SILICON DESIGNS, INC
!
Accurate, Easy-to-Use Alternative to
Piezoresistive Accelerometers
!
Capacitive Micromachined
!
Nitrogen Damped
!
±4V Differential Output or
0.5V to 4.5V Single Ended Output
!
Fully Calibrated
!
Low Power Consumption
!
-55 to +85EC Operation
E
!
+8 to +32V DC Power
!
Simple Four Wire Connection
!
Low Impedance Outputs Will Drive
Up To 15 Meters of Cable
!
Responds to DC and AC Acceleration
!
Non Standard g Ranges Available
!
Rugged Anodized Aluminum Module
!
Low Noise
!
Serialized for Traceability
P-Cap
TM
Model 2260
ANALOG ACCELEROMETER MODULE
ORDERING INFORMATION
Full Scale
Acceleration
± 2g
± 5g
± 10 g
± 25 g
± 50 g
±100 g
±200 g
Model
Number
2260-002
2260-005
2260-010
2260-025
2260-050
2260-100
2260-200
DESCRIPTION
The P-Cap
TM
model 2260 accelerometer module combines an integrated model 1221L accelerometer with high drive,
low impedance buffering for measuring acceleration in commercial/industrial environments. It is tailored for zero to
medium frequency instrumentation applications. The anodized aluminum case is epoxy sealed and is easily mounted
via two #4 (or M3) screws. On-board regulation is provided to minimize the effects of supply voltage variation. It is
relatively insensitive to temperature changes and thermal gradients. The cable’s shield is electrically connected to
the case while the ground (GND) wire is isolated from the case. An optional initial calibration sheet (2260-CAL) and
periodic calibration checking are also available.
OPERATION
The P-Cap
TM
Model 2260 accelerometer module produces two analog voltage outputs which vary with acceleration
as shown in the graph on the next page. The sensitive axis is perpendicular to the bottom of the package, with
positive acceleration defined as a force pushing on the bottom of the package. The signal outputs are fully differential
about a common mode voltage of approximately 2.5 volts. The output scale factor is independent from the supply
voltage of +8 to +32 volts. At zero acceleration the output differential voltage is nominally 0 volts DC; at ±full scale
acceleration the output differential voltage is ±4 volts DC respectively.
APPLICATIONS
!
FLIGHT TESTS
!
VIBRATION MONITORING
!
VIBRATION ANALYSIS
!
MACHINE CONTROL
P-Cap
is a trademark of Silicon Designs, Inc.
!
MODAL ANALYSIS
!
ROBOTICS
!
CRASH TESTING
!
INSTRUMENTATION
Silicon Designs, Inc.
!
1445-NW Mall Street, Issaquah, WA 98027-5344
!
Phone: 425-391-8329
!
Fax: 425-391-0446
web site:
www.silicondesigns.com
[page 1]
Apr 07
P-Cap
TM
Model 2260
Analog Accelerometer Module
SIGNAL DESCRIPTIONS
Vs and GND (Power):
Red and Black wires respectively. Power
(+9 to +32 Volts DC) and ground.
AOP and AON (Output):
Green and White wires respectively.
Analog output voltages proportional to acceleration; AOP voltage
increases (AON decreases) with positive acceleration. At zero
acceleration both outputs are nominally equal to 2.5 volts. The
device experiences positive (+1g) acceleration with its lid facing
up in the Earth’s gravitational field. Either output can be used
individually or the two outputs can be used differentially. (See
output response plot below)
PERFORMANCE
- By Model:
V
S
=+8 to +32VDC, T
C
=25EC
MODEL NUMBER
Input Range
Frequency Response
(Nominal, 3 dB)
Sensitivity, Differential
2
1
2260-002 2260-005 2260-010 2260-025 2260-050 2260-100 2260-200
±2
0 - 400
2000
13
±5
0 - 600
800
32
±10
400
63
±25
160
158
2000
Note 2: Single ended sensitivity is half of values shown.
±50
80
316
±100
40
632
±200
20
1265
0 - 1000 0 - 1500 0 - 2000 0 - 2500 0 - 2500
UNITS
g
Hz
mV/g
µg/(root
Hz)
g
Output Noise, Differential
(RMS, typical)
Max. Mechanical Shock
(0.1 ms)
Note 1: 250Hz ±100Hz, -3dB bandwidth, optionally available.
PERFORMANCE
- All Models:
Unless otherwise specified,
Vs=+8
to +32VDC, T
C
=25EC, Differential Mode.
