WORLD’S SMALLEST IEPE
TRIAXIAL ACCELEROMETER
Size should be a crucial factor
when selecting an accelerometer
// ANTHONY CHU
Who, on Heaven’s green earth would
want to buy a triaxial accelerometer,
much less one that’s so small it can
hardly be seen?
It’s a good question from a
cost-conscious test professional that sees
the price of three single axis
accelerometers as less expensive than a
triaxial accelerometer and one who is
measuring vibration on large objects.
However, time is money and preparing a
single location for mounting one device
rather than three locations for three
devices makes sense.
Further, cable installation and
connecting to instrumentation is less
complicated and less time consuming for a
single location than three. From a
measurement perspective, taking data
from a single location allows test
professionals to preserve phase
information as well as to ensure the data is
not contaminated by structural differences
among locations.
MINIATURE AND LIGHTWEIGHT
Size is important for two reasons. First, it
avoids mass-loading effects where the mass
of the accelerometer on a small structure
alters the natural frequency of the
structure under test. Second, many
measurements have very demanding space
restrictions. Consequently, the ultraminiature,
lightweight footprint of
Endevco’s 35C makes it ideal for spacerestricted
testing applications, especially in
the aircraft, spacecraft, satellite, and
missile industries where more conventional
accelerometers cannot be used.
The 35C is an ultra-miniature, adhesive
mounted triaxial piezoelectric
accelerometer with integral electronics. Its
tiny size, 0.235in cube, and light weight,
0.76g (sensor only), makes it ideal for
measuring vibration on very small objects.
As a general rule, the accelerometer mass
should be no more than one tenth of the
dynamic mass of the vibrating part onto
which it is mounted.
All materials used for the Model 35C
construction have less than or equal to 1%
TML (Total Mass Loss) and a CVCM
(Collected Volatile Condensed Mass) less
than or equal to 0.1%, verified by NASA
documentation. The shear ferroelectric
crystal technology underlying the sensor
design provides very low sensitivity to base
strain, cable strain and very low thermal
transient response. This technology also
provides a wide-band frequency and
140 SHOWCASE 2020 \\ AEROSPACETESTINGINTERNATIONAL.COM
// The Endevco 35C
accelerometer is small
enough to be used instead
of three accelerometers
SENSORS
insensitivity to non-acceleration input in a
rugged and reliable package.
The 35C’s hermetically sealed titanium
case is well-suited for use in humid,
corrosive and dirty environments. Further,
its waterproof Ingress Protection Marking
(IP68) guarantees performance at 100
meters depth and 48 hours duration.
Mounting the accelerometer is easily
performed using Cyanoacrylate adhesives
while removal is achieved with the
appropriate solvent and the removal tool
supplied with each accelerometer.
PERFORMANCE
The 35C has an integral three-foot cable
that terminates to a single threaded ¼-28
4-pin connector. This accelerometer is
available in three sensitivities: 2.5 mV/g, 5
mV/g and 10 mV/g. It operates in annular
shear mode which exhibits excellent
output sensitivity stability over time. The
35C is also designed with a very low noise
floor that results in an outstanding signal
to noise ratio for more accurate
measurements.
The accelerometer incorporates an
internal hybrid signal conditioner in a twowire
system, which transmits its low
impedance voltage output through the
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