This paper deals with the design of gravimetric apparatus with regard to the requirements of vacuum. Items discussed include
the calculation of suction speed and ultimate vacuum, the choice of the pump and of the method of pressure control, and the
design of the balance and the balance stand.
can be used to calculate the unknown torque T and to relate the other quantities in the equation to the actual instrument-constants. In this way, balance reading could be much faster and weighing errors due to faulty instrument and environmental influences can be smaller than those in equilibrium position. This enables the use of microbalances for the observation of fast chemical or thermal processes and to use it as fast checkweigher for control of sorting machines. In the present paper we present results from calculations of a simulation procedure.
Authors:C. Massen, C. Swüste, E. Robens, and J. Poulis
Several decades ago, when working in the field of magnetism, we had to use a balance the sensitivity of which was limited
only by Brownian motion. This balance was a very slow one and to calculate the moment of force measured by it we used its
equation of motion, T=Jα+kα+Cα, where we measured the values of all the quantities present on the right-hand side of this
equation. At the 21st Conference on Vacuum Microbalance Techniques in Dijon, we suggested that, with the help of a computer,
this procedure could also be made applicable to the handling of fast balances. The present paper contributes to this topic
by presenting a computer simulation of such a fast balance.
The basic principle of comparing the sample
mass with the mass of a reference body in equilibrium gives the equal-armed
beam balance a unique accuracy. Main parameters characterising the suitability
of the instrument are measuring range, resolution and relative sensitivity
(resolution/maximum load). The historical development of the values of these
parameters achieved depended strongly on the practical need in those times.
Technically unfavourable scales of the oldest Egyptian dynasties (~3000
BC) could resolve mass differences of 1 g and had a relative sensitivity of
at least 10–3. More sophisticated instruments
from the 18th Dynasty (~1567–1320 BC) achieved
a relative sensitivity of 10–4 independent
of the size of the instrument. In 350 BC Aristotle clarified the theory of
the lever and at about 250 BC Archimedes used the balance for density determinations
of solids. The masterpiece of a hydrological balance was Al Chazini’s
'Balance of Wisdom’ built about 1120. Its relative sensitivity
Real progress took
place when scientists like Lavoisier (1743–1794) founded modern chemistry.
At the end of the 19th century metrological balances
reached a relative sensitivity of 10–9 with
a maximum load of several kilogrammes. That seems to be the high end of sensitivity
of the classical mechanical beam balance with knife edges. Improvements took
place by electrodynamic compensation (Emich, Gast).
In 1909 Ehrenhaft
and Millikan could weigh particles of 10–15
g by means of electrostatic suspension. In 1957 Sauerbrey invented the oscillating
quartz crystal balance. By observing the frequency shift of oscillating carbon
nanotubes or of silica nanorods, masses or mass changes in the attogram or
zeptogram have been observed recently.
Authors:C. Massen, C. Swüste, E. Robens, and J. Poulis
At the 3rd Conference on Vacuum Microbalance Techniques in Los Angeles in 1962, we suggested the use of the equation of motion
of a balance T=J+α+kα+Cα for the calculation of the unknown torque T, and the measurement for that purpose of the values of
all the other quantities in this equation. The present paper discusses the consequences of two sources of error relevant for
this method. First, the errors caused in the first and second derivatives of the deflection are considered, deduced from two
or three deflection measurements separated by small time intervals. Secondly, the consequences of the errors caused by the
uncertainties in the deflection measurements are discussed. Consideration of the two errors together leads to an optimal set
of values of parameters for the balance handling.
Authors:J. Poulis, E. Robens, C. Massen, and R. Roverato
Restoring of the balance beam to its initial situation after a change of load can be effected by combination of forces of
different kind. In former papers we discussed the possibility using the equation of motion of the balance to determine the
mass to be measured. After the measurement the balance was restored by means of current pulses into the electromagnetic measuring
system. In the present paper we discuss the application of electric pulses into an additional electrostatic system.
A survey is given on important standardized definitions by which the capability of balances may be characterized. Some modifications are proposed with regard to the use of mass sensors for the continuous determination of mass variations. An important supplement is the ‘relative resolution’ introduced by Jenemann. Optimum values are presented.
One of the earliest measuring instruments used by human beings was the balance; evidence of this dates back more than 5.000
years. Initially, the weights of goods were measures rather of value than of mass. Besides yardsticks and graduated cups,
scales are today the most widespread instruments, found in almost all laboratories, factories and households. Indeed, the
balance accompanies us from birth to death.
The balance very early achieved a metaphorical meaning and was used for the comparison of ethical values. It first appeared
as an instrument in the death tribunal in Egyptian religion and later in Christianity. In the hands of the Grecian Gods, weighing
was a deciding factor as concerns victory or death. In Judaism and for the Romans, scales become the symbol of justice. Several
trade and handicraft guilds currently use the balance as an attribute, demonstrating in this way their sincerity and accuracy.
The balance is of dubious significance in astrology, as one of the signs of the zodiac.
Authors:Inis Jenemann, Susanne Kiefer, and E. Robens
The short survey covers the development of the balance since its invention in the Neolithic era. Scales have been used most
probably first as tools in trading, but already in Old Egyptian papyrus its use in techniques is documented. Its theory was
cleared by Aristotle and Archimedes and at least at that time it was used as a scientific instrument. Today the balance is
still the most widely used instrument in science and there are still improvements.
Authors:E. Robens, D. Möhlmann, Th. Gast, R. Staudt, and M. Eger
The balance is the most widely used complex measuring instrument in
science and techniques. To install a balance on Mars is a challenge for numerous
aspects of in situ measurements in the next decade. By means of a balance
useful parameters could be determined and a variety of investigations could
be carried out there. Possible applications of a balance on Mars are reviewed.
Choice of type and demands on the balance with regard to the conditions on
Mars are discussed. The first step is to test a load cell with strain gauge