Appendix 1: Use Of Alternative Power Supplies; A1.1. Signal/Power Ground - Bartington Mag690 Operation Manual

Appendix 1: Use of Alternative Power Supplies

Bartington Instruments power supplies provide the most suitable methods for connecting to
and operating your sensor. If you have decided to use an alternative then the information in this
Appendix is important.
Caution: Failure to follow these instructions may result in incorrect sensor readings and in
some circumstances may cause irreparable damage to your sensor, power supply, or both.
Power supplies should normally provide ±12V. For the lowest noise applications, ripple in the
output should be in the mV region. The nominal current requirements are +45mA and -18mA
with an additional current in proportion to the measured field. The additional current is 1.4mA
per 100μT per axis and will be drawn from the positive or negative supply, depending on the
direction of the field.
The maximum output voltage swing from the sensor will always be less than the supply voltage.
In the temperature range -40°C to +70°C, and with an external load of 10kΩ, the maximum
output voltage will be less than each supply voltage by up to 2V. All parameters other than the
output voltage range remain unaffected for supply voltage changes in the range from ±8 to ±15V.
The current drain is independent of the power supply voltage and the unit will operate with
input voltages down to ±8V. As the output voltage swing is limited to 2V less than the supply
voltage, for a supply of ±8V the output will operate normally with any output between +6V and
-6V, representing a field of 0.6 of the full scale value in each direction. The scaling factor and
linearity will remain at the normal value up to this saturation point. The output will remain at
the saturation level if the field is increased beyond this point. Asymmetric supplies may be used
provided that the minimum and maximum voltages are not exceeded for either polarity.

A1.1. Signal/Power Ground

The two signal/power ground conductors are connected to a common point within the sensor.
The power supply common (power 0V) should be connected to only one of them, which becomes
the power ground. The other conductor becomes the signal ground and is used as the 0V output
from the sensor. Each signal is then measured between the X, Y & Z output conductors and the
signal ground output. In this way, the signal ground carries no power supply currents.
The minimum current in the power ground conductor is approximately 25mA. On long cables,
this will give rise to an appreciable potential difference between the power supply end and
the sensor end of the power ground conductor. The use of separate power and signal ground
conductors will ensure that this voltage is not included in the voltage measured between the
signal outputs and the signal ground.
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