperature of the cell was determined with a standard uncertainty of 0.04 °C. Hence, the copper cell was found to be superior to the comparator furnace for the calibration of platinum-
based thermocouples because of the significant decrease in the uncertainty that it
provides. An analysis was also carried out on the calibration of Pt/Pd thermocouples, and it was found that the combined use of the potassium GCHP and the Cu fixed-point cell is adequate to exploit the potential of these sensors in the range from 420 °C to
1084 °C. A comparison with a fixed-point calibration was also made which gave rise
to agreement within 0.07 °C between the two approaches
On the Use of the Co-C Fixed Point for Calibration of Pt/Pd Thermocouples
No full textAt INRIM, different Co–C fixed-point cells have been constructed and investigated. Two cells of different design and volume and filled with highly pure cobalt (99.998%) were used to extend the fixed-point calibration of five Pt/Pd thermocouples that had been previously calibrated at the triple point of water and at the fixed points of In, Sn, Zn, Al, and Ag. The calibration at the Cu point was also added during
this exercise. Because a previous calibration from 962 °C up to 1500°C against
the local standard radiation thermometer was available, a comparison was possible
with the Co–C fixed-point calibration. Agreement within 0.10 °C was found when the
value of 1324.0 °C, the same value proposed for the Co–C point to be included as a
secondary reference point of the ITS-90, was assumed
Facility for the calibration of Pt/Pd thermocouples in the temperature range from 960 °C to 1500 °C
No full textFive Pt/Pd thermocouples, constructed and calibrated at IMGC at fixed points in the temperature range from 0 °C to the Ag point, were calibrated by comparison with the local primary standard radiation thermometer with
the aim of replacing the presently used Pt/Pt–Rh alloy thermocouples as secondary reference standards up to 1500 °C. To fully exploit accuracy of Pt/Pd thermocouples, high-level calibration techniques need to be adopted. For this purpose, a new high-temperature three-zone furnace was arranged
and characterized in order to obtain the best axial uniformity and a specially
designed blackbody cavity was used as a transfer source for calibrating the thermocouples in the temperature range from 962 °C up to 1500 °C. At the
end of the comparison measurements, additional calibrations at the Ag fixed
point were made, in order to check the stability of the thermocouples’signals. A comparison between experimental results and the reference function is presented and an extrapolation of the fixed-point calibration data
is analysed
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