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參數(shù)資料
| 型號： | MXA2500U |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Ultra Low Noise, 1g Dual Axis Accelerometer with Analog Outputs |
| 中文描述： | 超低噪音，1克雙軸加速度計的模擬輸出 |
| 文件頁數(shù)： | 5/8頁 |
| 文件大?。?/td> | 321K |
| 代理商： | MXA2500U |
or software. Any compensation for this effect could be
done instinctively by the game player.
For applications where sensitivity changes of a few percent
are acceptable, the above equation can be approximated
with a linear function. Using a linear approximation, an
external circuit that provides a gain adjustment of –0.9%/
°
C
would keep the sensitivity within 10% of its room
temperature value over a 0
°
C to +50
°
C range.
For applications that demand high performance, a low cost
micro-controller can be used to implement the above
equation. A reference design using a Microchip MCU (p/n
16F873/04-SO) and MEMSIC developed firmware is
available by contacting the factory. With this reference
design, the sensitivity variation over the full temperature
range (-40
°
C to +105
°
C) can be kept below 3%. Please
visit the MEMSIC web site at
www.memsic.com
for
reference design information on circuits and programs
including look up tables for easily incorporating sensitivity
compensation.
DISCUSSION OF TILT APPLICATIONS AND
RESOLUTION
Tilt Applications:
One of the most popular applications of
the MEMSIC accelerometer product line is in
tilt/inclination measurement. An accelerometer uses the
force of gravity as an input to determine the inclination
angle of an object.
A MEMSIC accelerometer is most sensitive to changes in
position, or tilt, when the accelerometer’s sensitive axis is
perpendicular to the force of gravity, or parallel to the
Earth’s surface. Similarly, when the accelerometer’s axis is
parallel to the force of gravity (perpendicular to the Earth’s
surface), it is least sensitive to changes in tilt.
Table 1 and Figure 2 help illustrate the output changes in
the X- and Y-axes as the unit is tilted from +90
°
to 0
°
.
Notice that when one axis has a small change in output per
degree of tilt (in m
g
), the second axis has a large change in
output per degree of tilt. The complementary nature of
these two signals permits low cost accurate tilt sensing to
be achieved with the MEMSIC device (reference
application note AN-00MX-007).
X
MEMSIC MXA2500U Rev A
Page 5 of
8
05/02
Top View
Y
+90
0
0
0
gravity
M
Figure 2: Accelerometer Position Relative to Gravity
X-Axis
Orientatio
n
To Earth’s
Surface
(deg.)
90
85
80
70
60
45
30
20
10
5
0
X-Axis
Y-Axis
X Output
(
g
)
Change
per deg.
of tilt
(m
g
)
Y Output
(
g
)
Change
per deg.
of tilt
(m
g
)
1.000
0.996
0.985
0.940
0.866
0.707
0.500
0.342
0.174
0.087
0.000
12.23
15.04
16.35
17.16
17.37
17.45
0.15
1.37
2.88
5.86
8.59
0.000
0.087
0.174
0.342
0.500
0.707
0.866
0.940
0.985
0.996
1.000
17.45
17.37
17.16
16.35
15.04
12.23
8.59
5.86
2.88
1.37
0.15
Table 1: Changes in Tilt for X- and Y-Axes
Resolution
: The accelerometer resolution is limited by
noise. The output noise will vary with the measurement
bandwidth. With the reduction of the bandwidth, by
applying an external low pass filter, the output noise drops.
Reduction of bandwidth will improve the signal to noise
ratio and the resolution. The output noise scales directly
with the square root of the measurement bandwidth. The
maximum amplitude of the noise, its peak- to- peak value,
approximately defines the worst case resolution of the
measurement. With a simple RC low pass filter, the rms
noise is calculated as follows:
Noise (mg rms) = Noise(mg/
Hz
) *
The peak-to-peak noise is approximately equal to 6.6 times
the rms value (for an average uncertainty of 0.1%).
EXTERNAL FILTERS
AC Coupling
: For applications where only dynamic
accelerations (vibration) are to be measured, it is
recommended to ac couple the accelerometer output as
shown in Figure 3. The advantage of ac coupling is that
variations from part to part of zero
g
offset and zero
g
offset versus temperature can be eliminated. Figure 3 is a
HPF (high pass filter) with a –3dB breakpoint given by the
equation:
RC
π
2
desirable to have the HPF –3dB point at a very low
frequency in order to detect very low frequency
accelerations. Sometimes the implementation of this HPF
may result in unreasonably large capacitors, and the
designer must turn to digital implementations of HPFs
where very low frequency –3dB breakpoints can be
achieved.
)
*
)
(
(
Hz
Bandwidth
f
1
=
. In many applications it may be
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