Noise Type
Possible Cause
The mass positions are large,
but slowly trending towards zero,
and one or more of the main
velocity outputs has an offset on
the order of several volts.
The Trillium Compact is powered and not level or was powered
during leveling.
When a Trillium Compact is left powered while not level, it can
take as long as a few hours for the unit to recover after leveling.
More importantly, when in this state, the unit is unresponsive to
ground motion. For short-term deployments or when
immediate confirmation that the sensor is working properly is
required, briefly setting the seismometer in short-period mode
allows the unit to recover immediately and produce ground-
motion recordings.
For fast recovery after leveling do one of the following
l
Leave the sensor unpowered until after it is level
l
Power cycle the unit, which momentarily puts the unit in
short-period mode during start up
l
Access the user interface, put the unit into short-period
mode, and then immediately return it to long-period mode
(see
l
Use the control lines on the digitizer to briefly put the unit
into short-period mode, and then return it to long-period
mode
Table 4-1 -
Types of noise and possible causes for posthole deployments (Continued)
Noise Type
Possible Cause
Spikes on horizontal channels
l
The feet of the seismometer are not locked.
l
There is a force pulling on the cable.
l
There is something touching the sides of the seismometer.
Continuous low frequency
wander (random noise, larger on
horizontal channels)
l
Insulation is missing or not well sealed, allowing drafts to
blow over the seismometer.
l
There are forces, such as wind, acting on the installation.
Spikes on the vertical channel
l
Usually due to electrical system noise. For example, power
supply noise from a battery charging circuit, or interference
from a strong magnetic or radio source that is nearby.
Table 4-2 -
Types of noise and possible causes for vault deployments
Chapter 4 - Post-Installation Activities
16889R10 • 2020-11-12
Page 50
