Guralp Systems Limited
MAN-ESP-0001 - 3ESP - Operator's Manual

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1. Preliminary Notes 2. Introduction 3. Installing the 3ESP 4. Calibrating the 3ESP 5. Accessories 6. Inside the 3ESP 7. Appendices

Section Index: 3.1. First encounters 3.2. Installation notes 3.3. Installing in vaults 3.4. Installing in pits 3.5. Installing in post-holes

Chapter 3. Installing the 3ESP

3.1 First encounters

3.1.1 Unpacking

The 3ESP seismometer is delivered in a single transportation case. The packaging is specifically designed for the 3ESP 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:

3.1.1.1 Serial number

The sensor's serial number can be found on the label stuck to the top lid of the sensor. It is also stamped onto the side of the sensor base, next to the N/S indicator, and into the lid itself. You should quote this serial number if you need assistance from Güralp Systems.

3.1.1.2 Handling notes

The 3ESP 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.

Caution: Do not bump or jolt any part of the sensor when handling or unpacking.

Caution: Do not kink or walk on the data cable (especially on rough surfaces such as gravel), nor allow it to bear the weight of the sensor.

Caution: Do not connect the instrument to power sources except where instructed.

Caution: Do not ground any of the signal lines from the sensor.

Caution: Do not move the instrument whilst the masses are unlocked. You should report any sign of loose components, or any sound of parts moving inside the instrument, to Güralp Systems.

3.1.2 Connections

The instrument has a 26-pin connector which can be joined using the cable provided to a digitizer or breakout box. Individually shielded twisted-pair cabling must be used for the sensor outputs, control lines and power supply. If you need to make up a suitable cable, you should confirm the cable type with Güralp Systems.

Connector pin-outs are given in Appendix A on page 38.

3.1.2.1 Using a digitizer

The 3ESP can be connected directly to any Güralp Systems digitizer using the signal cable provided. This is the simplest way to use a 3ESP instrument. All the instrument's functions are available through the digitizer, including centring, and in instruments equipped with the option, remote locking and unlocking.

We recommend that you keep the digitizer near the instrument if at all possible, to minimize the length of analogue cable required. Once digitized, the signal is robust to degradation by noise or attenuation. Keeping the digitizer in the quiet, stable conditions of a seismic installation also provides it with an optimum environment for the on-board ADCs.

3.1.2.2 The breakout box

This unit separates the lines in the signal cable, so you can connect a power supply, a recording system, and the hand-held control unit:

You can also use the breakout box to centre the sensor masses. If your 3ESP includes the remote locking and unlocking option, you will be supplied with a slightly different breakout box with additional buttons for locking and unlocking the masses.

The standard breakout box is rain resistant but not waterproof. If you intend to use a breakout box in your installation, you should site it away from potential flooding. If this is not possible, a larger unit is optionally available which can be immersed in water without damage. (The 3ESP itself is, however, completely waterproof.)

3.1.2.3 Power supply

The sensor requires a 12 V power supply, which it obtains through the socket and breakout box or digitizer. You will need to make up a suitable cable to connect a 12 V power source to the 10-pin connector on the breakout box (spare 10-pin mil-spec connectors are provided for this purpose.) 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.

If you prefer, you can power the 3ESP directly from the connector on the top panel (see Appendix A on page 38).

A power management module can be installed as an option, which allows the 3ESP 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 3ESP draws a nominal current of 75 mA from a 12 V supply when in use. During locking and unlocking of the sensor masses, this current rises briefly to 600 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.

3.1.2.4 Signal output

The sensors output voltages representing ground velocity on floating differential lines. The breakout box provides a RECORDER connector for attaching to a recording system or digitizer. You can use any multi-channel recording system, provided that it has high-impedance floating differential inputs.

If you are using a Güralp Systems digitizer, you can connect the instrument directly to the digitizer without using the breakout box; power will be supplied through the digitizer, which can also activate the sensor control lines.

The breakout box also provides a CONTROL output, which can be connected to the Hand-held Control Unit. This device lets you monitor output signals from the instrument, and perform on-site calibration. For more information, see Section 5.1, page 28.

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 3ESP 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.

pit-cutaway-bedrock

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.

3.4.1 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 (left):

pit-installation-with-tiles pit-installation-with-tiles-removed

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):

installation-in-plaster-of-paris installation-in-sand

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. Once in the box, the emplacement may 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.

installation-complete

3.5 Installing in post-holes

The 3ESP is suitable for installation in post-holes. In soft subsoil, a hole 2 – 4 m deep and 20 cm wide can be conveniently excavated using a tractor-mounted or hand-operated post-hole auger. To minimize surface effects, you should ensure that the hole is at least 1 m 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 3ESP in a post-hole:

PreviousNext

1. Preliminary Notes 2. Introduction 3. Installing the 3ESP 4. Calibrating the 3ESP 5. Accessories 6. Inside the 3ESP 7. Appendices