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參數(shù)資料
| 型號： | MXA2312A |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Low Cost, +2,-2 g Dual Axis Accelerometer with Analog Outputs |
| 中文描述： | 低成本，2，-2克雙軸加速度計的模擬輸出 |
| 文件頁數(shù)： | 7/8頁 |
| 文件大?。?/td> | 375K |
| 代理商： | MXA2312A |
Figure 6: Amplitude Frequency Response
COMPENSATION FOR ZERO
G
OFFSET CHANGE
OVER TEMPERATURE
In applications where a stable zero
g
offset is required, and
where the AC coupling external filter described earlier can
not be used, analog or digital temperature compensation
can be applied. The compensation requires individual
calibration because the magnitude of the zero
g
offset
change over temperature is different for each unit. To
compensate the change, a calibrated temperature dependent
signal equal in magnitude but with opposite polarity is
added to the accelerometer output. The circuit in Figure 7
shows a circuit example applying an analog linear
compensation technique. In this circuit the accelerometer
temperature sensor output is added to or subtracted from
the accelerometer output. The calibration sequence is: start
at room temperature with the 100K pot set so that its wiper
is at
V
ref
. Next, soak the accelerometer at the expected
extreme temperature and observe the direction of the
change. Then set the switch to the non-inverting input if the
change is negative or vice versa. Finally, adjust the 100K
pot while monitoring the circuit output, until the zero g
offset change is removed.
MEMSIC MXA2312A Rev .E
Page 7 of
8
5/15/2004
+5V
-
+
100K
SW SPDT
100K
100K
100K
10K
10K
Tout
Vref
10K
Aoutx or y
zero g drift
compensated
100K
Aoutx or y
100K
Figure 7: Zero g Offset Temperature Compensation Circuit
Various digital compensation techniques can be applied
using a similar concept. Digital techniques can provide
better compensation because they can compensate for non-
linear zero
g
offset vs. temperature. A micro-controller or
micro-processor would perform the compensation. The
acceleration signal and the temperature signal would be
digitized using an analog to digital converter. Like in the
analog compensation, the first step is to test and
characterize the zero g change. The purpose of the
characterization is to create a look up table or to estimate a
mathematical representation of the change. For example,
the change could be characterized by an equation of the
form:
Change = a * Temperature
2
+ b * Temperature + c
where
a,b,c
are unique constants for each accelerometer.
In normal operation the processor calculates the output:
Compensated Output = Acceleration – Change.
For a more detail discussion of temperature compensation
reference MEMSIC application note #AN-00MX-002.
TEMPERATURE OUTPUT NOISE REDUCTION
It is recommended that a simple RC low pass filter is used
when measuring the temperature output. Temperature
output is typically a very slow changing signal, so a very
low frequency filter eliminates erroneous readings that may
result from the presence of higher frequency noise. A
simple filter is shown in Figure 8.
-60
-45
-30
-15
0
15
30
45
60
10
100
1000
Frequency - Hz
A
Filtered TOUT
8.2K
0.1uF
MEMSIC
Accel.
TOUT
Figure 8: Temperature Output Noise Reduction
POWER SUPPLY NOISE REJECTION
Two capacitors and a resistor are recommended for best
rejection of power supply noise (reference Figure 9 below).
The capacitors should be located as close as possible to the
device supply pins (V
DA
, V
DD
). The capacitor lead length
should be as short as possible, and surface mount capacitors
are preferred. For typical applications, capacitors C1 and
C2 can be ceramic 0.1 μF, and the resistor R can be 10
.
In 5V applications where power consumption is not a
concern, maximum supply noise rejection can be obtained
by significantly increasing the values of C1, C2 and R. For
example, C1 = C2 = 0.47 μF and R = 270
will virtually
eliminate power supply noise effects.
R
MEMSIC
Accelerometer
VDA
C1
C2
VDD
V SUPPLY
Figure 9: Power Supply Noise Rejection
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