Guralp Systems Limited
MAN-C3E-0002 - Güralp 3ESPCD Digital Broadband Seismometer (DM24 Versions) - Users' Guide

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1. Preliminary Notes 2. Introduction 3. Installing the 3ESPCD 4. Calibrating the 3ESPCD 5. Using Scream! 6. Command line interface 7. Inside the 3ESPCD 8. Appendix A - Connector pin-outs 9. Appendix B - Sensor Specifications 10. Appendix C - Digitiser specifications 11. Revision History

Section Index: 3.1. First encounters 3.2. Installation notes 3.3. Installing in vaults 3.4. Installing in pits 3.5. Other installation methods 3.6. Rapid installation 3.7. Installing in post-holes 3.8. Using the 3ESPCD

Chapter 3. Installing the 3ESPCD

3.1 First encounters

3.1.1 Unpacking

The 3ESPCD seismometer is delivered in a single transportation case. The packaging is specifically designed for the 3ESPCD and should be reused whenever you need to transport the sensor. Please note any damage to the packaging when you receive the equipment, and unpack on a safe, clean surface. The package should contain:

Assuming all the parts are present, stand the seismometer in the centre of a bench and identify its external features:

3.1.2 Serial number

The sensor's serial number can be found on the label stuck to the top lid of the sensor. You should quote this serial number if you need assistance from Güralp Systems.

3.1.3 Handling notes

The 3ESPCD is a sensitive instrument, and is easily damaged if mishandled. If you are at all unsure about the handling or installation of the device, you should contact Güralp Systems for assistance.

3.1.4 Connections

The instrument has the following connectors:

3.1.5 Power supply

The sensor requires a 12 V power supply, which it obtains through the DATA OUT port. You may wish to terminate the supplied power cable in order to connect a 12 V power source to this connector: it is supplied with bare ends. Using a 12 V, 25 Ah sealed heavy-duty lead-acid battery, you should expect the instrument to operate for around a week without recharging.

A power management module can be installed as an option, which allows the 3ESPCD to operate from a 10 – 15 V supply range. This module also cuts the input power to the sensor electronics if it drops below 10.5 V, to minimize discharge from battery-operated installations.

The 3ESPCD draws a nominal current of 200 mA from a 12 V supply when in use. During locking and unlocking of the sensor masses, this current rises briefly to 750 mA. It is recommended that you carry a spare 12 V battery when visiting an installation for maintenance, in case the sensor needs to be moved and the on-site batteries no longer have sufficient charge to perform the locking procedure.

3.1.6 FireWire

The digitiser has an IEEE.1394 (“FireWire”) port, which you can use to download data onto a compatible hard disk.

Before you can use the disk, you will need to erase/format it. The digitiser saves data on the hard disk in raw mode, so you cannot use a PC's standard software to reset the disk.

To erase/format a FireWire disk for use with the 3ESPCD:

You will now be able to download data onto the disk when required.

3.2 Installation notes

The goal of any seismic installation is to ensure that wave-trains arriving at the instrument accurately reflect the internal motion of subsurface rock formations. To achieve this, the seismometer and its emplacement need to be considered as a mechanical system, which will have its own vibrational modes and resonances. These frequencies should be raised as high as possible so that they do not interfere with true ground motion: ideally, beyond the range of the instrument.

In particular, the sensor needs to be protected against environmental factors such as

In seismic vaults, instruments are often installed on piers. It is important to ensure that the interface between the pier and the floor does not introduce noise, and that the pier itself does not have resonant frequencies within the passband. Ideally, a seismic pier will be significantly wider than it is high (to minimize flexing) and will form a single piece with the floor, e.g. by moulding a poured concrete floor with a wooden frame.

Many situations do not allow for the construction of a seismic vault. For example, you may need to deploy quickly to monitor the activity of a volcano showing signs of rejuvenation, or to study the aftershocks of a major earthquake; or the site itself may be too remote to ship in construction equipment.

Temporary installations can be protected against spurious vibrations by

After installation, the instrument case and mounting surface will slowly return to the local temperature, and settle in their positions. This will take around four hours from the time installation is completed. If you require long-period recording, you should re-zero the instrument after this time.

3.3 Installing in vaults

You can install a 3ESPCD in an existing seismic vault with the following procedure:

3.4 Installing in pits

For outdoor installations, high-quality results can be obtained by constructing a seismic pit.

Depending on the time and resources available, this type of installation can suit all kinds of deployment, from rapid temporary installations to medium-term telemetered stations.

Ideally, the sensor should rest directly on the bedrock for maximum coupling to surface movements. However, if bedrock cannot be reached, good results can be obtained by placing the sensor on a granite pier on a bed of dry sand.

3.5 Other installation methods

The recommended installation methods have been extensively tested in a wide range of situations. However, past practice in seismometer installation has varied widely.

