Читать книгу Global Navigation Satellite Systems, Inertial Navigation, and Integration - Mohinder S. Grewal - Страница 89

Force‐rebalance. A common design for electromagnetic accelerometers uses permanent magnets as part of the proof mass, surrounded by a voice coil used to keep the magnet in a fixed position. The current required in the coil to keep it there will then be proportional to the force applied.

Inductive designs. A drag cup is a non‐magnetic conducting cylindrical sleeve with a rotating bar magnet inside, so that the axial torque on the drag cup will be proportional to the rotation rate of the magnet. Analog automobile tachometers and speedometers use them with a torsion spring on the drag cup to indicate rpms or speed. They have also been used with mass‐unbalanced drag cups such that the magnet rotation rate required to keep the drag cup stationary in an accelerating environment is proportional to acceleration and each revolution of the magnet represents an increment in velocity – making it an integrating accelerometer. Two of these can also be concatenated together in series such that they also integrate velocity to get position. Although they have performed well as tachometers and speedometers, they have not yet been sufficiently accurate for inertial navigation.

Figure 3.5 Common input–output error types.