1010L-002 Datasheet, PDF (4/9 Pages) List of Unclassifed Manufacturers – DIGITAL ACCELEROMETER

Model 1010 Digital Accelerometer
USING THE COUNT (CNT) OUTPUT: Pulses from the CNT output are meant to be accumulated in a hardware counter. Each
pulse accumulation or sample, reflects the average acceleration (change in velocity) over that interval. The sample period or
“gate time” over which these pulses are accumulated determines both the bandwidth and quantization of the measurement.
Quantization (g' s) = ^{gSPAN • f SR}
fCLK
f _CNT
=
f
CLK



1
2
+
g _FORCE


g_SPAN 
g _FORCE
=

g_{SPAN }
f _CNT
f _CLK
−
21^{}
Where:
gSPAN = 2 * (full scale acceleration in g' s)
f _SR = CNT sample rate in Hertz
fCLK = accelerometer clock rate in Hertz
fCNT = CNT pulse rate in pulses / sec
g_FORCE = acceleration in gravity units
1 g = 9.8085 m / s2 or 32.180 ft / s2
The first equation above shows that as the
sample rate is reduced (i.e. a longer
sample period), the quantization becomes
finer but bandwidth is reduced.
Conversely, as the sample rate is
increased, quantization becomes coarser
but the bandwidth of the measurement is
increased. The second and third equations
show how the CNT pulse frequency
equates to the applied g-force. When
using a frequency counter to monitor the
CNT output pulse rate, a counter with a DC
coupled input must be used. The CNT
output is a return-to-zero signal whose duty
cycle varies from zero to fifty percent, from
minus full scale to positive full scale
acceleration. A frequency counter with an
AC coupled input will provide an erroneous
reading as the duty cycle varies
appreciably from fifty percent. The figure to
the left illustrates how the CNT and DIR
outputs vary as the accelerometer is
subjected to accelerations from minus full
scale (-FS) to plus full scale (+FS).
DEFLECTION VOLTAGE (DV) TEST INPUT: This test input applies an electrostatic
force to the sense element, simulating a positive acceleration. It has a nominal input
impedance of 32 kΩ and a nominal open circuit voltage of aV_DD. For best accuracy during
normal operation, this input should be left unconnected or connected to a voltage source
equal to a of the V_DD supply. The change in output pulse rate (∆f) is proportional to the
square of the difference between the voltage applied to the DV input (V_DV) and aV_DD. Only
positive shifts in the output pulse rate may be generated by applying voltage to the DV
input. When voltage is applied to the DV input, it should be applied gradually. The
application of DV voltages greater than required to bring the output to positive full scale
may cause device damage. The proportionality constant (k) varies for each device and is
not characterized.
∆f
≈
k ^{}V_DV
−
1
3^VDD

2
ESD and LATCH-UP CONSIDERATIONS: The model 1010 accelerometer is a CMOS device subject to damage from large
electrostatic discharges. Diode protection is provided on the inputs and outputs but care should be exercised during handling
to assure that the device is placed only on a grounded conductive surface. Individuals and tools should be grounded before
coming in contact with the device. Do not insert the model 1010 into (or remove it from) a powered socket.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. ! 1445 NW Mall Street, Issaquah, WA 98027-5344 ! Phone: [phone] ! Fax: [phone]
web site: www.silicondesigns.com
[page 4]
Mar 07