Inertial Sensors : Servo-inclinometer & servo-accelerometer

A servo-inclinometer is an accelerometer type used in the earth’s gravity field (±1g).

This instrument consists of an inertial mass (pendulum) which:

  • Rotates around a torsion bar
  • Is servo controlled by means of an inductive torque, whose current is proportional to the applied acceleration

The position sensor is optical. For small angles, the measured acceleration can be considered as equal to the angle. It is necessary to make an Arc sine conversion to determine the angle of tilt for wider ranges.

This technology permits very sensitive inclinometers (< 0.5 arc seconds) without hysteresis, with 1.10-4 FSO accuracy and a high dynamic.

The sensing element is immersed in oil which provides a good resistance to the environment (shock, vibration). A torsion bar avoids friction problems.

The electronic servo loop is manufactured in hybrid technology.

All these elements give the transducer a very high reliability.

Meggitt (Sensorex) servo-inclinometers have passed all the tests defined in the most severe standards.

MEMS inertial sensors

Meggitt (Sensorex) also takes the best of new technology, provided by reliable partners ; in this respect, we have developed a range of inertial sensors based on a micro-machined silicium cell, also called MEMS (Micro Electro Mechanical Systems).

Our SX46000 cubic inclinometers & accelerometers series, the SX42891 display tilt sensor and our complete SX43030 & SX43040 inertial references all use this technology.

Accelerometer cell

The sensitive element of our inclinometers/ accelerometers consists of a seismic mass, held between 2 joints and assembled to 2 fixed electrodes.

Whenever an acceleration is applied, the seismic mass oscillates, and creates a differential capacity variation. An ASIC circuit detects this variation and converts it into an analogue signal, proportional to the applied acceleration.

A micro-chip takes care of the gain & the offset set-up, as well as the non-linearity correction.

Gyrometric cell

The sensitive element of the silicium gyrometers consist of a micro-machined ring, held by 8 equidistant arms. This ring is excited to its resonance frequency thanks to a servo-oscillator and the magnetic field generated by a magnet situated at the center of the ring.

Detectors placed all around the ring measure the voltage created in the ring. When the sensor is static, this voltage is null; but, when an angular speed is applied to the sensor, the voltage rises. This voltage is then cancelled by an opposed phase voltage, created by a servo-loop. This signal is thus proportional to the applied angular speed.