| News from the Annual Report 2007 |
• Fundamentals of metrology |
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Establishment of a novel force standard machine for the range from 1 mN to 2 N
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The force standard machines of PTB serve to realize the unit "newton" from so far 0.5 N to 16.5 MN. To extend this measurement range towards smaller forces, a new device was put into operation. Instead of conventional weights, modern electromagnetically compensated load cells are used for traceability. This allows force transducers to be calibrated in the range from 1 mN to 2 N with known measurement uncertainty.
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235th PTB Seminar "Zukunft der Metrologie strömender Medien" (Future of the Metrology of Flowing Media)
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Gigantic mass and volume flows of gaseous and liquid media are transported and measured in the pipeline systems and filling plants of Germany, Europe, and worldwide, and sold to the ultimate consumer. In view of the outstanding economic importance of supplying gas, water, mineral oil, heat, and – lately - also refrigeration, and in view of the political discussions on energy efficiency, energy and cost saving, future of energy supply and alternative energy sources, the metrology of flowing media is of very central importance.
Against this background, on 3 and 4 September 2007 on the historic PTB Campus in Berlin-Charlottenburg, the 235th PTB Seminar “Zukunft der Metrologie strömender Medien“ (Future of the Metrology of Flowing Media) was held with 80 participants from Germany, Austria and Switzerland.
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Adjustment of the lever arm lengths at the 20 kN·m torque standard machine
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The 20 kN·m torque standard machine of PTB ranks among the best facilities of its kind in the world. To ensure this leading position also in the future, investigations and comparisons are performed at regular intervals. In the last few years, a small asymmetry in the arm lengths of the lever (the right arm was too short by approx. 10 µm, the left too long by approx. the same amount) has been found, which has now been trickily corrected.
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Improved stability of the 1 kg vacuum mass comparator Sartorius CCL1007 with respect to short-time temperature variations
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The stability of the 1 kg vacuum mass comparator Sartorius CCL 1007 could be improved considerably for mass determinations in air by an additional thermal insulation. Mass determinations in air are now possible with standard deviations of less than 0.1 µg. Comparable results were achieved up to now only under vacuum conditions.
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Characterisation of visco-elastic materials with the aid of N-parameter-models
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When investigating building acoustical problems on downscaled models, detailed data on the mechanical properties of the used materials were needed for experimental and numerical purposes. To determine the properties such as Young's modulus and material damping a number of established measurement methods exist, partially as normative references. Unfortunately, these measurement methods usually deliver only single-number-values for a fixed frequency. Quite a number of materials can be regarded as behaving linear visco-elastically. Combining experimental measurement and numerical analysis, the visco-elastic parameters of such a material can be determined. Hence, the complex mechanical properties can be described in a wide frequency range by just a few real numbers. Parameter identification was carried out for silicone, aluminium and acrylic glass.
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Optimisation of the Ion Beam-Apparatus to Maximal Transmission
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At the ion accumulation experiment the mass of accumulated ions and thereby the measurement uncertainty is governed by the value of the ion current at the collector. In order to achieve the maximal ion current with the existing apparatus simulations and measurements were performed for optimizing the parameters gas pressure and extraction voltage at the ion source as well as the transmission of the dipole magnet.
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Building Acoustics en miniature
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Problems in building acoustics can be investigated excellently on small, downscaled models. They are more flexible, require less time and effort and are cheaper than the usual measurements carried out in large and standardized test facilities, and they are also more reliable and realistic than most computer simulations. A downscaled model of a building-acoustics wall test facility has been designed and validated according to the theory of similarity.
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| • Metrology for economy |
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First complex-valued hydrophone calibration by customer’s order
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In anticipation of the new upcoming standard IEC 62127-1, a large European manufacturer of medical diagnostic ultrasound devices has ordered the complex-valued calibration - for one of the hydrophones to be used in the manufacturer’s internal testing labs - which was successfully provided by the PTB.
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Calibration of force vector transducers with smallest uncertainties
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With the precision force transducers used so far, the force is measured in an axis predefined by the transducer construction. In the last few years, however, the demand for force transducers working with similar precision in all spatial axes (force vector transducers) has increased. In addition, torques shall be measured in the different axes. Now, corresponding transducers and - at PTB - corresponding calibration procedures shall be developed within the scope of a research project with a partner from industry.
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The hotter the engine oil, the slower the ultrasound
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As commissoned by Hella Fahrzeugkomponenten GmbH, Bremen, measurements of the ultrasound propagation speed in engine oils as a function of temperature in the range from 8°C to 153°C were performed. The data obtained are important for the estimation of the uncertainty of the ultrasound based oil-filling level measurement in car engines recently developed.
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The receiving range of sound field measurements in cavitating media
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The receiving range of a sound field measurement in a bubble cloud was determined to better employ such measurements for an optimum use of cavitation.
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Technology transfer of dynamic measuring methods
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In June, the project "Model-based calibration of accelerometers", which is supported by the Federal Ministry of Economics and Technology (BMWi) and carried out by PTB together with SPEKTRA Schwingungstechnik und Akustik GmbH Dresden ("SPEKTRA Vibration and Acoustic Systems Engineering"), will be launched. The project is promoted within the scope of the Measurement Standards Testing and Quality (MSTQ) transfer programme of the BMWi which supports the technology transfer of innovative measuring methods to small and medium size enterprises (SME).
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The new Gravity Information System (SIS – Schwere-Informationssystem)
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With the new Gravity Information System, a novel information platform is presented on the web pages of PTB. On this platform, users from metrology can inform themselves about the local intensity of the earth’s field of gravity, related to the place of use. A four-stage gravity data model, mainly composed of freely available secondary (i.e. derived) gravitational field quantities, serves as a data base.
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| • Metrology for society |
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Microphone calibration for airborne ultrasound
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By the free-field reciprocity calibration of quarter-inch measuring microphones, the basis for the realization of the sound pressure unit has been created for frequencies up to 160 kHz.
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Differences in the sound reduction in test facilities and in buildings
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It was shown by scaled model measurements that in test facilities, homogeneous building elements have a larger sound reduction than in real buildings. This is a broadband effect which decreases with increasing frequencies and amounts up to 5 dB at low frequencies.
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Working Group 1.13 "Dynamic Weighing" enters into the Era of the MID
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With the coming into force of the new Measuring Instruments Directive 2004/22/EC (MID) on 31 March 2004, Working Group 1.13 of PTB set out to prepare itself for the new development - thus already long before the planned Europe-wide implementation of this directive by 30 October 2006. At the beginning of 2005, information letters were sent out to approx. 100 manufacturers of weighing instruments in which the date 30-10-2006 was pointed out to them and in which they were asked for timely submissal of their applications. All in all, 63 applications were submitted before 30 October 2006. Although some of them were withdrawn later on and others had to be rejected, more than twenty Type Examination Certificates could be issued punctually by 30 October 2006 or in the course of the following month.
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| • International affairs |
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Extension of the bilateral agreement with Japan
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Since 1999 exists a German-Japanese agreement on the mutual recognition of the test results of non-automatic weighing instruments. The rapid metrological progress of the past few years in the field of weighing technology has made a revision necessary. For this reason, a comprehensive extension of the agreement has been signed on June 5, 2007 by PTB and the National Metrology Institute of Japan.
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