bridge circuit to sense acceleration and this is how they work.

    The mass is seeing the one G acceleration force due to gavity
    and is deflected downward. That means the spacing between the plates
    of C1 gets larger and the spacing of C2 gets smaller.

    As the spacing of the plates of a capacitor get larger
    the capacitance is reduced. When the spacing gets smaller
    the capacitance is increased.

    Think of a capacitor as a variable resisters for waves.

    There is an oscillator that supplies a constant amplitude  sine wave
to the
    device.

    The amplitude of the wave coming out of this circuit will
    then be proportional to the number of G's the mechanical circuit is
    subjected
    too.

    Very high frequencies are used as these capacitors are tiny to say the
    least.
    The basic capacitance is on the order of only one pico farad.

    The wave amplitude coming out can be rectified or converted to DC and
    then fed to an A to D for computer input. Use four of them
    mounted equally spaced in a circle and you have a angular rate sensor.

    This is an extremely simple idea and it is easy to make.
    One can make their own, in any shop, using nothing but hand tools,
    vastly scaled up from what one finds in a MEMS chip.

    Paul Lamar


    It seems that you are discounting the sensors based on vibrating beam
and
    the Coriolis effect.  Not sure why..  These are the sensors that
actually
    act like gyroscopes.


http://m.sensorsmag.com/sensors/acceleration-vibration/an-overview-mems-iner
tial-sensing-technology-970


    Regards,

    Matt-

    Again they are misusing the term "gyroscope" for marketing purposes
IMHO. A
    real gyroscope is a 3D device. A change
    in the Z axis of the real gyroscope results in a force in the X or Y
axis.
    You get both roll and
    pitch information from one device.

    "As a result, the gyroscope[???] provides accurate angular rate
sensing for
    rate changes from very small
    to very large, with minimal errors from short- or long-term drift."

    These are plainer devices hence they are angular rate sensors. It
takes two
    and computer
    integration to get roll and pitch information. The beam deflection
they are
    talking about
    here can be sensed by the same bridge capacitor electronics.

    http://en.wikipedia.org/wiki/Coriolis_effect

    "In physics, the Coriolis effect is a deflection of moving objects when
   they
    are viewed in a rotating reference frame. In a reference frame with
    clockwise rotation, the deflection is to the left of the motion of the
    object; in one with counter-clockwise rotation, the deflection is to
the
    right."

    Note: no mention is made of a 3D system.

    Also they are not telling you how they sense the deflection of the
sensing
    beam.


    Paul Lamar

    http://en.wikipedia.org/wiki/Vibrating_structure_gyroscope


    Matt-

    And: http://en.wikipedia.org/wiki/Halteres


    Matt-

   Agree that a vibrating structure gyro is not an accelerometer. It
   should measure absolute change in heading. It's closer to this:

   http://en.wikipedia.org/wiki/Foucault_pendulum

   -Chris

   No I don't agree.
   It is not a gyro!!!!!

   A pendulum senses the vertical. Is it a gyro. Hell no!!!!


   Paul Lamar

   Those links explain it pretty well. A vibrating structure that is
   vibrating in planes other than the vertical will display the same
   effect. This effect is completely independent of gravity, however the
   pendulum is simply a convenient way to illustrate it. Definitely not
   an accelerometer. Functions like a gyro, though I can see why the term
   is disputed.

   -Chris



  Hi, this seems useful:
http://electronicdesign.com/article/analog-and-mixed-signal/This-Year-s-Best
-Analog-Design-Will-Find-You-In-The-Dark.aspx?cid=ed_powernewsletter&NL=1&YM
_RID=
Murry I Rozansky

"In June, Analog Devices released the ADIS16407 iSensor inertial measurement
unit (IMU), which integrates a tri-axis gyroscope, tri-axis accelerometer,
tri-axis magnetometer, and pressure sensor, with associated signal
conditioning, in a single package (Fig. 1). That’s 10 degrees of freedom.
Every IMU is factory-calibrated for sensitivity, bias, alignment, and
temperature. Each sensor has its own dynamic compensation formulas,
maximizing accuracy of sensor measurements."

"The pressure sensor and the tri-axis magnetometer, which adds the ability to
sense the Earth’s magnetic field relative to the device, is the major
advance over the company’s ADIS16334, increasing the degrees of freedom from
six to 10."

"Navigation technology used in first responder or unmanned vehicles not only
requires multiple axes of sensing, precisely aligned, but also
cross-integrated to discern tracking/location in dynamic environments,” says
Bob Scannell, business development manager at Analog Devices. “Where no one
single sensor provides the required precision, the solution involves merging
multiple sensor types with a deep knowledge of the dynamics of the
application environment."