Chapter 2. Introduction

Güralp Systems’ 3-series instruments employ delicate pivots to suspend the masses so, because of the risk of damage while the instrument is being moved, mass-locks are provided to clamp the masses rigidly against the frame. The pivots will almost certainly be damaged if the instrument experiences any significant force while the masses are unlocked.

If it is essential to move an instrument with the masses unlocked, gently tilt it through 45° about the North-East access and carry it at this angle. This will ensure that the masses are resting against the frame while the instrument is being moved, reducing the risk of damage to the pivots.

The mass-locking mechanisms for horizontal and vertical component sensors differ but both use a motor and gearbox to drive a cam, which acts on a sprung bar. One end of the bar attaches to the frame and the other end has a pin attached which protrudes through the cap plate (the metal plate parallel to and immediately adjacent to the mass). When the crown of the cam pushes against the spring, the pin forces the mass to one end of its travel, where it is immobilised by a number of ball-bearings which fit into precisely machined cavities.

For horizontal component sensors, the cam is attached directly to the gearbox output shaft. For the vertical sensor, an additional 1:1 gear-train is used.