Carlos Campos, Robert Schofield.

We had a faulty Guralp 3T seismometer that would not unlock the pendula. When we contacted the supplier, we were told we could send it back to be diagnosed and fixed, or we could open it up on site. We choice to ladder, as we thought it was a simply mechanical issue.

fig 1  fig 2  fig 3 

The seismometer is protected by a metal outer layer as well as two layers of shielding, to reduce noise affecting the system. Additionally, the internal components are made of brass to further limit noise.

While looking around at the internal structures, we found that a ball bearing had fallen onto the table. We then searched for where it came from, as it was most likely the cause of the failure.

fig 4

The pendula that measure horizontal movement rest on a triangular base of two ball bearing and a drive screw. This drive screw is connected to a motor which can lock, unlock, and center the mass. This screw also sits on a ball bearing. This way, the pendula rock on the two free bearing, while the drive screw can control the movement of the masses.

fig 5

This is a picture of how the mass system should look like. The screw presses on the bearing and will push the mass up or pull it down.

fig 6

This is a picture of the problem pendulum. The ball bearing for the drive screw is missing. Meaning when the seismometer first tried to unlock and balance the mass, the motor drove the screw into the brass. This either caused damage to the screw, the bass, the motor, or all of the above.

The manufacture told us that we would have to ship it back so they could fix it.