Complete CMG-3T vault installation

This “how-to” will help you set up a Güralp CMG-3T instrument and CMG-DM24 digitizer in a seismic vault, with (optionally) a DCM to connect them to a local computer network.

Installing the units

The CMG-3T instrument

Unpacking

The 3T seismometer is delivered in a single transportation case, containing three separate packages. The packaging is specifically designed for the 3T 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:

the seismometer;
a cable to join the sensor to the breakout box;
the breakout box (which provides separate connections for the signal, control and power lines);
a Handheld Control Unit (HCU) for monitoring sensor outputs and calibration, if ordered;
a 10-pin connector for your power lead (see below); and
a calibration and installation sheet.

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

a handle with North indication,
a multi-pole socket for input and output,
a spirit level,
three adjustable feet, and
two accurate orientation pins (one brass and one steel).

Serial number

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

Handling notes

The 3T 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.

Do not bump or jolt any part of the sensor when handling or unpacking.
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.
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.
Do not connect the instrument to power sources except where instructed.
Do not ground any of the signal lines from the sensor.

Connections

The instrument itself has a single connector, which can be joined using the cable provided to the 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.

The breakout box

This unit allows you to connect a power supply, a recording system, and the handheld control unit:

3T-breakout-box-connected

You can use the handheld control unit to centre, lock and unlock the sensor masses.

To unlock the sensor masses, press the ENABLE and UNLOCK buttons simultaneously. The BUSY LED will light. All three masses are unlocked, each in turn. The sensor then automatically moves on to centre the masses, during which time the BUSY LED will flash. When the BUSY LED goes out, the instrument is ready for use.

You should not attempt to move the instrument without re-locking the masses.
To lock the sensor masses, press the ENABLE and LOCK buttons. When the BUSY LED goes out, the instrument is ready for transportation.
To re-centre the sensor masses, press the ENABLE and CENTRE buttons. When the BUSY LED stops flashing, the centring process has finished. You may need to initiate several rounds of centring before the instrument is ready; when no more centring is required, pressing the ENABLE and CENTRE buttons has no effect.

The ENABLE, LOCK, CENTRE and UNLOCK buttons require only a single quick press to initiate the processes. Do not hold them down.

Power supply

The sensor requires a 12 V power supply, which it obtains through the socket and breakout box. 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.

Installation notes

For the best possible results, a seismometer should be installed on a seismic pier in a specially-built vault, where conditions are near perfect. Here, wave-trains arriving at the instrument reflect very well the internal motion of subsurface rock formations. However, this is not always feasible. For example,

instruments may need to be deployed rapidly, perhaps to monitor the activity of a volcano showing signs of rejuvenation, or to study the aftershocks of a major earthquake;
installations may be required in remote locations, or otherwise in circumstances where it is unfeasible to build a vault.

In these situations, 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. This is done by

standing the sensor on bedrock where possible, or at least deep in well-compacted subsoil;
clearing the floor of the hole of all loose material; and
using as little extra mass as possible in preparing the chamber.

In temporary installations, environmental factors are also important. The sensor needs to be well protected against

fluctuations in temperature,

turbulent air flow around walls or trees, or around sharp corners or edges in the immediate vicinity of the sensor;
vibration caused by heavy machinery (even at a distance), or by overhead power lines.

This can be done by selecting a suitable site, and placing the instrument in a protective enclosure. An open-sided box of 5 cm expanded polystyrene slabs, placed over the instrument and taped down to exclude draughts, makes an excellent thermal shield.

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.

Vault installation

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

Unpack the sensors from their container, saving the shipping boxes for later transportation.
Prepare the mounting surface, which should be smooth and free of cracks. Remove any loose particles or dust, and any pieces of loose surfacing. This ensures good contact between the instrument's feet and the surface.
If it is not already present, inscribe an accurate North-South line on the mounting surface.
Place the sensor over the scribed line, so that the brass and steel pointers are aligned with the marked directions, with the brass pointer facing North. This can be done by rotating the base of the sensor whilst observing it from above. The brass pointer can be found next to one of the feet.

If you cannot easily see the pointers, you should align the sensor using the north arrow on the handle. However, the alignment of the handle with the sensors inside is less accurate than the metal pointers, so they should be used wherever possible.
The top panel of the 3T includes a spirit level.

Level the sensor by adjusting each of the three feet of the instrument in turn, until the bubble in the spirit level lies entirely within the inner circle. (The instrument can operate with up to 2 ° of tilt, but with reduced performance.)

To adjust the height of a foot, loosen the brass locking nut and screw the foot either in or out. When you are happy with the height, tighten the brass locking nut to secure the foot. Gently check the foot to ensure that it is locked.
Connect the sensor to the breakout box, or a Güralp digitizer if you are using one.

