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
SC12 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 |
| 
