Vibrating
sample magnetometer: Model VSM Nuvo MK 2
A recent advance in computing
electronics combined with innovative design
has allowed the development of a VSM (vibrating
sample magnetometer) of outstanding price/performance
ratio. The instrument is an integrated system
with all the components in one compact unit
- only the computer is separate. It uses a
small cylindrical sample, 7mm in diameter
and 9mm long. It can also use disposable syringes,
in which case the sample has a volume of 0.15
ml.
The sensitivity is high and will be described
later. All the functions of the instrument
are controlled by a computer, which sets the
field, drives the vibrator, gathers the signal
from the pickup coils and then stores and
displays the result. Most of the complicated
work occurs in the program, leaving the electronics
to do the simple work. The program is simple
to use, allowing great flexibility in the
way data is gathered and displayed. The maximum
field is I Tesla.
Sensitivity: Because there is a computer
in the system the output from the coils when
digitized can be multiplied by any factor.
What limits the factor is the noise of the
system. Noise is defined as the signal that
occurs when a measurement is made with no
sample present and this becomes meaningful
when it is compared with the signal from a
sample. Water makes a good demonstration subject.
Since the holder is slightly magnetic the
empty holder is measured first. Then a measurement
of the holder filled with 0.46 ml of water
is measured. The empty holder is then subtracted
and the susceptibility of water can be measured
and compared with the known result. The water
trace gives a good idea of the noise level.
The noise level is about 0.04 x 10-6 A m2
this is equivalent to the EMU value of 40
x 10-6 G cm3.
There is a 4 decade attenuator and on the
setting of 1 the maximum moment is around
100 x 10-6 A.m2 on range 1000, the maximum
moment is around 0.1 A.m2 or 100 G cm3.
