| Latest scientific news |
| • Fundamentals of metrology |
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First traceable measurements of the opto-electronic delay of PIN photo diodes
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A collaboration of the working groups ”Acceleration” and ”Terahertz Optics” of PTB realized the first experimental determination of the combined electro-optic delay of PIN photo diodes with integrated preamplifier. The results from these measurements confirm the estimates of measurement uncertainty for the primary phase calibration of accelerometers especially for high frequencies.
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Easier uncertainty estimation for specific model functions
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Common procedures for the determination of the uncertainty of measurement results usually use a model function by means of which the contributions to the total measurement uncertainty are calculated. For this purpose, the partial derivatives of this mathematical function are formed which indicate - as so-called "sensitivity coefficients" - how strongly the individual contribution enters into the overall budget. Now there are cases where there are individual contributions of the related quantity although these derivatives are zero.
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| • Metrology for economy |
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Interlaboratory comparison of 28 DAkkS calibration laboratories for weighing instruments
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According to the Units and Time Act, PTB's task is, amongst other things, to disseminate the legal units. This task is fulfilled with the support of accredited laboratories. Since 1 January 2010, the accreditation of these calibration laboratories has been the responsibility of the Deutsche Akkreditierungsstelle GmbH (DAkkS - the German accreditation body). Pursuant to DIN EN ISO/IEC 17025, calibration laboratories are expected to take all the necessary measures to ensure the quality of their calibration results. In order to comply with this requirement and to be assured of the quality of calibrations performed by accredited laboratories in the field of weighing instruments, comparison measurements were performed and the results were analysed.
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First steps towards a quantitative characterization of ultrasound cleaning vessels
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Although ultrasound baths are already in broad use in industry, trade and in the private sector, designing a device for a special purpose has so far required long series of tests and has been based on the individual empirical values of the manufacturers. The reason for this is that the underlying physical effect – cavitation – is, by nature, highly stochastic and depends on a whole series of ambient parameters. Bringing some order into the chaos has now been achieved at PTB.
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Creep measurements on precision torque transducers in comparison
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Due to internal shifting processes, torque transducers react only slowly to a changing of loads. After a change has been effected, it takes several minutes until the output signal goes asymptotically into a stable state (Figure 1). If one wants to assess the suitability of a torque transducer for dynamic or high-precision tasks, this behaviour - which is called "creep" - must be known. For that reason, DIN 51309 prescribes that during the calibration of torque transducers, corresponding creep measurements have to be carried out.
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| • Metrology for society |
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Minimum target size for ultrasound power measurements in focussed fields
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The minimum target size for power measurements in focussed ultrasonic fields with circular symmetry has been computed; such fields occur in medical diagnostics and in high-intensity therapeutic ultrasound applications.
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A new way to elicit otoacoustic emissions
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The human ear is not a passive sensory organ: If a healthy ear is stimulated by two pure tones that are a musical minor third apart, it responds by producing the fundamental of the major triad. This inaudible tone which originates from the inner ear is called a distortion product otoacoustic emission, or simply a "DPOAE", and can be both elicited and recorded by a small probe inserted into the ear canal. Conventionally, the two miniature loudspeakers in the ear canal probe are used to elicit DPOAEs. In an innovative study, we investigated a combined stimulation of otoacoustic emissions, with one tone presented as is usual by a miniature loudspeaker and the other applied by a bone vibrator placed on the cranial bone of the test person. This combined stimulation yielded detectable DPOAEs.
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Monitoring of the formation of lesions in HIFU treatments on the basis of radiated shear waves
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When using pulsed HIFU (High Intensity Focused Ultrasound), shear waves are radiated which contain information on the process of the formation of lesions. These can be used to monitor the progress of the therapy for the early detection and avoidance of irregularities.
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| • International affairs |
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- more ... coming soon
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