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The PTB at the MTQ '98 in Dortmund

Hall 5, Stand 5052 telephone.: 0231/2210 460

16.11.1998

The 7th International Quality Assurance Fair, the MTQ '98, takes place at the Dortmund exhibition centre Westfalenhallen from November 17 to 20, 1998.

The MTQ, an outstanding interdisciplinary forum for measurement and testing in the field of quality assurance, this year presents the latest technical solutions achieved in this field. Sectors of priority of this year's fair are testing, measuring, analysis, control, weighing, ultrasound, X-ray and C-techniques. In addition to exhibitors from the producing industries, a great number of persons from the tertiary sector, i.e. from testing laboratories, organizations, associations, technical and scientific societies and publishing houses, is present at the fair and attracts the interest of the predominantly professional visitors.

The fair is accompanied by an extensive lecture programme, within the scope of which famous experts deliver lectures on subjects of immediate interest concerning "measurement and testing techniques in the field of quality assurance" and are available for discussions with other experts.
Almost at the same time (from November 18 to 20), the FLUID TRANS/MOTION CONTROL - the trade fair for hydraulics, pneumatics, motive power and compressed-air engineering and automation, takes place in hall 7.

As in previous years, the PTB uses the MTQ to present itself and the results of its research work. On the stand at the fair, PTB staff members offer information on the tasks and organization of the PTB and the Deutscher Kalibrierdienst (DKD, German Calibration Service), answer questions regarding accreditation, mutual recognition of calibrations, tests and certifications etc., and are at the visitors' disposal for discussions about technical problems as encountered in the calibration of measuring devices.

In addition to publications and graphs reporting on tasks and research results of immediate interest, the PTB exhibits two objects.

DSP-controlled rubidium-stabilized diode laser for length measuring technology

Digital signal processing which has increasingly become part of everyday life offers some advantages over the analog technique, for example flexibility as a result of software changes, exact reproducibility and high accuracy. A drawback is the quantizing noise. Furthermore, the frequency range in which digital signal processors (DSP) can be used is limited but the DSPs become ever more efficient. Thus the present-day communication technology is not imaginable without digital signal processors. The diode laser as a light source has advantages as regards miniaturization, useful life, costs, efficiency, radiant power, modulation capability, high-voltage-free operation, etc. Drawbacks of diode lasers are the scattering of the emitted wavelength, their relatively strong dependence on the diode parameters, injection current and temperature, and their temporal variation even if the diode parameters are kept constant. These disadvantages can be compensated by stabilization of the wavelength by link-up with an atomic absorption line, for example rubidium (Rb). The diode laser thus is an interesting alternative to the He-Ne gas lasers which are mostly used in length measuring technique.

A portable DSP-controlled Rb-stabilized diode laser has been developed, set up and tested in cooperation between the PTB in Braunschweig and the Braunschweig-Wolfenbüttel Technical College for use in precision length measuring technology. A DSP ensures the control and stabilization of a diode laser to an Rb absorption line so that the lay public could also operate this device. After the diode laser has been switched on, its wavelength is automatically stabilized to an Rb absorption maximum. The diode laser developed as a length standard emits a wavelength of 780,243 830 nm with a relative uncertainty of measurement of ±2 · 10-8.

Device for the ultra-precise measurement of temperature and other environmental parameters, for example for the purposes of high-resolution length measuring technology

The temperature measuring device was specially developed for industrial metrology, where it is used, for example, in the field of high-resolution length measuring technology. All functions required for this purpose and the relevant specifications were taken into account, and an economic solution was found which meets the requirements of practice.

The device makes available a number of measuring channels (up to 64) which can be selected at will. Various new approaches (e.g. zero current correction) allow the high demands on the measurement accuracy to be complied with. The uncertainty of measurement of the electronic system (without detectors) is < 0,3 mK. For an optimal solution of the respective measurement task, the device can be operated with different temperature detectors, distributed and arranged at will. For absolute temperature measurements and simultaneous calibration it is, for example, possible to mix Pt 100 and Pt 25 detectors (link-up with ITS 90). In addtion, thermocouples or thermistors can be used to perform high-precision measurements of the temperature differences. Moreover, in order to determine the refractive index of the air, the device can be supplemented by components which allow the atmospheric pressure, the air humidity and the CO2 contents of the air to be measured.

The measuring device is operated with a ROM-resident programme of a single-board computer which is controlled via an RS-232 interface. All measuring channels can be individually interrogated via this interface. The values determined by the detectors can be corrected and converted with the aid of different calibration functions. The calibration functions selected and the calibration values are input via the RS-232 and stored in an EEPROM which is independent of the network.