A temperature controller for density measurements is presented that allows temperature stabilities of about 10 µK to be achieved near 20°C. The controller consists of a function generator, a thermistor in a Wheatstone bridge, a differential amplifier, a lock-in amplifier, a PC and a power source for the heater. Two of the controllers are also used to stabilize an electronic temperature fixed point at 20°C that will help to compare the realizations of the 20°C temperature in different laboratories with an uncertainty below 0.5 mK.
When comparing mass standards with large volume differences the density of air is one of the largest uncertainty components for mass. The air density can be determined by direct weighing using buoyancy artefacts or it can be calculated from the CIPM 81/91 formula. A small relative difference (about 6·10 -5 ) between these two methods exists. The aim of the present work is to verify this difference and to gain experience on vacuum weighing and on the stability of weights. Two buoyancy artefacts with different volumes were utilized. The artefacts were compared in vacuum and in air. From the...
One of the most important activities at European (EA) and National level of the National Accreditation Body (NAB) is the organisation of a series of interlaboratory comparisons (ILC), to verify the measurements capability of the accredited Laboratories. In 1999, 2001, 2002, 2004 four ILCs, for the calibration of material testing machines, was organised in Italy by SIT. In the present paper the main results obtained during the ILC are discussed, in particular a regression analysis was applied to evaluate the differences on the repeatability and accuracy given by the different laboratories.
In the field of calibration, Italy participates to the European framework with SIT(Servizio di Taratura in Italia), which grants accreditation through the verification of the correctness of the calibration of the measurement instruments with reference to the National Standards maintained by the Metrological Institutes INRIM and ENEA. One of the most important activities of the National Accreditation Body (NAB) is the organisation of a series of interlaboratory comparisons (ILC), at European (EA) and National level, to verify the measurements capability of the accredited laboratories. In 2004...
The factors contributing to the uncertainty are discussed for the measurements that were conducted for the 2 MN and 4 MN force values of the very high force key comparison administered by the Comité International des Poids et Mesures (CIPM). Details of the statistical analysis by the pilot institute, NIST, are provided. Various options for calculating the reference values and degrees of equivalence are presented, accounting for the uncertainty differences associated with the comparison force transfer standards and with the force standard machines of the participating National Metrology...
A technique for calibrating force transducers under dynamic input conditions is reported and evaluated. The output of a test transducer is determined at a number of points on an applied input force ramp by comparison with a calibrated reference transducer connected in series, enabling the output sensitivity of the test transducer to be determined. Experimental results show that transducer output values obtained using this dynamic calibration technique are in agreement with those obtained using a static calibration procedure to within 0.05%. This continuous calibration technique provides an...
A force comparator was constructed using a conventional screw-driving type uniaxial testing machine. A tuning-fork type force transducer was used as the reference. A strain-gauge type force transducer was calibrated with the comparator using springs and bearings to relax eccentric forces and moments. In comparison with a conventional dead-weight type force standard machine, deviation of up to only 1 mN at the rated capacity of 50 N was observed. There were still some limitations in terms of force controlability and obstructive eccentric forces; nevertheless, the force comparator exhibited...
The laboratory of MIKES-Lahti Precision Oy has made over almost twenty years comparisons with the PTB, utilizing more than ten different force transducers. These comparisons have been made regularly every year to supervise the traceability of force. The results of these comparisons are showing different kinds of behaviours. For the traceability the most important characteristic is the stability of the sensitivity. The change of the sensitivity directly influences the measurement uncertainty and as a result affects the final uncertainty of the intercomparison. The second characteristic is the...
This paper presents a new temperature chamber in combination with the 2-MNdeadweight force standard machine (FSM) which allows testing and certification of load cells with nominal loads up to 2 MN (200 t) by the Physikalisch-Technische Bundesanstalt (PTB). This facility is unique in Europe; for the first time it offers manufacturers and customers the possibility to certify load cells with very high nominal loads as used in the heavy industry for instance. In spite of a small installation space for the temperature chamber which is limited by the construction of the FSM the temperature chamber...
The present paper describes the preliminary results of the metrological characterization of the newly design and developed force machine to realize the forces in the range 2N- 20N with an expanded uncertainty of 50 ppm. The characterization of the machine is carried out in compression using two transfer force standards of 5 and 20 Newton capacity. The calibration of the transfer standards directly against the dead weight force machine shows that the repeatability and reproducibility are better than 0.002% and 0.003% respectively, over the full range of measurement.