4
System Details
4.1
Sensor
The X16-5 uses the Analog Devices ADXL345 3-axis digital accelerometer sensor, which is based on
micro-electro machined semiconductor technology (MEMS). This accelerometer sensor is similar to
those used in cellphones, laptops, hard drives and other consumer electronics. Appendix 6.1 describes
how a MEMS accelerometer sensor works. Table 3 lists the basic sensor and logger performance
parameters but refer to Analog Devices for detailed sensor specifications.
Table 3: Accelerometer Sensor Characteristics
Parameter
Condition
Min
Typical
Max
Units
Acceleration range
±16.0
g
Sensitivity
2048
count/g
Sensitivity Deviation
±1.0
%
Nonlinearity
X, Y, Z axis
±0.5
%FS
Zero-g Offset Level
Accuracy
X, Y axis
-150
+150
mg
Z axis
-250
+250
mg
Inter-Axis Alignment Error
±0.1
Degrees
Cross-Axis Sensitivity
±1
%
The ADXL345 accelerometer sensor “pushes” data to the logger at selected rates based on a clock
internal to the sensor. The sensor's clock precision and drift are undefined. For example, a selected
sample rate of 50 Hz may actually push data at 52 Hz. The X16-5 incorporates a precise real time clock
to independently time stamp the data as it leaves the sensor and to ensure that accurate timing is
recorded to the data file. Therefore, the time stamps should be used as the reference for determining
the actual sample rates.
Gulf Coast Data Concepts
Page 19
X16-5, Rev New
The accelerometer sensor is based on microelectromechanical systems (MEMS)
technology and is not affected by magnetic fields. Glue a magnet to the bottom of the
plastic enclosure to facilitate easy attachment to iron surfaces.
The MEMS accelerometer sensor will detect the acceleration of gravity, which is a
convenient feature for validating the sensor operation. Setting the logger on a flat level
surface will result in -2048 counts (-1g) in the z-axis.
