2 introduction, Introduction – PNI RM3100 Sensor Suite User Manual
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PNI Sensor Corporation
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RM3100 & RM2100 Sensor Suite User Manual
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2 Introduction
Thank you for purchasing PNI Sensor Corporation’s RM2100 or RM3100 Geomagnetic Sensor,
pn 90052 or pn 90053, respectively. The RM2100 is comprised of two Sen-XY-f sensor coils,
pn 13104, and a MagI2C ASIC controller, pn 13156, which forms the basis for a 2-axis digital
compass. The RM3100 is the same as the RM2100 but adds a Sen-Z-f sensor coil, pn 13101,
such that compassing measurements are not constricted to the horizontal plane.
PNI’s geomagnetic sensor technology provides high resolution, low power consumption, large
signal noise immunity, a large dynamic range, and high sampling rates. Measurements are stable
over temperature and inherently free from offset drift. The RM3100’s MagI2C ASIC features
both continuous measurement mode and single measurement polling, an alarm feature for
monitoring magnetic field strength, software-configurable resolution and sample rate, and the
ability to operate one, two, or three PNI sensor coils. And it incorporates both I
2
C and SPI
interfaces for system design flexibility.
When implementing an RM3100 or RM2100 Geomagnetic Sensor, each sensor coil serves as the
inductive element in a simple LR relaxation oscillation circuit, where the coil’s effective
inductance is proportional to the magnetic field parallel to the sensor axis. The LR circuit is
driven by the MagI2C ASIC, and the MagI2C’s internal clock is used to measure the circuit’s
oscillation frequency, and hence the magnetic field. Since PNI’s Geomagnetic Sensor works in
the frequency domain, resolution and noise are established cleanly by the number of MagI2C
internal clock counts (cycle counts). In comparison, fluxgate and MR technologies require
expensive and complex signal processing to obtain similar resolution and noise, and in many
respects the geomagnetic sensor’s performance simply cannot be matched. Also, the output from
the MagI2C is inherently digital and can be fed directly into a microprocessor, eliminating the
need for signal conditioning or an analog/digital interface between the sensor and a
microprocessor. The simplicity of PNI’s geomagnetic sensor combined with the lack of signal
conditioning makes it easier and less expensive to implement than alternative fluxgate or
magneto-resistive (MR) technologies.
For more information on PNI’s magneto-inductive sensor technology, see PNI’s whitepaper
“Magneto-Inductive Technology Overview” a