2240-002 Datasheet, PDF (3/3 Pages) List of Unclassifed Manufacturers – ANALOG ACCELEROMETER MODULE

Model 2240 Analog Accelerometer Module
CABLE SPECIFICATIONS & LENGTH CONSIDERATIONS
The cable consists of four 30 AWG (7x38) silver plated copper wires with PTFE insulation surrounded by a braided shield. The
black FEP shield jacket has a nominal outer diameter of 0.100”. Cable lengths of up to 50 feet (15 meters) can be added to the
model 2240's standard 4 foot cable without the need to test for output instability. For lengths longer than 50 feet, 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 2240 is capable of driving over 2000 feet (600 meters) of its cable type
but at some length between 50 and 2000 feet, each device will likely begin to exhibit oscillation.
CONVERTING THE 2240's DIFFERENTIAL OUTPUT TO SINGLE ENDED
C1 = C2 (See below for value calculation)
R1, R2, R3 & R4 = 20kΩ to 50kΩ
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 2240 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
2240 while using a single ended type connection.
This circuit converts the ± 4 Volt differential output of the model 2240 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 R₁ = R₃, R₂ = R₄ and C₁ = C₂. The gain of the circuit is then determined by the ratio R₂/R₁.
When R₁ = R₂ = R₃ = R₄, 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 R₂/R₁ = R₄/R₃ = 5/4 = 1.25. The single ended output of the op-amp will be
centered at ground if R₂ and C₁ are tied to ground; using some other fixed voltage for this reference will shift the output.
The value of the optional capacitors C₁ and C₂ (C₁ = C₂) can be selected to roll off the frequency response to the frequency
range of interest. The cutoff frequency f₀ (-3 dB frequency) for this single order low pass filter is given by:
1
f ₀ = _{2π R2C1}
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
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Feb 08