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ADXL50_15 Datasheet(Arkusz danych) 5 Page - Analog Devices
AD [Analog Devices]
Sensitivity: The output voltage change per g unit of accelera-
tion applied, specified at the V
pin in mV/g.
Sensitive Axis (X): The most sensitive axis of the accelerom-
eter sensor. Defined by a line drawn between the package tab
and Pin 5 in the plane of the pin circle. See Figures 2a and 2b.
Sensor Alignment Error: Misalignment between the
ADXL50’s on-chip sensor and the package axis, defined by
Pin 5 and the package tab.
Total Alignment Error: Net misalignment of the ADXL50’s
on-chip sensor and the measurement axis of the application.
This error includes errors due to sensor die alignment to the
package, and any misalignment due to installation of the sensor
package in a circuit board or module.
Transverse Acceleration: Any acceleration applied 90
° to the
axis of sensitivity.
Transverse Sensitivity Error: The percent of a transverse ac-
celeration that appears at the V
output. For example, if the
transverse sensitivity is 1%, then a +10 g transverse acceleration
will cause a 0.1 g signal to appear at V
(1% of 10 g). Trans-
verse sensitivity can result from a sensitivity of the sensor to
transverse forces or from misalignment of the internal sensor to
Transverse Y Axis: The axis perpendicular (90
°) to the pack-
age axis of sensitivity in the plane of the package pin circle. See
Transverse Z Axis: The axis perpendicular (90
°) to both the
package axis of sensitivity and the plane of the package pin
circle. See Figure 2.
Figure 3. 500 g Shock Overload Recovery. Top Trace:
ADXL50 Output. Bottom Trace: Reference Accelerometer
Table I shows the percentage signals resulting from various
angles. Note that small errors in alignment have a negligible
effect on the output signal. A 1
° error will only cause a 0.02%
error in the signal. Note, however, that a signal coming 1
° off of
the transverse axis (i.e., 89
° off the sensitive axis) will still con-
tribute 1.7% of its signal to the output. Thus large transverse
signals could cause output signals as large as the signals of
Table I may also be used to approximate the effect of the
ADXL50’s internal errors due to misalignment of the die to the
package. For example: a 1 degree sensor alignment error will
allow 1.7% of a transverse signal to appear at the output. In a
nonideal sensor, transverse sensitivity may also occur due to in-
herent sensor properties. That is, if the sensor physically moves
due to a force applied exactly 90
° to its sensitive axis, then this
might be detected as an output signal, whereas an ideal sensor
would reject such signals. In every day use, alignment errors
may cause a small output peak with accelerations applied close
to the sensitive axis but the largest errors are normally due to
large accelerations applied close to the transverse axis.
Errors Due to Mounting Fixture Resonances
A common source of error in acceleration sensing is resonance
of the mounting fixture. For example, the circuit board that the
ADXL50 mounts to may have resonant frequencies in the same
range as the signals of interest. This could cause the signals
measured to be larger than they really are. A common solution
to this problem is to dampen these resonances by mounting the
ADXL50 near a mounting post or by adding extra screws to
hold the board more securely in place.
When testing the accelerometer in your end application, it is
recommended that you test the application at a variety of fre-
quencies in order to ensure that no major resonance problems
GLOSSARY OF TERMS
Acceleration: Change in velocity per unit time.
Acceleration Vector: Vector describing the net acceleration
acting upon the ADXL50 (A
g: A unit of acceleration equal to the average force of gravity
occurring at the earth’s surface. A g is approximately equal to
, or 9.807 meters/s
Nonlinearity: The maximum deviation of the ADXL50 output
voltage from a best fit straight line fitted to a plot of acceleration
vs. output voltage, calculated as a % of the full-scale output
voltage (@ 50 g).
Resonant Frequency: The natural frequency of vibration of
the ADXL50 sensor’s central plate (or “beam”). At its resonant
frequency of 24 kHz, the ADXL50’s moving center plate has a
peak in its frequency response with a Q of 3 or 4.
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