Response; Electromagnetic Compatibility; Performance; Signal Processing - Bartington Mag690 Operation Manual

5.3. Response

The analogue output V, for any channel, is proportional to the axial component b of the total field
F. If q is the angle subtended between the direction of F and sensing axis of the fluxgate element,
then:

5.4. Electromagnetic Compatibility

Note: The Mag690 is not shielded for immunity from, or emission of, electromagnetic
fields. Any shield placed around the sensor will limit the bandwidth of the sensor response.
The emissions generated are at a low level with a primary frequency of 15kHz, being
the frequency of the energising field of the sensor. The sensor is required to respond to
magnetic fields within the specified frequency band.
Note: Ensure that the sensor is not operated in areas where a high electromagnetic field
exists, even if the frequency is above the bandwidth of the sensor, as false information may
appear due to aliasing. This effect is seen in data acquisition systems when the frequency
of sampling is lower than the frequency of the signal which is being sampled. It may
produce apparent signals at lower frequencies than the noise, which may be within the
frequency band of the sensor. Similarly, do not place the sensor near to any equipment
which may be affected by the fields produced by the sensor excitation.

5.5. Performance

5.5.1. Signal Processing

For different applications it may be necessary to process the signal from the sensor in different
ways.
a. In order to increase the sensitivity of the recording system it may be necessary to back-
off the earth's field and amplify only the changes in the field from the current value. This
requires a high-pass filter, which could be a simple capacitively coupled arrangement or a
multi-pole filter to provide a steep roll off characteristic. These features are all present in the
SCU1 signal conditioning unit.
The output from all fluxgate sensors will contain noise from the driving electronics. For the
Mag690 this noise is at 15kHz, which is well above the bandwidth of the sensors. Where low
noise operation is required, a filter should always be provided to reject the noise which lies
outside the band of interest.
BARTINGTON INSTRUMENTS
b = F cosq and V α F cosq
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