2010-002 Datasheet, PDF (3/3 Pages) List of Unclassifed Manufacturers – DIGITAL ACCELEROMETER MODULE

Model 2010 Digital Accelerometer Module
SIGNAL DESCRIPTIONS
CLK (input): Reference clock input. This hysteresis threshold input must be driven by a 50% duty cycle square wave
signal. Factory Calibration is performed at 250 kHz but the 2210 will operate at frequencies as low as 100 kHz or as
high as 1 MHz.
CNT (output): Count output. A return-to-zero type digital pulse stream whose pulse width is equal to the input CLK logic
high time. The CNT pulse rate increases with positive acceleration. The device experiences positive (+1g)
acceleration with its lid facing up in the earth’s gravitational field. This signal is meant to drive an up-counter directly.
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) =
g_SPAN • f _SR
fCLK
f _CNT
=
f
CLK



1
2
+
g _FORCE


g_SPAN 
g _FORCE
=

g
SPAN


f _CNT
f _CLK
−
1
2
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 = 9.807 m / s2 or 32.175ft / 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.
CABLE LENGTH CONSIDERATIONS
Cable lengths of up to 45 meters (150 feet) can be added to the model 2010's standard 1 meter cable when it is connected
to a Model 3901 Adapter Cable and is being used with a Model 3320 G-LOGGER_TM. The extension cable must however,
be a longer version of the G-LOGGER_TM 9 conductor flat cable instead of the 2010's round cable to reduce crosstalk
between the CNT and CLK signals. 15 meter (50 foot) cable lengths of DB9 male to DB9 female flat extension cable are
available on special order.
Silicon Designs, Inc. ! 1445-NW Mall Street, Issaquah, WA 98027-5344 ! Phone: [phone] ! Fax: [phone]
web site: www.silicondesigns.com
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Sep 07