參數(shù)資料
型號: ADXL250AQC
廠商: ANALOG DEVICES INC
元件分類: 模擬信號調理
英文描述: Top Entry Connector Hood; Enclosure Material:Aluminum Alloy; For Use With:C146 Rectangular Circular Connectors; Thread Size:PG 21; Connecting Termination:Screw; Gender:Male; No. of Contacts:24; Operating Voltage:400V; Series:C-146 RoHS Compliant: Yes
中文描述: SPECIALTY ANALOG CIRCUIT, CDSO14
封裝: CERPACK-14
文件頁數(shù): 9/15頁
文件大?。?/td> 341K
代理商: ADXL250AQC
ADXL150/ADXL250
–9–
REV. 0
R3
100k
V
R2 (SEE NOTES)
+V
S
OR GND
+V
S
R1
V
OUT
+V
S
2
SELF-TEST
+V
S
2
25k
V
5k
V
ADXL150
GAIN
AMP
OFFSET
NULL
COM
BUFFER
AMP
DEMODULATOR
SENSOR
+V
S
TP
(DO NOT CONNECT)
14
9
10
7
5
CLOCK
OP196
3
4
6
2
8
7
NOTES:
0g“QUICK” CALIBRATION METHOD USING RESISTOR R2 AND A +5V SUPPLY.
(a) WITH ACCELEROMETER ORIENTED AWAY FROM EARTH’S
GRAVITY (i.e., SIDEWAYS), MEASURE PIN 10 OF THE ADXL150.
(b) CALCULATE THE OFFSET VOLTAGE THAT NEEDS TO BE NULLED:
V
OS
=(+2.5V – V
PIN
10)(R3/R1).
OS
(d) FOR V
PIN
10 > +2.5V, R2 CONNECTS TO GND.
(e) FOR V
PIN
10 < +2.5V, R2 CONNECTS TO +V
S
.
(c) R2 = 2.V
EXT
AMP
GAIN
R1
VALUE
FS
RANGE
DESIRED
OUTPUT
SCALE FACTOR
76mV/g
100mV/g
200mV/g
400mV/g
6
25g
6
20g
6
10g
6
5g
2.0
2.6
5.3
10.5
49.9k
V
38.3k
V
18.7k
V
9.53k
V
C2
0.1
m
F
C1
0.1
m
F
C4
0.1
m
F
Figure 17. “Quick Zero g Calibration” Connection
Adjusting the Zero
g
Bias Level
When a true dc (gravity) response is needed, the output from
the accelerometer
must be
dc coupled
to the external amplifier’s
input. For high gain applications, a zero
g
offset trim will also be
needed. The external offset trim permits the user to set the zero
g
offset voltage to exactly +2.5 volts (allowing the maximum output
swing from the external amplifier without clipping with a +5
supply).
With a dc coupled connection, any difference between the zero
g
output and +2.5 V will be amplified along with the signal. To
obtain the exact zero
g
output desired or to allow the maximum
output voltage swing from the external amplifier, the zero
g
offset
will need to be externally trimmed using the circuit of Figure 20.
The external amplifier’s maximum output swing should be
limited to
±
2 volts, which provides a safety margin of
±
0.25
volts before clipping. With a +2.5 volt zero
g
level, the maxi-
mum gain will equal:
2
Volts
38
mV
/
g Times the Max Applied Acceleration in g
The device scale factor and zero
g
offset levels can be calibrated
using the earth’s gravity, as explained in the section “calibrating
the ADXL150/ADXL250.”
Using the Zero
g
“Quick-Cal” Method
In Figure 18 (accelerometer alone, no external op amp), a trim
potentiometer connects directly to the accelerometer’s zero
g
null pin. The “quick offset calibration” scheme shown in Figure
17 is preferred over using a potentiometer, which could change
its setting over time due to vibration. The “quick offset calibra-
tion” method requires measuring only the output voltage of
the ADXL150/ADXL250 while it is oriented normal to the
earth’s gravity. Then, by using the simple equations shown in
the figures, the correct resistance value for R2 can be calculated.
In Figure 17, an external op amp is used to amplify the signal. A
resistor, R2, is connected to the op amp’s summing junction.
The other side of R2 connects to either ground or +V
S
depend-
ing on which direction the offset needs to be shifted.
OFFSET
NULL
+V
S
200k
V
R
IN
AT PIN 8
30k
V
6
10k
V
SELF-TEST
+V
S
2
25k
V
5k
V
ADXL150
GAIN
AMP
COM
BUFFER
AMP
DEMODULATOR
SENSOR
+V
S
TP
(DO NOT CONNECT)
V
OUT
14
8
9
10
7
5
CLOCK
C1
0.1
m
F
C2
0.1
m
F
Figure 18. Offset Nulling the ADXL150/ADXL250 Using a Trim Potentiometer
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