ADIS16135SLASHPCBZ datasheet(12/20 Pages) AD

12 / 20 page

ADIS16135

Rev. 0 | Page 12 of 20

CALIBRATION

The ADIS16135 factory calibration produces correction

formulas for the gyroscope and programs them into the flash

memory. Table 19 contains a list of user control registers that

provide 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

Address

Description

GYRO_OFF2

0x08

Gyroscope bias

GYRO_OFF

0x0A

Gyroscope bias

GLOB_CMD

0x28

Bias correction command

MEMS

GYRO

FACTORY

CALIBRATION

AND

FILTERING

ADC

GYRO_OUT GYRO_OUT2

GYRO_OFF GYRO_OFF2

Figure 19. Gyroscope Bias Calibration User Controls

The factory calibration addresses initial and temperature

dependent bias errors in the gyroscopes, but some

environmental 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

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. Wait for a complete output data cycle to complete, which

includes the entire average and decimation time in

DEC_RATE.

2. Read the gyroscope’s output registers.

3. Multiply the measurement by −1 to change its polarity.

4. Write the final value into the offset registers.

5. Update the flash memory.

The Allan variance curve shown in Figure 7 provides a trade-off

between bias accuracy and averaging time. The DEC_RATE

the ABC function. Set DEC_RATE[7:0] = 0x10 (DIN = 0xA210),

which sets the decimation rate to 65,536 (216) and provides an

averaging time of 64 seconds (65,536 ÷ 1024 SPS) for this

function. Then, 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 ADIS16135 automatically updates the

flash memory. Once the ABC function starts, the SPI is not

active. The only way to interrupt it 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 0.005°/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

Description (Default = 0x0000)

[15:0]

Gyroscope offset correction; twos complement,

0.0125°/sec per LSB

Table 21. GYRO_OFF2 Bit Descriptions

Bits

Description (Default = 0x0000)

[15:0]

Gyroscope offset correction, finer resolution; uses

same format as GYRO_OUT2 (see Table 11)

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.

ADIS16135/PCBZ Datasheet(PDF) 12 Page - Analog Devices

ADIS16135/PCBZ Datasheet(HTML) 12 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL