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-inertial-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