PARAMETER
Cross Axis Sensitivity
Bias Calibration Error
Bias Temperature Shift
(T
C
= -40 to +80EC)
Scale Factor Calibration Error
3
MIN
-002
-005 thru -200
-002 & -005
-010 thru -200
-250
TYP
2
2
2
100
50
2
MAX
3
4
3
300
200
3
+250
0.5
1.0
1.5
UNITS
%
% of span
(ppm of span)/EC
%
ppm/EC
% of span
dB
VDC
VDC
mA DC
grams
grams/meter
Scale Factor Temperature Shift
(T
C
= -40 to +80EC)
Non-Linearity
(-90 to +90% of Full Scale)
3, 4
-002 thru -050
-100
-200
50
Power Supply Rejection Ratio
Output Impedance
Output Common Mode Voltage
Operating Voltage
Operating Current
(AOP & AON open)
Mass
(not including cable)
Cable Mass
Note 3: 100g versions and above are tested from -65g to +65g.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
0.15
0.25
0.40
>65
1
2.5
9
6
14
8
32
12
Note 4: Tighter tolerances available upon request.
P-cap
IS A REGISTERED TRADEMARK OF SILICON DESIGNS, INC.
Silicon Designs, Inc.
!
1445-NW Mall Street, Issaquah, WA 98027-5344
!
Phone: 425-391-8329
!
Fax: 425-391-0446
web site:
www.silicondesigns.com
[page 2]
Apr 07
P-Cap
TM
Model 2260
Analog Accelerometer Module
CABLE SPECIFICATIONS & LENGTH CONSIDERATIONS
The cable consists of four 28 AWG (7x36) silver plated copper wires with PTFE insulation surrounded by a braided shield. The
shield jacket is a PTFE tape wrap with a nominal outer diameter of 0.096”. Cable lengths of up to 15 meters (50 feet) can be
added to the model 2260's standard 1 meter cable without the need to test for output instability. For lengths longer than 15
meters we recommend you check each individual installation for oscillation by tapping the accelerometer and watching the
differential output for oscillation in the 20kHz to 50kHz region. If no oscillation is present then the cable length being used is OK.
From the standpoint of output current drive and slew rate limitations, the model 2260 is capable of driving over 600 meters (2000
feet) of its cable type but at some length between 15 and 600 meters, each device will likely begin to exhibit oscillation.
CONVERTING THE 2260's DIFFERENTIAL OUTPUT TO SINGLE ENDED
C1 = C2 (See below for value calculation)
R1, R2, R3 & R4 = 20k to 50k
R1 = R3 to within 0.1% for good common mode rejection
R2 = R4 to within 0.1% for good common mode rejection
R2 / R1 ratio accurate to within 0.1% for gain control
R4 / R3 ratio accurate to within 0.1% for gain control
To achieve the highest resolution and lowest noise performance from your model 2260 accelerometer module, it should
be connected to your voltage measurement instrument in a differential configuration using both the
AOP
and
AON
output
signals. If your measurement instrument lacks differential input capability or you desire to use a differential input capable
instrument in single ended mode, then the circuit above can be used to preserve the low noise performance of the model
2260 while using a single ended type connection.
This circuit converts the ± 4 Volt differential output of the model 2260 accelerometer, centered at +2.5 Volts, to a single
ended output centered about ground (0.0 Volts). It provides the advantage of low common mode noise by preventing the
accelerometer’s ground current from causing an error in the voltage reading.
The op-amp should be located as close as possible to your voltage monitoring equipment so that the majority of the signal
path is differential. Any noise present along the differential path will affect both wires to the same degree and the op-amp
will reject this noise because it is a common mode signal. The op-amp type is not critical; a
µA741
or ¼ of a LM124 can
be used. Both plus and minus supplies are needed for the op-amp to accommodate the positive and negative swings of
the single ended output.
For this design, always set R
1
= R
3
, R
2
= R
4
and C
1
= C
2
. The gain of the circuit is then determined by the ratio R
2
/R
1
.
When R
1
= R
2
= R
3
= R
4
, the gain equals 1 and the output swing will be ± 4 Volts single ended with respect to ground. To
obtain a ± 5 Volt single ended output, set R
2
/R
1
= R
4
/R
3
= 5/4 = 1.25. The single ended output of the op-amp will be
centered at ground if R
2
and C
1
are tied to ground; using some other fixed voltage for this reference will shift the output.
The value of the optional capacitors C
1
and C
2
(C
1
= C
2
) can be selected to roll off the frequency response to the frequency
range of interest. The cutoff frequency
f
0
(-3 dB frequency) for this single order low pass filter is given by:
f
0
=
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
1
2
π
R
2
C
1
P-cap
IS A REGISTERED TRADEMARK OF SILICON DESIGNS, INC.
Silicon Designs, Inc.
!
1445-NW Mall Street, Issaquah, WA 98027-5344
!
Phone: 425-391-8329
!
Fax: 425-391-0446
web site:
www.silicondesigns.com
[page 3]
Apr 07