The remainder of these instructions assume you are using a breakout box. The Güralp DM24 digitizer allows you to access all the functions of the seismometer through the digitizer instead; you should refer to its documentation for more details.
Connect a 12 V power supply through the breakout box.
Unlock the sensor by pressing the ENABLE and UNLOCK buttons on the breakout box together. Wait for the BUSY LED to start flashing, and then go out. After this point, you should be careful not to allow the instrument to tilt by more than 10 °, otherwise damage may result to the instrument.
Check the mass position outputs using a digital multimeter, digitizer or the handheld control units. If required, re-centre the masses by pressing the ENABLE and CENTRE buttons on the breakout box together.
Cover the instrument with thermal insulation, for example, a 5 cm expanded polystyrene box. This will shield it from thermal fluctuations and convection currents in the vault. It also helps to stratify the air in the seismometer package. Position the thermal insulation carefully so that it does not touch the sensor package.
Ensure that the sensor cable is loose and that it exits the seismometer enclosure at the base of the instrument. This will prevent vibrations from being inadvertently transmitted along the cable.

The DM24 digitizer

DM24S6-case-connectors

Connect Güralp seismometers to the SENSOR A and SENSOR B ports as necessary, using the data cables provided with the instruments.
Connect a GPS unit to the GPS port. If you are using a third-party GPS, you will need to make up a serial cable ending in a 10-pin mil-spec socket.
If you are using a DCM, connect the DATA OUT port to the straight-through cable from the DCM.
Otherwise, connect a Güralp combined serial/power cable to the DATA OUT port. Make up a connector if necessary, and attach the power lines to a 12 V DC power supply. Connect the 9-pin serial socket to your computer.

The digitizer will start up automatically as soon as it is provided with power.

Setting up a DCM

DCM-case-side

Connect Güralp digitizers, digital instruments, SAMs, CRMs or DCMs to PORT A and PORT B as necessary, using the serial data cable provided.
If you are using the DCM's USB capabilities, connect your external hardware or computer to the USB socket.

Note: USB distinguishes between hosts and clients. The DCM can act as either, depending on the options you specified at manufacture. If your DCM is a host, you can attach external USB peripherals such as hard disks. If it is a client, you can attach it to a computer, and it will appear as a network interface.
Connect a Güralp combined serial/power cable to the DATA OUT port. Make up a connector if necessary, and attach the power lines to a 12 V DC power supply.

Connect the 9-pin serial socket to a computer for configuration.
If you want to connect the DCM to a local area (Ethernet) network, you will need to set it up first.

When you connect an Ethernet cable to the NETWORK socket, the DCM will ask to be assigned an IP address from a DHCP server on your network.

If you use DHCP on your network, and you want to access the DCM's Web server or console over the network, you will need to find out from the DHCP server which address it has given the DCM.

If you only want the DCM to act as a router or forwarder, and intend to administer it using its serial console, you do not need to know its IP address.

If you do not use DHCP on your network, or you want to fix the address the DCM uses, you will need to give it an IP address through its console interface first (see below.)
Open the DCM's console over the serial connection. You can do this with minicom (for Linux) or hypertrm (for Microsoft Windows).

Alternatively, open Scream! and select File → Terminal.... Choose the serial port you have attached to the DCM, set the baud rate to 115200, and click Connect.

You should see the message
```
dcm login:
```
Enter root and the administrator password. If you have not been given a password, the default setting is rootme. The DCM will reply with a prompt:
```
[root@dcm ~]#
```
You should change the password as soon as you can with the command passwd.
Set the network parameters of the DCM with
```
[root@dcm ~]# gcfgdbset net.eth.0.address dcm-address
[root@dcm ~]# gcfgdbset net.eth.0.netmask network-mask
[root@dcm ~]# gcfgdbset net.eth.0.gateway network-gateway
[root@dcm ~]# gcfgdbset net.eth.0 static
```
In these commands, dcm-address is the IP address you want the DCM to use (e.g. 192.168.0.10); network-mask is the IP network mask (e.g. 255.255.255.0); and network-gateway is the IP address of the gateway computer (e.g. 192.168.0.1). The final command tells the DCM not to request its IP address from a DHCP server.
If you have access to the local network, you should soon be able to connect to the DCM's Web server by typing into your browser
```
http://dcm-address/
```
You can now configure the DCM and attached digitizers over the Web interface.
If you prefer, continue using the gcfgdbset command to configure the DCM.

