OM1561 ISSUE 3 PAGE 3 of 11
1 INTRODUCTION – SEE FIG 1
This manual describes the operation of the
Mag
-03-OCTO-PSU power supply unit. The unit provides
a battery backed power supply of
±
12V for up to eight
Mag
-03 series three-axis fluxgate magnetic field
sensors. Signal inputs from the
Mag
-03 sensors are fully differential and the buffered outputs can be
selected to be all a.c. or all d.c. coupled. The connector pin allocation details are given in the
SPECIFICATIONS section.
2 POWER
The
Mag
-03-OCTO-PSU contains a 12V, 4Ah rechargeable Nickel Metal Hydride battery pack. The
battery is charged from the 240Vac or 120Vac mains adaptor supplied, which provides a regulated
supply of 12Vdc at 1.25A. When in good condition the battery will power eight
Mag
-03 sensors for up
to 10 hours.
A switch controls the power to the sensors. A 2.1mm input socket is provided for connecting the 12V
mains adaptor for charging the battery. The centre pin is positive and the battery pack input is protected
against reversed polarity. The sensors may be operated during battery charging provided the ambient
temperature is below 30
°
C. This is a precaution to avoid excessive internal temperatures.
A red indicator is constantly illuminated when the battery is being charged. The battery should always
be charged after use.
The +12V supply for the
Mag
-03 series of magnetic field sensors is provided by the battery pack and
the -12V supply by a dc to dc converter. Each
Mag
-03 sensor is connected by a 6-conductor cable,
the screen of which is used for the 0V power supply return (common) line. (See Figure 2)
3 FILTERS
A low pass and a high pass filter are included in the signal path of the outputs from the X, Y and Z axes
of each of the sensors. The low pass filters provide a frequency response from dc to 4.5kHz. These
filters remove the high frequency noise components of the signal from the sensor.
The high pass filters have a fixed low frequency cut off at 0.1Hz and are intended to isolate the dc or
static field component so that the alternating components above this frequency can be measured or
analysed. A switch allows the high pass filters to be de-selected or selected to provide a sensor
response from dc to 3kHz or an ac response from0.1Hz to 3kHz.
4 BUFFERS
The three XYZ signal outputs from each individual magnetometer share a common signal return line
which is separate from the power return line. In this way dc errors which could arise due to power
supply return currents are completely eliminated. The common mode rejection ratio is 50dB minimum.
The three signal lines from each magnetometer are buffered by an amplifier with a fully differential input
stage, filtered and fed via a buffer to the appropriate pin of one of the two output connectors. The signal
