ADIS16136/PCBZ AD [Analog Devices], ADIS16136/PCBZ Datasheet - Page 13

• Manufacturer Part Number: ADIS16136/PCBZ
• Manufacturer: AD [Analog Devices]

Data Sheet
CALIBRATION
The
formulas for the gyroscope and programs them into the flash
memory. Table 19 contains a list of user control registers that
provide an opportunity for user optimization after installation.
Figure 19 illustrates the summing function of the sensor’s offset
correction register.
Table 19. Registers for User Calibration
Register
GYRO_OFF2
GYRO_OFF
GLOB_CMD
The factory calibration addresses initial and temperature
dependent bias errors in the gyroscopes, but some environ-
mental conditions, such as temperature cycling and mechanical
stress on the package, can cause bias shifts in MEMS gyroscope
structures. For systems that value absolute bias accuracy, there
are two options for optimizing absolute bias accuracy: autonull
and manual correction.
AUTOMATIC BIAS CORRECTION (AUTONULL)
Set GLOB_CMD[0] = 1 (DIN = 0xA801) to start the automatic
bias correction (ABC) function, which uses the following
internal sequence to calibrate each gyroscope for bias error:
1.
2.
3.
4.
5.
MEMS
GYRO
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Wait for a complete output data cycle to complete, which
includes the entire average and decimation time in
DEC_RATE.
Read the output registers of the gyroscope.
Multiply the measurement by −1 to change its polarity.
Write the final value into the offset registers.
Update the flash memory.
Figure 19. Gyroscope Bias Calibration User Controls
ADC
factory calibration produces correction
Address
0x08
0x0A
0x28
CALIBRATION
FILTERING
FACTORY
AND
GYRO_OFF GYRO_OFF2
Description
Gyroscope bias
Gyroscope bias
Bias correction command
GYRO_OUT GYRO_OUT2
Rev. A | Page 13 of 20
The Allan variance curve shown in Figure 7 provides a trade-off
between bias accuracy and averaging time. The DEC_RATE
register provides a user control for averaging time when using
the ABC function. Set DEC_RATE[7:0] = 0x10 (DIN = 0xA210),
which sets the decimation rate to 65,536 (2
averaging time of 64 seconds (65,536 ÷ 1024 SPS) for this function.
Next, set GLOB_CMD[0] = 1 (DIN = 0xA801), and keep the
platform stable for at least 65 seconds while the gyroscope bias
data accumulates.
After this completes, the
flash memory. When the ABC function starts, the SPI is not active.
The only way to interrupt the ABC function is to remove power
or initiate a hardware reset using the RST pin. When using
DEC_RATE = 0x0010, the 1 σ accuracy for this correction is
approximately 0.001°/sec for the gyroscope correction factor.
See Table 29 for more information on GLOB_CMD.
MANUAL BIAS CORRECTION
The GYRO_OFF and GYRO_OFF2 registers (see Table 20 and
Table 21) provide a bias adjustment function for the output of
each sensor. GYRO_OFF has the same format as GYRO_OUT,
and GYRO_OFF2 has the same format as GYRO_OUT2.
Table 20. GYRO_OFF Bit Descriptions
Bits
[15:0]
Table 21. GYRO_OFF2 Bit Descriptions
Bits
[15:0]
Restoring Factory Calibration
Set GLOB_CMD[1] = 1 (DIN = 0xA802) to execute the factory
calibration restore function. This function resets each user
calibration register to 0x0000, resets all sensor data to 0, and
automatically updates the flash memory within 72 ms. See
Table 29 for more information on GLOB_CMD.
Description (Default = 0x0000)
Gyroscope offset correction; twos complement,
0.018275°/sec per LSB
Description (Default = 0x0000)
Gyroscope offset correction, finer resolution; uses
same format as GYRO_OUT2 (see Table 11)
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automatically updates the
16
) and provides an
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