From the DCM, you can connect to the console of attached digitizers with the command
```
minicom -s port-name 
```
Alternatively, you can send individual commands to a digitizer with the command
```
gcli port-number command
```
In these commands, port-number is the port number and port-name the port device name to send the command to. To find out these, issue the command serialmap:
```
Library version: libserialmap Version 1.0.5 with LIBGCONFIGDB
3 serial ports
 Port  0, Key   7000, name Data out port, device /dev/ttySA0, baud 115200
 Port  1, Key   7001, name Port B, device /dev/ttySA1, baud 9600
 Port  2, Key   7002, name Port A, device /dev/ttySA2, baud 19200
```
Each port will be listed, with its number number (e.g. 0), name (e.g. Data out port), and device (e.g. /dev/ttySA0). The port device name for minicom is the last of these, omitting the /dev/:
```
minicom -s ttySA2
```
You can connect to the DCM's command line over the network at any time using SSH. The DCM is not visible in Scream!, because data streams pass through it transparently. You can control attached digitizers and instruments over the link, through any number of intervening DCMs.
The easiest way to retrieve data from the DCM is to remove the internal hard disk, and attach it to any computer supporting either Firewire or the USB Mass Storage Protocol. It will appear on the computer as an extra hard drive.
To retrieve data from the DCM over HTTP or HTTPS, log in to its Web interface and click Disk files, followed by the name of the file you want to download.

Configuring the station

Through a direct serial connection

You can configure the installation directly using Scream!, by connecting the serial port of a computer to the DATA port of the digitizer.

Start Scream!, and wait for the digitizer to be shown in the main window.
Right-click on the digitizer’s icon and click Configure....

The Configuration Setup window will be displayed:
Change the System Identifier to a unique value for this installation, and select the sensor type you are using.
Click on the Output Control tab to display a tap diagram.

Güralp digitizers have four output stages, called taps, which represent successive decimation filters being applied to the incoming data. The decimation filters divide the and each tap outputs data at a rate 2, 4, 5
Use the menu boxes on the left to choose the configuration →200 →100 →10 →1.
Next to the 100 samples/s tap, check the Z, N and E boxes in the top row. This makes the digitizer produce data constantly at 100 samples/s.
Next to the 1 sample/s tap, check the Z, N and E boxes in the top row.
If you need to change any of the other settings in the Configuration Setup window, do so now.
Click UPLOAD, and wait for Scream! to pass the new configuration to the digitizer and reboot it. This will take about 30 seconds.
When the digitizer is back online, return to the main window, right-click on the digitizer’s icon and click Control....
Click on the Data Flow tab to display the window shown above.
Select Direct for the Transmission Mode. (The Buffering setting may be ignored.)

In direct mode, the digitizer will send all the data it produces directly out through its DATA port to Scream!, using the Güralp Block Recovery Protocol.
Click Apply to send the instructions to the digitizer.

The installation is now active.

Over a network

If your instrument is connected to the local network through a DCM, you can configure it

using the DCM's Web page interface,
by setting up a network server on the DCM and connecting to it using Scream!, or
by sending commands to it from the DCM's console.

If the DCM is connected to your computer through a direct serial link, it will automatically forward any data it receives through PORT A or PORT B.

As soon as Scream! receives data, whether over the network or a direct serial connection, the digitizer will appear in the main window, and you can configure it as above.

Setting up the DCM's Scream! server

The DCM can act as a GCF server on your network, which Scream! can connect to. Once you have set this up, you can then configure the instrumentation from a copy of Scream! running anywhere on the network.

Use a Web browser to navigate to the address of the DCM on your network:
```
http://dcm-address/
```
where dcm-address is the IP address of the DCM, configured above.
In the menu tree on the left, under Data transfer → Scream, click on Server.
Set datatransfer.scream.server to on, and enter a suitable port number for datatransfer.scream.server.port. It is usual to choose a port number in the range 1024 – 65535.
Click Save changes.
Install Scream!, if necessary, and run it.
Right-click on the Network icon, and click Configure... from the pop-up menu to open the Network Control window.
In the My Client tab, right-click in the space beneath Servers in the upper panel and select Add UDP server... from the pop-up menu.
Enter the numeric IP address and port number of the DCM's Scream! server, e.g.
```
192.168.0.1:5127
```
Click OK. The server should appear in the list under Servers.
Right-click on the DCM's entry in the list, and choose GCFSEND:B to instruct the DCM to begin sending data.
The DCM, and any attached instruments, should now appear in Scream's main window. You can now configure these instruments inside Scream! (see above) or view data as required.

Configurating the digitizer over the Web

If you prefer, you can change the configuration of the digitizer from the DCM's on-board Web server without using Scream!.

In the menu tree on the left, under Actions → Digitizer Setup, the DCM lists all the serial ports which are available for connecting to digitizers. On a stand-alone DCM, these will be Serial Port A, Serial Port B and Data Out Port.. Click on the entry corresponding to the digitizer you have connected.
Change the System ID to a unique value for this installation, and select the sensor type you are using.
Below the System ID is a table displaying the output configuration of the sensor.
Use the menu boxes on the left to choose the configuration →200 →100 →10 →1.
Next to the 100 samples/s tap, check the Z, N and E boxes in the top row. This makes the digitizer produce data constantly at 100 samples/s.
Next to the 1 sample/s tap, check the Z, N and E boxes in the top row.
If you need to change any of the other settings in this window, do so now.
Click Save changes, and wait for the DCM to pass the new configuration to the digitizer and reboot it. This will take about 30 seconds.

The installation is now active.