User guide

PNIASIC
TheoryofOperation
Figure 2: Forward Bias versus Reverse Bias illustrates the change between these two measurements.
The actual magnetic measurement is the difference between these two measurements. This measurement
scheme is used to make the magnetic measurement temperature independent. It also has the benefit of
transforming the measurement range into a zero centered, positive/negative value.
The PNI ASIC returns the data to the host microprocessor over the SPI interface. The microprocessor
simply asks the PNI ASIC for data from a specific axis, and the PNI ASIC returns the data in a 16-bit 2’s
compliment format
Figure 2: Forward Bias versus Reverse Bias
When referring to axis designations PNI defines the axis in aeronautical terms such that the x-axis is
parallel to the direction of travel (threw the center of the fuselage), y-axis is adjacent to x-axis in the same
plane (threw the center of the wings) and z-axis is vertical. For the biasing connections the forward
biased end of each sensor is the front, right and up for x, y and z respectively as shown in Figure 3.
Figure 3: Sensor Orientation
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