Sensors

ver. 2011093

The PASSCAL Instrument Center (PIC) has historically honored requests to repair community owned broadband seismometers. Significant resources are required to process, evaluate, and repair a broadband instrument. To ensure that we are able to properly administer these requests and that we are offering these services consistently to all members of the IRIS community, the following policy will govern the PASSCAL Instrument Center's handling of these requests.

Instrument Response files released from Nanometrics for Trillium 120 and Trillium 240 sensors have been evaluated and updated for Antelope, where they are used to generate dataless and RESP files.

Introduction:

All equipment, especially sensors and cables, are cleaned and comprehensively tested when they arrive at the PIC, regardless of whether the equipment are newly delivered from the manufacturer or being returned from an experiment.  PASSCAL makes every effort to ensure that all equipment are operating to the manufacturers specifications.

This article outlines the procedures undertaken and metrics employed by the PIC to verify that sensors operate within manufacturers specifications.

Procedures:

All sensors returning from a field experiment are subject to the following procedures:

The CMG 40T-1sec seismometer looks, on the outside, just like the CMG 40T-30sec, intermediate period seismometer. Its response, however, is tuned to short-period signals (1-100Hz). One hundred of these feedback seismometers were purchased for the Flexible Array sensor pool.

All poles and zeroes in radians/sec

Cold Rated Guralp CMG-3T

The Guralp CMG-3T seismometer is a 3-axis broadband instrument that has a flat response to ground velocity between 120s and 100Hz.  It has been tested to operate down to -55C and only draws 0.3W of power.

PASSCAL's Polar program has purchased the cold-rated 3Ts (with active logic high) for broadband experiments in Antarctica.  When powered and locked, the reported mass positions will be '0'.  This does not mean that the instrument is dead or unpowered.  Once the 'unlock' command is initiated, first the lock/unlock and then the centering motors should run and finally result in meaningful mass position readouts.

The CMG-3T has a low tilt tolerance and is sensitive to temperature changes, it therefore requires a well established and well thermally isolated vault.

Your choice of seismic sensor for Polar research will depend on your scientific targets. PASSCAL has a wide range of both passive and active seismic sensors appropriate for controlled source, local or regional seismicity, ice dynamics or teleseismic studies. A comparison of our sensors can be found here.

Short Period Sensors

These are typically used for controlled source experiments, short term, local seismicity or ice studies.  The instruments available are the Sercel L-28 and L-22.  The L-28 is a 4.5Hz 3 component geophone while the L-22 is a 2Hz 3 component seismometer.

  Salient Features: This 3-channel sensor has a frequency of 4.5Hz, is critically damped at .707 and has a sensitivity of 32 V/m/s. Used for (but not limited to) active source (land and off-shore excitations), glacial movements, local earthquake and aftershock studies. Manufacturer Documents: http://www.geospacelp.com/      Click on the "Geophysical" button and then on the "GS-11" link. PASSCAL Documents: Connector wiring information here Installation & Troubleshooting Documents: Y-28 Orientation and Installation Tips here

Sensor Manufacturer Power Corner
Frequency Damping Sensitivity Poles and Zeroes STS-2 Streckeisen 30 ma @ 12vdc 0.0083 Hz 0.707 critical 1500 v/m/s *Depends on generation:

PASSCAL Intermediate-Period Sensors: Guralp CMG3-ESP Guralp CMG40T Nanometrics Trillium40 Features:

The low-period corner is 30 seconds for the 3 Guralps and is 40 seconds for the Nanometrics sensor. All are 3-component feedback sensors. The CMG40T and Trillium40 masses do not lock. One should still ship and handle them with care so as not to damage them. The CMG3-ESP has masses that require manual locking and unlocking.  For information on the CMG40T with corner-frequencies of 1-sec, click here.