Guralp Systems Limited
MAN-C3E-0005 - CMG-3ESPCD Digital Broadband Seismometer (CD24 Versions) - Technical Manual
Section Index: 4.1 Notes 4.2 Installing in vaults 4.3 Installing in pits 4.4 Rapid installations 4.5 Installing in post‑holes 4.6 Other installation methods 4.7 Networking overview 4.8 Setting up the Ethernet interface 4.9 Setting up wireless networking

Chapter 4. Installation

4.1 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 bedrock, 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. Alternatively, 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 acclimatise to the local temperature, and settle into their positions. This will take around four hours from the time installation is completed. If you require long-period recording, you should re-centre the instrument after this time.

4.2 Installing in vaults

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

4.3 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.

4.4 Rapid installations

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 4.3), since the data produced will be of significantly higher quality.

4.4.1 Deployment

4.4.2 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.

4.5 Installing in post-holes

The 3ESPCD is suitable for installation in potholes. In soft subsoil, a hole between two and four metres deep and 200 mm 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:

4.6 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.

4.7 Networking overview

The 3ESPCD can optionally be supplied with no networking, with a wired Ethernet connection or with both wired and wireless Ethernet connections.

Additional information about both modules is obtainable from Lantronix's web-site: www.lantronix.com.

The Lantronix modules are both twin-channel serial-to-TCP converters. Channel one's serial interface is exposed on the instrument's main connector; this can be used to provide networking capabilities to any external device with an RS232-compatible output. Channel two is internally connected to the standard digitiser output using an internal RS-232 link.

Note: If a serial device (such as Scream or a terminal emulator) is detected on the DATA port (via the break-out box), the networking module is automatically disconnected. Hence, networking is only available when the DATA port is disconnected.

Note: Note that the wired and wireless capabilities of the WiPort are also mutually exclusive: only one can be active at a time and, indeed, the wireless interface cannot even be configured when the device is in wired mode.

The illustration above shows serial data in blue, network data in yellow and power connections in red.

The Lantronix module can be powered down with the CD24 command

ETHER DISABLE

and powered up with the command

ETHER ENABLE

Certain operations, such as a firmware upgrade, can result in power to the Lantronix module being turned off. In these cases, the ETHER ENABLE command should be used to restore power.

4.8 Setting up the Ethernet interface

3ESPCD instruments with Ethernet features installed use an embedded Lantronix WiPort-NR module to provide the network interface. This module can be configured using a built-in Web server.

Before you can access the Web server, however, you will need to assign the device an IP address. This can be done using Lantronix' DeviceInstaller utility for Microsoft Windows, or using a DHCP server. You will need a PC with a network interface installed.

4.8.1 Using DeviceInstaller

4.8.2 Using DHCP

If you cannot install DeviceInstaller on your PC, or do not wish to, you can also get access to the 3ESPCD using a standard DHCP server. In most cases you will need to have administrative privileges to do this.

4.8.3 Configuration with the Web interface

Once you have access to the WiPort-NR's Web interface, you can configure it with its proper settings. Unless you have previously configured password protection, simply click if prompted for a user name and password.

4.9 Setting up wireless networking

3ESPCD instruments with wireless features installed use an embedded Lantronix WiPort module to provide the network interface. This module can be configured using the DeviceInstaller utility for Microsoft Windows, or using a DHCP server. You will need a PC with a wireless card installed.

You may find it easiest to gather together all the Wi-Fi hardware before taking it into the field, and configuring it from a local wireless-enabled PC.

3ESPCD instruments with the wireless networking option also have an ETHERNET port for attaching to a wired network. You can switch between the wired and wireless interfaces using DeviceInstaller.

Note: There are two types of wireless network topology supported by the WiPort, infrastructure and ad-hoc. GSL can only support 3ESPCDs running in infrastructure mode.

4.9.1 Using DeviceInstaller

4.9.2 Using DHCP

If you cannot install DeviceInstaller on your PC, or do not wish to, you can also get access to the 3ESPCD using a standard DHCP server. In most cases you will need to have administrative privileges to do this.

4.9.3 Configuration with the Web interface

Once you have access to the WiPort's Web interface, you can configure it with its proper settings. Unless you have previously configured password protection, simply click if prompted for a user name and password.

4.9.4 Installing wireless hardware

The small antenna supplied with the 3ESPCD is adequate for initial testing or temporary installations with an access point within 50 metres of the instrument.

To send data over a larger distance, or if the line of sight between the antenna and the access point is blocked, you will need to use a larger antenna.

You can reduce the power requirements by using a directional antenna pointed at the location of the access point. The access point does not need to be permanently present. For example, you could set up an array of 3ESPCD instruments with antennas pointed towards a prominent natural feature with a direct line of sight to all the instruments, and access them all from this location using a laptop PC.