PTB at Sinsheim Control

One of the most important trade fairs of its kind, the international quality assurance fair "Control", will be held at Sinsheim from May 4 to 7, 1999. More than 700 exhibitors from 18 countries will present instruments and systems for the fields of quality assurance and testing. The "Control" which is regarded as the "informal mouthpiece" of the quality assurance and quality management community is an ideal forum for business and for the exchange of information.

The PTB, too, will again be present at this fair and inform about the work performed by it. Members of the PTB staff will be available for discussions about the tasks of PTB and of the Deutscher Kalibrierdienst (DKD, German Calibration Service), and they will answer questions concerning accreditations, tests and certifications. Two recent developments from the PTB department of industrial metrology will be presented as examples of latest results of PTB research work:

Portable diode laser for length measurements

In the field of length measuring techniques, lasers which emit light of a defined wavelength are today preferably used as length standards. The PTB has developed a diode laser which is controlled via a digital signal processor. The diode laser which is automatically stabilized by a processor to a rubidium absorption maximum, emits a wavelength of 780,24383 nm, with an uncertainty of measurement of 0,00002 nm and an optical radiant power of a few 10 mW. The digital control and the miniaturized design allow the instrument to be used by everybody at almost any place.

Dilatometer for the measurement of thermal expansion coefficients

Dimensional metrology requires that the coefficients of the thermal expansion of different workpieces be known. A measuring setup developed at PTB now allows this measurand to be determined in an easier and more cost-effective way than has so far been possible. The workpiece and a reference standard are heated from 19 °C to 26 °C and then cooled again down to 19 °C. The changes caused by this temperature variation are determiend by a simple measuring setup: A Zerodur rod - with a thermal expansion coefficient close to zero - is provided with three feet which firmly rest on the test specimen. One of the feet is designed as a torsion spring which is deflected when the workpiece to be examined expands. This deflection in turn deforms strain gauges fixed to the torsion spring. This change in the strain gauges leads to a voltage change which is recorded by a computer. The measured voltage and temperature values of reference standard and workpiece are offset against one another. As the thermal expansion coefficient of the reference standard is known, the expansion coefficient of the test specimen can be calculated, and this with an uncertainty of about 1 · 10^-7 K^-1.