Analog Devices EV-ADA4571RSDZ, Руководство пользователя

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EV-ADA4571RSDZ User Guide UG-1169
Rev. 0 | Page 7 of 9
Vsin vs. Vcos Plot
The Vsin vs Vcos graph shows the electrical angle from the
ADA4571 . However, there is more information shown in
Figure 10, such as the radius of the output values that can give
further diagnostic information to system. As long as the sensor
is fully saturated, or the applied magnetic field strength exceeds
25 kA/m, the radius value remains unchanged at a constant
temperature. As the AMR effect is smaller at high temperatures,
the radius value changes with respect to temperature. See the
ADA4571 data sheet for the temperature coefficient values for
the output amplitude for the V
SIN
and the V
COS
channels.
161
35
-010
Figure 10. Vsin vs Vcos Graph
Digital Inputs
To toggle two digital inputs on the ADA4571 , click the buttons
in the Digital Inputs pane (see Figure 11).
The Power Down Disabled button puts the ADA4571 in a low
power state by disabling the internal circuitry and placing the
outputs in a high impedance state. See the
ADA4571 data sheet
for full details on the power-down current of the device.
The Gain Control Disabled button puts the device in gain control
mode (see Figure 11). This mode alters the bridge supply voltage
based on the internal temperature value of the
ADA4571 .
Through gain control mode, the output amplitude temperature
coefficient of the
ADA4571 reduces. See the ADA4571 data sheet
for full details on output amplitude vs. temperature with the gain
control mode enabled and disabled.
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5-
0
1
1
Figure 11. Digital Inputs Pane
Offset Calibration
An offset calibration is required to maximize the accuracy of
the
ADA4571 . The V
SIN
and V
COS
channels have inherent voltage
offsets due to a resistor mismatch within the AMR sensor bridges.
See the
ADA4571 data sheet for full details on the offset voltage
ranges for the outputs.
There are a few methods that can null the offsets for the outputs.
The
ADA4571 GUI uses a maximum/minimum value to calculate
these offsets. To run an offset calibration, click Run Cal (see
Figure 12 ) . When Run Cal is clicked, rotate the magnetic stimulus
slowly through an entire mechanical rotation. This slow rotation
ensures that the maximum and minimum output voltages are
found for each channel.
The offset of each channel is calculated as the midpoint between
the maximum and mid values captured during the calibration
cycle. During normal operation, the offset value for each channel is
subtracted from the current value before calculating the magnetic
angle.
1
613
5-
0
12
Figure 12. Offset Calibration Pane