PNI RM3100 Evaluation Board - Manual (Page 9)

PNI Sensor Corporation Doc 1017252 r02
RM3100 Evaluation Board User Manual Page 8 of 33
4 RM3100 Evaluation Board Overview & Set-Up
This section provides an overview of how to set-up the RM3100 Evaluation Board and the basic
I
2 C and SPI communications requirements. For a discussion of PNI’s magneto-inductive sensor
technology, please refer to either the RM3100 Geomagnetic Sensor User Manual or PNI’s
whitepaper “Magneto-Inductive Technology Overview”, both of which can be found on PNI’s
website at www.pnicorp.com .
4.1 PCB Orientation and Output Polarities
The arrow printed on the RM3100 module indicates the intended line-of-sight. The RM3100
module is arranged in a north-east-down (NED) coordinate system, and the arrow is parallel
to the x-axis sensor. When the module is pointing directly magnetic south the x-axis reading
will be maximized and the y-axis will be zero. Likewise, when the module is pointing west
the y-axis reading will be maximized and the x-axis reading will be zero. The z-axis reading
will depend on the dip angle at the given location. At the geo-magnetic equator, where
Earth’s magnetic field is horizontal, the z-axis reading will be zero when flat.
4.2 Local Magnetic Field Considerations
Because the RM3100 sensor module measures magnetic field, it is important to consider
what items in the vicinity of the module can affect the sensor readings. Note that magnetic
field drops off as (1/distance)
3
. Specific issues to consider include:
The sensors have a specified linear regime of 200 T. (Earth’s field is ~50 T.) To
ensure the sensors operate in their linear regime, do not place the RM3100 close to
large electric currents, large masses of ferrous material, or devices incorporating
permanent magnets, such as speakers and electric motors.
Locate the RM3100 Eval Board away from changing magnetic fields. If this is not
possible, but the local magnetic field is known to have multiple states, try to take
readings only when the field is in a known state. For instance, if a motor runs part of
the time, take readings only when the motor is in a known state.
If you are uncertain about the effect a specific component may have on the system,
place the RM3100 Eval Board on a firm surface and gradually bring the component in
question close to the board, then note when the magnetic field starts to change. If the
component cannot be moved, then gradually move the RM3100 module towards the
component, carefully ensuring the orientation of the board remains constant while
doing this.