Guralp Systems CMG-5T Compact - Manual (Page 20)

CMG-5T Compact
4 Inside the 5T Compact
The 5T Compact unit is constructed of hard-anodised aluminium with
“O” rings throughout, ensuring a completely waterproof housing.
Inside, the masses of the vertical and horizontal components are
attached to the rigid frame with parallel leaf springs. The geometry of
the spring spacing, together with the symmetrical design, ensures large
cross-axis rejection. The sensor mass is centred between two capacitor
plates and moves in a true straight line, with no swinging motion.
Feedback coils are attached to either side of the sensor mass, forming a
constant-flux, force-feedback transducer.
The vertical and horizontal sensors are identical in mechanical
construction; the vertical sensor's mass spring system is adjusted to
compensate for gravity. They are mounted directly onto the base above
the feedback control board.
The signal and feedback circuits inside the 5T Compact accelerometer
are arranged according to the following diagram:
The mass and the capacitor plates are energised by a two-phase
transformer driver, forming a differential capacitor. This acts as a
capacitive transducer, whose signal is then demodulated with a phase-
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