ADIS16251(RevPrA) Просмотр технического описания (PDF) - Analog Devices

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ADIS16251
(Rev.:RevPrA)

Programmable Low Power Gyroscope

Analog Devices 

ADIS16251

CALIBRATION

The ADIS16251 is factory-calibrated for sensitivity and bias. It

also provides several user calibration functions for simplifying

field-level corrections. The calibration factors are stored in

nonvolatile memory and are applied using the following linear

calibration equation:

y = mx + b

Where :

y = Calibrated output data x = Pre - calibration data

m = Sensitivity scale factor b = Offset scale factor

There are three options for system-level calibrations of the bias

in the ADIS16251: 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 above equation and

require two steps:

(1) characterize the behavior of the ADIS16251 at predefined

critical operating conditions, and (2) use this characterization

data to calculate and load the appropriate adjustment factors

into the GYRO_OFF (“b”). The GYRO_SCALE (“m”) register

can also be adjusted to implement corrections in the sensitivity

scale factor through the system calibration process.

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

nonvolatile as well.

Table 9. GYRO_OFF Register Definition

Address Scale1

Default Format

0x11,

0x10

0.018315°/sec 0x0000 Twos

complement

1 Scale is the weight of each LSB.

Table 10. GYRO_OFF Bit Designations

Bit

Description

15:12 Not used

11:0 Data bits

Access

R/W

Table 11. GYRO_SCALE Register Definition

Address

Scale1

Default2 Format

0x13, 0x12 0.0488%

0x0800 Binary

Access

R/W

1 Scale is the weight of each LSB. 2 Equates to a scale factor of one..

Table 12. GYRO_SCALE Bit Designations

Bit

Description

15:12 Not used

11:0 Data bits

Refer to AN-879 for a detailed description of calibrating the

ADIS16251, and other MEMS gyroscopes.

Preliminary Technical Data

GLOBAL COMMANDS

The ADIS16251 provides 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 have a unique control bit assigned to

them in the COMMAND register and are initiated by writing a 1 to

its assigned bit.

The auto null function does two different 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

twos steps: (1) read GYRO_OUT and (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 ADIS16251’s digital processor into a re-

start sequence, effectively doing the same thing as the RST line.

Table 13. COMMAND Register Definition

Address

Default

Format

0x3F, 0x3E

N/A

N/A

Access

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

Rev. PrA | Page 14 of 20

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