24.10.2011
The installation in a pressure-resistant enclosure allowed the standard deviation of a 10 kg mass comparator to be reduced from 20 µg to approx. 4 µg.
Multiples and submultiples of the unit of mass in the range from 2 kg to 10 kg have so far been realized and disseminated with the aid of a 10 kg mass comparator (type AX10005, Mettler-Toledo GmbH) under normal ambient conditions. This comparator is used, among other things, for mass determinations within the scope of international comparison measurements (Key Comparisons) and calibrations for national metrology institutes (NMIs), calibration laboratories and research institutions in accordance with the measurement uncertainties stated for PTB in the CMC tables of the BIPM. Under the installation conditions so far used, a pooled standard deviation of approx. 20 µg was achieved with this system, whereby clear deteriorations were often observed as a result of air pressure fluctuations caused by the weather. For the installation in a pressure-resistant enclosure, an existing recipient was reconstructed with the aid of the PTB's "Scientific Instrumentation Department". Figure 1 shows the new set-up in the open recipient. First measurements with the new set-up furnish proof of the expected improvements. The standard deviation of the comparator could be reduced to approx. 4 µg – now independent of weather influences.
Figure 1: Installation of the 10 kg mass comparator AX10005 in a pressure-resistant enclosure (here: open)
References:
[1] Calibration and Measurement Capabilities (CMC, 
http://kcdb.bipm.org/appendixC/)
Contact person:
Michael Borys, Dept 1.1, WG 1.11, E-Mail: michael.borys@ptb.de