It is anticipated that the EX-380 Series will
find applications where performance in severe
mechanical environments is equally important
to electrical performance. An additional focus
for the EX-380 series, therefore, was to
provide robust construction to withstand high
shock and vibration and to yield good
G-sensitivity performance. For example, when
the physical orientation of an oscillator is
changed, there is a small frequency change
(typically not more than several parts in 10-9
for a 90-degree rotation) due to change in
stress on the crystal blank resulting from the
gravitational effect upon the crystal supports.
This characteristic is known as "tip-over" and
is expressed in 10-9/g where one g represents
one-half of a 180-degree orientation change.
To minimize this change and also to enhance
performance under shock and vibration, the
crystal blank is mounted in a symmetrical
mounting structure, instead of the more
traditional 2 or 3 points. This helps to achieve
a high shock and vibration endurance level,
l o w
g - s e n s i t i v i t y p e r f o r m a n c e a n d
symmetrical heat transfer. Also, when a
crystal oscillator is operating and subjected to
vibration, spurious frequencies are generated,
offset from the frequency of oscillation by the
frequency of vibration. These are commonly
referred to as "vibration induced side-bands"
and these side-bands behave similarly to
phase noise. The amplitude of these spurious
outputs is related to the amplitude of vibration,
the mechanical design of the crystal supports,
and the mechanical design of the oscillator
assembly, including the crystal mounting. Here
also the symmetrical crystal mounting
structure helps to reduce unwanted noise.
Both AT and doubly rotated crystals can be
used in the EX-380 Series. Even though
many types of doubly rotated crystals
produce lower amplitude spurii under vibration
than the AT, this characteristic is primarily
determined by the mechanical design of the
crystal and oscillator rather than the specific
crystal cut. In many applications, Vectron uses
doubly rotated resonators in the oscillator to
provide lower close in phase noise, better
aging rates and reduced acceleration
sensitivity. In less critical applications, less
expensive AT cut crystals are used.
The following figures represent the typical
actual test data on qual samples for various
characteristics.
Figure 4
Frequency vs Temperature
Characteristics EX-380
SERIES @ 10 MHz
(Typical)
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