Although it has a rugged design, the 6TD is still 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 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.
Move the instrument with care, and report any sign of loose components or 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.
All parts of the 6TD are waterproof.
The instrument
The 6TD's output connectors are all located on the sensor lid. The sensor can be supplied with a number of options, so not all the connectors may be present on your instrument.
All 6TD instruments have a 19-pin mil-spec connector which carries power, data and GPS signals. The supplied breakout box (see below) provides individual connectors for these, or you can make up your own cable if you prefer.
The 6TD may also have connectors for the FireWire, Ethernet or Wi-Fi interfaces.
The connectors for the FireWire and Ethernet options are both six-pin mail-spec plugs. If the labelling has become illegible for any reason, they can be distinguished by noting that the FireWire connector lies to the East of the instrument and the Ethernet connector to the North-East, as in the picture below (which shows an early, unlabelled unit).
In addition to the cable to the instrument, which is moulded into the case, the breakout box provides
a 6-pin mil-spec socket for connecting the supplied GPS unit;
a 10-pin mil-spec plug for connecting to a PC's serial interface or a Güralp data module; and
a 6-pin mil-spec plug for connecting a 12 V power supply.
You may need to attach a suitable connector to the power cable provided. The 6TD draws a nominal current of 75 mA from a 12 V supply when in use; thus, 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.
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 infeasible 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.
You can install a 6TD 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 6TD includes a spirit level.
Level the sensor using each of the adjustable 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.)
The feet are mounted on screw threads. To adjust the height of a foot, turn the brass locking nut anticlockwise to loosen it, and rotate the foot so that it screws either in or out. When you are happy with the height, tighten the brass locking nut clockwise to secure the foot.
When locked, the nut should be at the bottom of its travel for optimal noise performance.
Connect a 12 V fused power supply to the breakout box.
Connect the data cable to a PC. Run Scream!, and check that data is being produced. Optionally, also check the mass position outputs (streams ending M8, M9 and MA.) These streams are digitized at a slower rate, and may take up to 15 minutes to appear.
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.
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.
Prepare a hole of 60 – 90 cm depth to compacted subsoil, or down to the bedrock if possible.
On granite or other hard bedrock, use an angle grinder to plane off the bedrock at the pit bottom so that it is flat and level. Stand the instrument directly on the bedrock, and go to step 7.
On soft bedrock or subsoil, you should install a pier as depicted below.
Pour a layer of loose, fine sand into the pit to cover the base. The type of sand used for children's sand-pits is ideal, since the grains are clean, dry and within a small size range. On top of the sand, place a smooth, flat granite plinth around 20 cm across, and shift it to compact the sand and provide a near-level surface.
Placing a granite plinth on a sand layer increases the contact between the ground and the plinth, and improves the performance of the instrument. There is also no need to mix concrete or to wait for it to set.
Alternatively, if time allows and granite is not available, prepare a concrete mix with sand and fine grit, and pour it into the hole. Agitate (“puddle”) it whilst still liquid, to allow it to flow out and form a level surface, then leave to set. Follow on from step 7.
Puddled concrete produces a fine-textured, level floor for emplacing the seismometer. However, once set hard, the concrete does not have the best possible coupling to the subsoil or bedrock, which has some leeway to shift or settle beneath it.
Alternatively, for the most rapid installation, place loose soil over the bottom of the pit, and compact it with a flat stone. Place the seismometer on top of this stone. This method emulates that in step 3, but can be performed on-site with no additional equipment.
Set up the instrument as described in Section 3.4, page 18 (steps 4 to 9).
The instrument must now be shielded from air currents and temperature fluctuations. This is best done by covering it with a thermal shield.
An open-sided box of 5 cm expanded polystyrene slabs is recommended. If using a seismic plinth on sand (from steps 3–4 or 5), ensure that the box is firmly placed in the sand, without touching the plinth at any point. In other installations, tape the box down to the surface to exclude draughts.
Alternatively, if a box is not available, cover the instrument with fine sand up to the top.
The sand insulates the instrument and protects it from thermal fluctuations, as well as minimizing unwanted vibration.
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.
Cover the pit with a wooden lid, and back-fill with fresh turf.
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):
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. 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.
The 6TD is specially designed for rapid installation, and may be fully installed in a few hours. This section details a method of deploying 6TD 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 3.5, page 20), since the data produced will be of significantly higher quality.
Prepare a hole of 60 – 90 cm depth to compacted subsoil, or down to the bedrock if possible.
Clean the hole down to the bottom, and remove any loose material from the mouth. Ensure that the bottom of the hole is relatively flat.
If the bottom of the hole is made of hard rock, you may need to put in some loose sand or soil so that the sensor can be levelled.
Connect the sensor to cables for the GPS unit and power source. If your 6TD has the Wi-Fi option, connect your antenna to the sensor.
Carefully insert the instrument into the hole, protected by a tough plastic bag to keep water out. Use a bag strong enough to bear the weight of the sensor and breakout box, so that it can be recovered easily.
Press the sensor down firmly into the soil, without tapping or hitting it.
Check the bubble level on top of the instrument package.
Adjust the instrument's position if necessary so that the bubble lies entirely within the black circle.
Pack soil or sand around the instrument to hold it steady. Make sure the soil or sand is firmly compacted and not at all loose.
Recheck the bubble level. If you cannot adjust the soil packing at this stage and the sensor is not level, you will need to clear the hole and restart from step 3.
Place the breakout box and any excess cable on top of the sensor, inside the plastic bag.
Group the cables coming from the bag for a distance of about 1 m, and keep them together with insulating tape.
Tie the top of the package and fold it over so that water cannot get in. Leave any excess cable within the bag.
Cover the installation with soil or sand until it is no longer visible.
