The PTB at the Sinsheim Control from May 12 to 15, 1998

From May 12 to 15, 1998, at the Control at Sinsheim, more than 600 exhibitors will present for the 12th time recent develop-ments and trends in the field of quality assurance and production control. The great number of exhibitors will give an almost complete survey of all aspects of quality management and thus provide an ideal basis for good discussions and business transactions.

The PTB, too, will again make use of this trade fair to present itself and current research results. At the exhibition stand, members of the PTB will offer information about the tasks and organization of PTB and the Deutscher Kalibrierdienst (DKD, German Calibration Service), answer questions concerning accreditations, mutual recognition of calibrations, tests and certifications etc., and be at the visitors' disposal to discuss the technical problems involved in the calibration of measuring devices.

As examples of current research results, the PTB will present the following two exhibits:

Proton-resonance-controlled measuring set-up by for magnetometer calibration

Nuclear resonance magnetometers based on the detection of the gyromagnetic precision of certain atomic cores in a magnetic d.c. field are at present the most precise instruments for the measurement of magnetic fields. In combination with appropriate systems for the generation of magnetic fields, such as field coils, permanent magnets or electromagnets, magnetic field standards can be established which are based on a quantum effect and whose relative uncertainty is smaller than 0,0001%. The lower limit of the measurement range of commercial nuclear resonance magnetometers is at a flux density of approx. 0,1 tesla - a value which approximately corresponds to 2000 times the earth's magnetic field.

To be able to meet the demand for calibrations of magnetic systems with small uncertainties of measurement also in fields below this limiting value, a nuclear resonance magnetometer has been developed on the basis of a highly sensitive marginal oscillator, which allows even fields of about 0,002 T to be precisely measured by detecting proton resonance in weakly paramagnetic water solutions. The magnetometer is of modular design which allows adaptation to different measurement problems and facilitates the further development of individual modules. At the fair, the proton resonance magneto-meter will be presented as a part of a measuring set-up for the calibration of magnetometers based on the Hall effect.

The second important component of the measuring set-up is a newly developed, water-cooled field coil which allows fields of up to 0,15 T to be generated for two totally different curves of the field strength distribution. One of the two possible field profiles shows, about 50 mm apart, two spatially separated positions of almost identical field strength; the deviation of the fields is of the order of 0,001% and thus perfectly suited to compare magnetic sensors without having to fear an interaction of the two sensors. The other field profile allows a field of high homogeneity to be guaranteed over a range of 20 mm in the centre of the coil, as it is required, for example, for the determination of the line width of core resonance samples.

PC-controlled RD 1-PIO 24 decade capacitor

Manually operated decade capacitors with mica or plastic dielectric and an uncertainty of at best 0,05% have so far been used for the realization of capacitance values that can be preselected. These capacitors cannot be used in automated measuring devices.

The decade capacitor presented at Sinsheim Control is based on a new type of ceramic chip capacitor (Russian make). It is automated and its technical properties have been substantially improved compared with the commercial decades so far available. With the aid of a personal computer, all capacitance values in the range from 100 pF to 1,1110 (F can be set in steps of 100 pF. This allows for the first time automatic capacitance bridges to be calibrated fully automatically and with high accuracy also for non-decadic capacitance values.

The decade capacitor presented is the result of cooperation between PTB and the D.I. Mendelejev-Institute for Metrology (VNIIM) in St. Petersburg. It is of interest to calibration laboratories and scientific institutes which need variable capacitance devices.

Selected technical data: