PNI RM3100 Sensor Suite - Manual (Page 17)

PNI Sensor Corporation Doc 1017252 r03
RM3100 & RM2100 Sensor Suite User Manual Page 16 of 45
Figure 4-2: RM3100 reference schematic – I 2 C Configuration
A Sen-XY-f or Sen-Z-f sensor coil serves as the inductive element in a simple LR relaxation
oscillation circuit which is composed of an external bias resistor along with digital gates and
a comparator internal to the MagI2C. The coil’s inductance is a function of the magnetic
field strength. As such, the frequency of oscillation of the circuit varies with the strength of
the total magnetic field parallel to the sensor. To make a measurement, one side of the coil is
grounded while the other side is alternately driven with positive and negative current through
the oscillator. The circuit is driven for a set number of circuit oscillations, and the time to
complete the oscillations is measured using the MagI2C’s internal high-speed clock. The
MagI2C next switches the bias connection to the coil and makes another measurement. The
side that was previously grounded is now charged and discharged while the other is now
grounded.