Retsch AS 200 control - natural frequency - Manual (Page 22)

Retsch GmbH 22
Information on the sieve bottom
acceleration mode
The AS 200 control is a throwing-type sieving machine which
gives you the possibility of specifying both the amplitude and
the sieve bottom acceleration as sieving parameters.
Throwing-type sieving machines, such as the AS 200 control,
are usually based on a spring-mass system which is excited by
the natural frequency. This means that, in contrast to sieving
machines which are excited only by mains frequency, a sieving
machine excited by the natural frequency is independent of the
voltage supply.
As long as sieve analyses are to be compared or reproduced
within the respective natural frequency ranges specifying the
same amplitudes and sieving times will of course also give
comparable results.
As a result of increasing globalisation of product processes
throughout the world it is becoming more and more important
to compare sieve analyses from sieving machines excited by
mains frequencies in both mains frequency ranges 50/60 Hz
with each other, and also of course with the results of your AS
200 control, excited by natural frequency. Even if these sieve
analyses are carried out at the same amplitude and the same
sieving time, it still cannot be assumed that the results will be
comparable, owing to the different sieving frequencies at
appropriately short sieving times.
The reason for these differences is the fact that with throwing-
type sieve analyses the important parameter is not really the
amplitude but the sieve bottom acceleration. This, together
with the amplitude, is determined mainly by the frequency.
As long as sieving is carried out only at the same frequency,
e.g. at the same mains frequency, variation in the amplitude is
of course also the only possibility of varying the sieve bottom
acceleration.
To take these physical facts into account your new AS 200
control now provides you with the possibility of specifying
display and control of the sieve bottom acceleration in
addition to the amplitude. The sieve bottom acceleration is
indicated as a multiple of the acceleration due to gravity “g” (1
g = 9.81 m/s²). This functional principle is based on our
German patent no. 19 625 808.
For more detailed operation instructions see the section
“Operation of the AS 200 control and the paragraph “Sieve
bottom acceleration”.
However, comparative sieve analyses in the acceleration mode
with direct input presupposes that the sieve bottom
acceleration of the comparison machine is known (e.g. an AS
200 control or another AS 200 control).