2
PCB’s High Sensitivity DC accelerometers are designed
utilizing a MEMS
(Micro-Electro-Mechanical Systems)
silicon sensor approach. The micro machining design
process provides sensor design flexibility, reliability &
stability over time. Compared to standard strain gages,
silicon sensor accelerometers have a much higher gage
factor. The sensor element of the 3741 series features a
proof mass, ringframe, and an attachment system between
the two. These features are micromachined from the same
single-crystal silicon wafer. The sensor is connected as a
bridge element in the circuit. The electrical characteristics
of one portion of the bridge increases while the other
decreases, when exposed to acceleration. The sensor
element itself is kept small through the use of cutting edge
processes such as DRIE (Deep Reactive Ion Etching).
Ruggedness is enhanced through the use of mechanical
stops on the two outer wafers to restrict the travel of the
proofmass. Gas damping is used to mitigate high
frequency inputs.
An on board voltage regulator allows a
wide range in excitation voltage with low current draw.
The positive output signal line increases with acceleration
while the negative line decreases proportionally. The
output lines have a common mode voltage above circuit
ground.
Consult the individual accelerometer data sheet on how to
order the particular model most appropriate for your
application. Adhesive mounting plates and triaxial
mounting blocks are available. If you have any questions
or concerns regarding optional configurations, consult the
Vibration Division’s product catalog or contact a PCB
factory representative.
4.0 INSTALLATION OVERVIEW
PCB’s high sensitivity DC accelerometers are supplied
with a silicone jacketed, shielded, multi-conductor,
integral cable assembly. With each conductor being 30
AWG, Teflon coated. The supplied cable length for a
standard DC accelerometer is 10 ft. or 120 in. (~3 m).
Custom cable length requirements should be specified at
time of ordering. When applications involve very long
cable runs, the user is advised to take into consideration
the added resistance of the cable wires and additional
capacitance values, as this may affect the voltage available
at the accelerometers input voltage regulator. Ensure the
recommended torque is used for the supplied 4-40
mounting cap screws.
The high sensitivity DC accelerometer output signal is
considered a differential signal which should be routed to
a differential amplifier or bridge conditioner (see Fig. 6).
The bridge conditioner should supply a regulated dc
supply and have proper amplification features. Although a
simple unregulated DC voltage supply is an acceptable
condition for operation, bridge conditioning equipment
typically has ZMO adjustment capability and standard
connector accessories included which provide a “plug &
play” environment.
Excitation input and Voltage output wiring conform to the
following color coding practice.
+ Excitation input (red)
– excitation input (black),
+ signal output (yellow)
– signal output (white).
Multi-pin connectors:
For accelerometer versions with
detachable cabling, make connection by inserting the
sensor’s mating pins onto the cable connector’s mating
sockets. Then thread the connector into place by turning
the cable connector’s outer shell onto the accelerometer’s
electrical connector.
4.1 SCREW MOUNT
This mounting technique requires smooth, flat contact
surfaces for proper operation and is recommended for
permanent and/or secure installations. Screw mounting is
recommended when testing at high frequencies.
STEP 1:
First, prepare a smooth, flat mounting surface,
then drill and tap mounting holes for mounting as shown
in Figure 3 and in accordance with the enclosed
Installation Drawing
.
Figure 3.
Mounting Surface Preparation