Some installations introduce a layer of ceramic tiles between a rock or concrete plinth and the seismometer, as shown in the left-hand picture below:

However, noise tests show that this method of installation is significantly inferior to the same concrete plinth with the tiles removed (right). Horizontal sensors show shifting due to moisture trapped between the concrete and tiling, whilst the vertical sensors show “pings” as the tile settles.

Other installations have been attempted with the instrument encased in plaster of Paris, or some other hard-setting compound (left):

Again, this method produces inferior bonding to the instrument, and moisture becomes trapped between the hard surfaces. We recommend the use of fine dry sand (right) contained in a box if necessary, which can also insulate the instrument against convection currents and temperature changes. Sand has the further advantage of being very easy to install, requiring no preparation.

Finally, many pit installations have a large space around the seismometer, covered with a wooden roof. Large air-filled cavities are susceptible to currents which produce lower-frequency vibrations, and sharp edges and corners can give rise to turbulence. We recommend that a wooden box is placed around the sensor to protect it from these currents. The emplacement may then be backfilled with fresh turf to insulate it from vibrations at the surface, or simply roofed as before.

By following these guidelines, you will ensure that your seismic installation is ready to produce the highest quality data.

3.6 Rapid installation

This section details a method of deploying 3ESPCD instruments with the minimum of additional equipment. This is recommended for situations where seismic instrumentation needs to be installed very quickly, e.g. to study a resumption of volcanic activity, or where difficulty of access to the site prevents you from constructing a full seismic pit. You should always construct a pit if possible (see Section 3.4), since the data produced will be of significantly higher quality.

3.6.1 Deployment

3.6.2 Recovery

Care should be taken when recovering the 3ESPCD, since tapping or banging it can cause damage to the sensors inside. The following instructions assume that you have installed the instrument following the steps above.

3.7 Installing in post-holes

The 3ESPCD is suitable for installation in potholes. In soft subsoil, a hole 2 – 4 metres deep and 20 cm wide can be conveniently excavated using a tractor-mounted or hand-operated pothole auger. To minimize surface effects, you should ensure that the hole is at least 1 metre deeper than the length of the instrument, and preferably somewhat more.

Since the hole has no lining, it may occasionally flood. However, most soil types are sufficiently permeable to allow water to soak away, leaving the packing material moist.

To install a 3ESPCD in a pothole:

3.8 Using the 3ESPCD

Once the 3ESPCD is powered, it will start producing data immediately. You can now start configuring it for your own needs. There are three ways you can do this:

All three methods provide full access to the configuration options of the digitiser.

3.8.1 Retrieving data

You can configure the digitiser to operate in a number of transmission modes. These modes determine whether the unit stores data in its on-board Flash memory, sends it over the serial link in GCF format, or does some combination of these. See “Data flow ” in Section 5.2.5 for more details.

If you choose a transmission mode where some data are stored in Flash memory, you will need to recover this data at a later date. You can do this either over the serial link, or using the digitiser's FireWire interface.

To download data over FireWire, simply plug the disk in. If there are enough new data waiting to be transferred (by default 128 Mb), they will immediately be downloaded onto the disk. The internal pointers will be updated to mark the data as downloaded.

Alternatively, for more downloading options, issue the command DISKMENU from the digitiser's console before attaching the disk. See Section 6.7 for more information. You can use DISKMENU to download any section of data, whether or not it has already been transferred.

While the FireWire interface is active, it will consume about 200 mA of power (from a 12 V supply). If you interrupt a transfer whilst in progress, the digitiser will re-boot, but the data held in memory will not be affected.

To download data over the serial link:

3.8.2 Reading digitiser disks

The digitiser uses a special disk format, DFD, for recording data. You can read this data into a PC using Scream! or the GCFXtract utility, which is freely available from the Güralp Systems Web site.

Note: The DFD format is not the same as that used by the Güralp Systems EAM data modules, which use a FAT32-compatible or extn journalling file system.

Güralp Systems can provide fully-tested disks with FireWire and USB connectors. Alternatively, a third-party FireWire disk may be used (although compatibility is not guaranteed.)

3.8.2.1 Reading disks with GCFXtract

To read a disk using GCFXtract:

3.8.2.2 Reading disks with Scream!

You can also read disks with Scream!. This allows you to view data in the process of being transferred, but is slightly slower, because Scream! does not read data in strict order. To read a disk with Scream!:

More information is contained in the Scream! Manual, MAN-SWA-0001.

PreviousNext

1. Preliminary Notes 2. Introduction 3. Installing the 3ESPCD 4. Calibrating the 3ESPCD 5. Using Scream! 6. Command line interface 7. Inside the 3ESPCD 8. Appendix A - Connector pin-outs 9. Appendix B - Sensor Specifications 10. Appendix C - Digitiser specifications 11. Revision History