Th. Gast

An Optical Instrument for Measuring the Surface Roughness in Production Control

The measuring instrument is based on the light scattering method and is most suitable for fast production control of the surface roughness. Different theoretical models of straylight reflection are addressed. An optical parameter will be calculated from the straylight distribution. Its relationship to the surface roughness is proved in practical application. The measurement technique, different types of sensors and the integration in automatic test stations are described.

Coriolis mass flow measurement of gas under normal conditions

Abstract This paper presents a new method of directly measuring the mass flow of gas using the well-known Coriolis principle, which has proved successful for mass flow measurement of liquids. The prototype consists of two U-shaped tubes, forming a device resembling very much a tuning fork, which is stimulated by electromagnetic actuators to perform autonomous bending oscillations. By this means the fluid is subjected to a radial velocity that, in combination with the axial velocity of the flow, induces harmonic Coriolis forces of the same frequency. This causes the U-shaped tube to perform torsional oscillations that superimpose on the bending oscillations. Both oscillations can be detected via electromagnetic transducers. The amplitude of the torsional oscillation induced by the Coriolis forces is very small as the density of gas is very low. It can be amplified by tuning the eigenfrequencies of torsion and bending in a control loop. This results in an amplification of the torsional amplitude by a factor of 10 2 , allowing the mass flow of gas to be measured under normal conditions.

Disturbances in weighing - Part I A survey of work presented at the preceding VMT conferences

Abstract A survey is given on disturbances which determine the accuracy of weighing in vacuum. The nature of the disturbances covers the range from fundamental to purely practical. Apart from the physical description of the disturbing phenomena, numerical estimates for beam-type balances are presented. Part I covers the following phenomena: • Brownian motion • Knudsen forces • Cavity forces • Unequal thermal expansion of balance arms • Magnetostatic effects • Radiation pressure • Vibrations of the building • Other effects Additional effects will be discussed in Part II during the 21st Conference, 1985 at Dijon.

Survey on mass determination systems: Part I. Fundamentals and history

The influence of mass and force on the frequency of vibrating bodies today is widely applied. In Part I of the survey the historical roots are reviewed and the physical principles of the several arrangements modes of operation explained.

Survey on mass determination with oscillating systems. Part II. Instruments and weighing of matter from gaseous environment

Examples of available instruments based on oscillating systems are discussed including quartz crystals, vibrating strings, ribbons and other bodies.

Surface area, density and porosity measurements using the magnetic suspension balance

SummaryThe advantage of gravimetry in the determination of surface area is discussed in comparison with the volumetric method. The magnetic suspension balance is described and new developments are presented. As an example of the application of gravimetric measurements the determination of apparent density and specific surface area before and after oxidation of a Poco graphite are described.

A Directly Weighing Suspension Balance With Frequency Variant Output

This discourse will try to discuss the following question: What are the possibilities of measuring the force acting on a free magnetic suspended solid part (Fig.1)?

Disturbances in weighing - part II

Abstract Continuing the survey of disturbances which affect the accuracy of weighing in vacuum or in controlled atmosphere (published In Thermochimica Acta 82 (1984) 1, 42-50), the present paper deals with the following phenomena: - convectlve currents In the balance case - buoyancy - sorption effects and contamination - electrostatic effects.

Magnetic coupling for a microbalance

Balances utilising the principle of free magnetic suspension can be very useful for thermogravimetric experiments, where aggressive atmospheres and high pressures are applied. Magnetic coupling systems with automatically controlled attraction can be used for direct conversion of weight into an electric signal or for the separation of object and beam balance. The magnetic suspension balance is described and a new versatile magnetic coupling system is presented. Due to its low weight, this coupling can be combined with a microbalance.ZusammenfassungMikrowaagen mit einer freien magnetischen AufhÄngung ermöglichen eine ideale stoffliche Abtrennung zwischen dem Probenbereich und dem Waagenbereich. Dadurch werden Messbedingungen zugÄnglich wie Arbeiten unter extremen Drücken und unter spezieller, insbesondere aggressiver AtmosphÄre, die besonders in der Thermogravimetrie von grosser Bedeutung sind.Verschiedene Prinzipien der freien AufhÄngung werden beschrieben und als Anwendungsbeispiel das PhÄnomen des Probenauftriebes in AbhÄngigkeit des Messdruckes dargestellt.

Measuring the density of gases with the aid of free magnetic suspension

Abstract Two types of balances for the measurement of gas densities are described. The first is derived from the well known gas density balance by the application of automatic compensation. The second uses free magnetic suspension of a hollow glass sphere, where the exciting current of the magnetic system serves as the signal for the buoyancy.