EVAL-ADXL350Z-S Analog Devices, EVAL-ADXL350Z-S Datasheet - Page 30

• Manufacturer Part Number: EVAL-ADXL350Z-S
• Description: Daughter Cards & OEM Boards EB
• Manufacturer: Analog Devices
• Series: ADXL350r

Specifications of EVAL-ADXL350Z-S

• Rohs: yes
• Product: Satellite Boards
• Description/function: 3 axis accelerometer evaluation board
• Interface Type: I2C, SPI
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Operating Supply Voltage: 2 V to 3.6 V
• Factory Pack Quantity: 1
• For Use With: ADXL350

ADXL350
using the built-in offset registers. This results in the data acquired
from the DATA registers already compensating for any offset.
In a no-turn or single-point calibration scheme, the part is oriented
such that one axis, typically the z-axis, is in the 1 g field of gravity
and the remaining axes, typically the x-axis and y-axis, are in a
0 g field. The output is then measured by taking the average of a
series of samples. The number of samples averaged is a choice of
the system designer, but a recommended starting point is 0.1 sec
worth of data for data rates of 100 Hz or greater. This corresponds
to 10 samples at the 100 Hz data rate. For data rates less than
100 Hz, it is recommended that at least 10 samples be averaged
together. These values are stored as X
measurements on the x-axis and y-axis and the 1 g measure-
ment on the z-axis, respectively.
The values measured for X
offset, and compensation is done by subtracting those values from
the output of the accelerometer to obtain the actual acceleration.
Because the z-axis measurement was done in a +1 g field, a no-turn
or single-point calibration scheme assumes an ideal sensitivity,
S
offset, which is then subtracted from future measured values to
obtain the actual value:
The
by using the offset registers (Register 0x1E, Register 0x1F, and
Register 0x20). These registers contain an 8-bit, twos complement
value that is automatically added to all measured acceleration
values, and the result is then placed into the DATA registers.
Because the value placed in an offset register is additive, a negative
value is placed into the register to eliminate a positive offset and
vice versa for a negative offset. The register has a scale factor of
7.8 mg/LSB and is independent of the selected g-range.
As an example, assume that the
resolution mode with a sensitivity of typically 512 LSB/g. The
part is oriented such that the z-axis is in the field of gravity and
x-, y-, and z-axis outputs are measured as +10 LSB, −13 LSB,
and +9 LSB, respectively. Using the previous equations, X
+10 LSB, Y
in full-resolution is 1.95 mg or one-quarter of an LSB of the
offset register. Because the offset register is additive, the 0 g
values are negated and rounded to the nearest LSB of the offset
register:
These values are programmed into the OFSX, OFSY, and OFXZ
registers, respectively, as 0xFD, 0x03, and 0xFE. As with all
Z
for the z-axis. This is subtracted from Z
ADXL350
X
Y
Z
Z
X
Y
Z
ACTUAL
0g
ACTUAL
OFFSET
OFFSET
ACTUAL
OFFSET
= Z
0g
+1g
= −Round(9/4) = −2 LSB
= −Round(10/4) = −3 LSB
= −Round(−13/4) = 3 LSB
= Y
= Z
= X
is −13 LSB, and Z
− S
can automatically compensate the output for offset
MEAS
MEAS
MEAS
Z
− Z
− Y
− X
0g
0g
0g
0g
and Y
0g
ADXL350
is +9 LSB. Each LSB of output
0g
correspond to the x- and y-axis
0g
, Y
0g
+1g
is placed into full-
, and Z
to attain the z-axis
+1g
for the 0 g
0g
is
Rev. 0 | Page 30 of 36
registers in the ADXL350, the offset registers do not retain the
value written into them when power is removed from the part.
Power cycling the
default value of 0x00.
Because the no-turn or single-point calibration method assumes an
ideal sensitivity in the z-axis, any error in the sensitivity results in
offset error. To help minimize this error, an additional measure-
ment point can be used with the z-axis in a 0 g field and the 0 g
measurement can be used in the Z
USING SELF-TEST
The self-test change is defined as the difference between the
acceleration output of an axis with self-test enabled and the
acceleration output of the same axis with self-test disabled (see
Endnote 4 of Table 1). This definition assumes that the sensor
does not move between these two measurements, because if the
sensor moves, a non-self-test related shift corrupts the test.
Proper configuration of the
accurate self-test measurement. The part should be set with a
data rate that is greater than or equal to 100 Hz. This is done by
ensuring that a value greater than or equal to 0x0A is written
into the rate bits (Bit D3 through Bit D0) in the BW_RATE
register (Address 0x2C).
It is also recommended that the part be set to ±8 g mode to
ensure that there is sufficient dynamic range for the entire self-test
shift. This is done by setting Bit D3 of the DATA_FORMAT
register (Address 0x31) and writing a value of 0x03 to the range
bits (Bit D1 and Bit D0) of the DATA_FORMAT register (Address
0x31). This results in a high dynamic range for measurement and
a 2 mg/LSB scale factor.
After the part is configured for accurate self-test measurement,
several samples of x-, y-, and z-axis acceleration data should be
retrieved from the sensor and averaged together. The number of
samples averaged is a choice of the system designer, but a recom-
mended starting point is 0.1 sec worth of data, which corresponds
to 10 samples at 100 Hz data rate. The averaged values should
be stored and labeled appropriately as the self-test disabled data,
that is, X
Next, self-test should be enabled by setting Bit D7 of the
DATA_FORMAT register (Address 0x31). The output needs
some time (about four samples) to settle after enabling self-test.
After allowing the output to settle, several samples of the x-, y-,
and z-axis acceleration data should be taken again and averaged. It
is recommended that the same number of samples be taken for
this average as was previously taken. These averaged values should
again be stored and labeled appropriately as the value with self-
test enabled, that is, X
be disabled by clearing Bit D7 of the DATA_FORMAT register
(Address 0x31).
ST_OFF
, Y
ST_OFF
ADXL350
, and Z
ST_ON
, Y
ADXL350
ST_OFF
returns the offset registers to their
ST_ON
.
, and Z
ACTUAL
is also necessary for an
equation.
ST_ON
. Self-test can then
Data Sheet