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Open-File Report 00-379

A Filter Circuit Board for the Earthworm Seismic Data Acquisition System

By Edward Gray Jensen

The Earthworm filter circuit boardAbstract

The Earthworm system is a seismic network data acquisition and processing system used by the Northern California Seismic Network as well as many other seismic networks. The input to the system is comprised of many realtime electronic waveforms fed to a multi-channel digitizer on a PC platform. The digitizer consists of one or more National Instruments Corp. AMUX–64T multiplexer boards attached to an A/D converter board located in the computer. Originally, passive filters were installed on the multiplexers to eliminate electronic noise picked up in cabling. It was later discovered that a small amount of crosstalk occurred between successive channels in the digitizing sequence. Though small, this crosstalk will cause what appear to be small earthquake arrivals at the wrong time on some channels. This can result in erroneous calculation of earthquake arrival times, particularly by automated algorithms. To deal with this problem, an Earthworm filter board was developed to provide the needed filtering while eliminating crosstalk. This report describes the tests performed to find a suitable solution, and the design of the circuit board. Also included are all the details needed to build and install this board in an Earthworm system or any other system using the AMUX–64T board. Available below is the report in PDF format as well as an archive file containing the circuit board manufacturing information.

First posted September 21, 2000

  • Archive file EXE (124 kB)
    Archive file containing the circuit board manufacturing information. NOTE: The file 'EWFilter.exe' is a PC, not a Mac, archive. People using Macs can download it and pass it on to a manufacturer for use in making the boards, but they cannot open the archive themselves.

For additional information, contact:
Earthquake Science Center, Menlo Park
U.S. Geological Survey
345 Middlefield Road MS 977
Menlo Park, California 94025

Part or all of this report is presented in Portable Document Format (PDF). For best results viewing and printing PDF documents, it is recommended that you download the documents to your computer and open them with Adobe Reader. PDF documents opened from your browser may not display or print as intended. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Jensen, Edward Gray, 2000, A Filter Circuit Board for the Earthworm Seismic Data Acquisition System: U.S. Geological Survey Open-File Report 00-379, 17 pp.,






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