The new DC sensor developed by Spicer
Consulting is low noise and low drift. It has been designed for use with
the SC20 Control Unit to work on
SEMs, TEMs and
EBeam lithography tools to stop beam disturbances from
AC line fields and DC fields due to
trains, trams, elevators, traffic and daily changes in the Earth’s
field.
The sensor contains 3 orthogonal magneto-resistive sensor
elements inside a 3 axis bias coil to offset the effect of the background
DC field, enabling it to work in the field environment
around today’s EBeam tools. Each time the sensor is
moved to a new location the offset needs to be reset. This is a
self-calculating process initiated with a single button press on the
Control Unit
The same size as the AC sensor, the
wideband DC sensor is smaller, faster and has lower
drift than the original DC
sensor. The small size of the sensor allows it to be placed much closer to
the electron beam column. The wide bandwidth enables this
DC sensor to be used for both DC and
AC cancelling.
The wideband DC sensor can also be
used with the SC11
Sensor Interface to allow easy surveying of DC
fields. It can often be difficult to obtain good DC
data for 3 axes as the field changes are often transient, such as those
created by passing trains. The new Sensor Interface system makes it
possible to collect all 3 axes in one go, allowing direct comparison
between the axes. The new design of the DC sensor has
virtually negligiable start-up drift, meaning that it is much easier to
make long term DC field measurements right from the
start of the survey.
Noise and drift specification:
| DC drift (after 2 hour warm up) |
< 20 µG/24 hours |
| DC drift (during 2 hour warm up) |
< 250 µG typ. |
| ULF noise (.0001-.01
Hz) |
5 µG pk-pk typ. |
| Spot noise (at 50 Hz) |
0.1 µG/root
Hz | | 
