Rainbow Electronics DAB-IMU-C01 - Manual (Page 14)

ADIS16250/ADIS16255
Rev. B | Page 14 of 20
CALIBRATION
The ADIS16250/ADIS16255 are factory-calibrated for
sensitivity and bias. It also provides several user calibration
functions for simplifying field-level corrections. The calibra-
tion factors are stored in nonvolatile memory and are applied
using the following linear calibration equation:
y = mx + b
where:
y is the calibrated output data.
x is the precalibration data.
m is the sensitivity scale factor.
b is the offset scale factor.
There are three options for system-level calibrations of the
bias in the ADIS16250/ADIS16255: auto-null, factory
calibration restore, and manual calibration updates. The
auto-null and factory reset options are described in the
Global Commands section. Optional field-level calibrations
use the preceding equation and require two steps:
1. Characterize the behavior of the ADIS16250/ADIS16255
at predefined critical operating conditions.
2. Use this characterization data to calculate and load the
contents of GYRO_OFF (b) and GYRO_SCALE (m).
The GYRO_OFF provides a calibration range of ±37.5°/sec,
and its contents are nonvolatile. The GYRO_SCALE register
provides a calibration range of 0 to 1.9995, and its contents
are also nonvolatile.
Table 9. GYRO_OFF Register Definition
Address Scale
1 Default Format Access
0x15,
0x14 0.018315°/sec 0x0000 Twos
complement
R/W
1 Scale is the weight of each LSB.
Table 10. GYRO_OFF Bit Descriptions
Bit Description
15:12 Not used
11:0 Data bits
Table 11. GYRO_SCALE Register Definition
Address Scale
1 Default 2 Format Access
0x17, 0x16 0.0487% 0x0800 Binary R/W
1 Scale is the weight of each LSB.
2 Equates to a scale factor of one.
Table 12. GYRO_SCALE Bit Descriptions
Bit Description
15:12 Not used
11:0 Data bits
GLOBAL COMMANDS
The ADIS16250/ADIS16255 provide global commands for
common operations such as auto-null, factory calibration restore,
manual flash update, auxiliary DAC latch, and software reset. Each
of these global commands has a unique control bit assigned to it in
the COMMAND register and is initiated by writing a 1 to its
assigned bit.
The auto-null function does two things: it resets the contents of the
ANGL_OUT register to zero, and it adjusts the GYRO_OUT
register to zero. This automated adjustment takes two steps:
1. Read GYRO_OUT.
2. Write the opposite of this value into the GRYO_OFF register.
Sensor noise influences the accuracy of this step.
For optimal calibration accuracy, set the number of filtering taps to
its maximum, wait for the appropriate number of samples to
process through the filter, and then exercise this option.
The factory calibration restore command sets the contents of
GYRO_OFF to 0x0000 and GYRO_SCALE to 0x0800, erasing any
field-level calibration contents. The manual flash update writes the
contents of each nonvolatile register into flash memory for storage.
This process takes approximately 50 ms and requires the power
supply voltage to be within specification for the duration of the
event. It is worth noting that this operation also automatically
follows the auto-null and factory reset commands.
The DAC latch command loads the contents of AUX_DAC into the
DAC latches. Since the AUX_DAC contents must be updated one
byte at a time, this command ensures a stable DAC output voltage
during updates. Finally, the software reset command sends the
ADIS16250/ADIS16255 digital processor into a restart sequence,
effectively doing the same thing as the RST line.
Table 13. COMMAND Register Definition
Address Default Format Access
0x3F, 0x3E N/A N/A Write only
Table 14. COMMAND Bit Descriptions
Bit Description
15:8 Not used
7 Software reset command
6:4 Not used
3 Manual flash update command
2 Auxiliary DAC data latch
1 Factory calibration restore command
0 Auto-null command
OPERATIONAL CONTROL
Internal Sample Rate
The internal sample rate defines how often data output variables
are updated, independent of the rate at which they are read out on
the SPI port. The SMPL_PRD register controls the ADIS16250/
ADIS16255 internal sample rate and has two parts: a selectable