Attach a GPS unit to the cable coming from the sensor. Position it so that it has a good view of the sky.
If possible, place the GPS near the instrument so that it can be found more easily.
If you are installing a 6TD with Wi-Fi, connect and install the antenna.
Bury the cables so that they cannot be seen.
If you are using a battery as a power source, dig a second hole for it. This hole does not need to be as deep as the pit for the instrument—perhaps 10 cm plus the height of the battery.
Attach the sensor power cable to the battery, and wrap it in another plastic bag. Place the bag in the hole.
Tie the bag and fold over, to make the battery as waterproof as possible.
Bury the power cable between the battery and the instrument, and compact soil or sand around the bag.
Fill in and cover the hole so that it is not visible.
Care should be taken when recovering the 6TD, 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.
Find the GPS receiver, which will be the only feature visible from the surface, and follow the buried data cable from it to the instrument.
Carefully remove earth from the hole until you find the power cable coming from the instrument.
Follow the power cable to the battery pit, and carefully dig away the soil to reveal the battery about 10 cm from the surface.
Disconnect the power cable from the battery. (With the power off, the sensor is less likely to suffer electrical damage during recovery.)
Return to the location of the sensor, and dig down to it. You should be able to remove a spade's head depth of soil without hitting the instrument. Beyond that, using a small hand shovel, follow the wires and carefully remove the remaining soil until you can see the plastic bag. Take special care not to damage the wires, which should be tied together in the vicinity of the bag.
Carry on removing soil, either with your hands or (very carefully!) with the shovel, until the whole bag is uncovered to about half the height of the instrument.
If the hole is relatively dry, open the bag and remove the breakout box and cabling. Lift the instrument out by its handle.
Do not lift the instrument by any of the attached cables. Straining the cables may result in invisible damage, making future installations unreliable.
Alternatively, if the hole is waterlogged, carefully lift out the entire bag in one piece, and remove the contents at the surface.
CMG-6TD instruments with Ethernet features installed use an embedded Lantronix X-Port 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.
Using DeviceInstaller
Download and install the DeviceInstaller utility from the Lantronix Web site at http://www.lantronix.com/
DeviceInstaller also requires the Microsoft .NET framework to be installed. If you do not have this already, it can be downloaded at http://www.microsoft.com/
Find out the MAC address of the 6TD's network interface. This should be printed on a label on the case.
If the Data Out port on the breakout box is connected to anything, disconnect it.
Connect the 6TD's ETHERNET port to the the PC's network interface, either using a crossover Ethernet cable or through a network hub.
Using a hub, you can connect several 6TDs to the same PC and configure them all at the same time.
DeviceInstaller will not work through routers or across the Internet. All the devices need to be on the same network segment as the PC.
Run DeviceInstaller.
DeviceInstaller's main window has two panels, a tree on the left (with Lantronix Devices at the top) and a table on the right.
The program will automatically look for Lantronix devices on all of your computer's network interfaces. If necessary, you can narrow the selection by clicking on an entry in the tree on the left.
An X-Port entry should appear in the table on the right, denoting that a device has been detected.
If more than one X-Port entry appears, DeviceInstaller has detected several devices.
For every detected device, the program shows the Hardware Address (i.e. the MAC address), and the IP address it is currently using. If your local network uses a DHCP server, the device will ask the DHCP server to assign it an address. Otherwise, a random address will be chosen automatically.
Automatic random addresses all begin with 169.254. The 6TD will choose a different one every time it is power cycled or rebooted.
The address of the 6TD may be shown in red with the status Unreachable.
If this happens, the sensor and PC cannot communicate because they are not on the same subnet. Click Assign IP to start the IP configuration wizard.
Follow the instructions in the wizard to set the IP address, or configure DHCP if you are using a DHCP server. When you have finished, click Search to find the sensor with its new IP address.
If you want to configure the 6TD to use a static IP address, use the Assign IP wizard as above, and click Search again.
Double-click on the entry which corresponds to the 6TD you want to configure.
The right-hand panel will change to show the current properties of the device.
Switch to the Web Configuration tab, and click Go to open the Web configuration interface.
Alternatively, click Use External Browser to use your own Web browser to configure the instrument.
Follow the steps below to configure the module from its Web interface.
Using DHCP
If you cannot install DeviceInstaller on your PC, or do not wish to, you can also get access to the 6TD using a standard DHCP server. In most cases you will need to have administrative privileges to do this.
Install and start the DHCP service on your PC.
Connect the 6TD's ETHERNET port to the the PC's network interface, either using a crossover Ethernet cable or through a network hub.
Using a hub, you can connect several 6TDs to the same PC and configure them all at the same time.
DHCP will not work through routers or across the Internet. All the devices need to be on the same network segment as the PC.
Monitor the DHCP server to find out what IP address it gives to each instrument.
To configure a device, enter its IP address into a web browser.
Configuration with the Web interface
Once you have access to the X-Port's Web interface, you can configure it with its proper settings.
The Web page is divided into three. A menu on the left switches between pages of configuration options on the right. There is also a banner at the top, which tells you the current firmware revision and the MAC address.
To navigate around the Web site, click on the entries in the left-hand menu. When you have made changes to the settings on any page, save them by clicking OK before you leave the page.
The X-Port has two serial channels which you can connect to. By default these are exposed on ports 10001 and 10002.
Channel 1 (normally port 10001) is connected to a serial console which is exposed on the power port of the breakout box. If you have problems connecting to the 6TD, you can attach a standard Güralp Systems power/data cable to this port and use Scream! to access the console.
Channel 2 (port 10002) is connected to the 6TD's digital output, unless you have connected a serial data cable from the breakout box to a computer. If the breakout box is connected, the 6TD will send data streams through that interface rather than to the X-Port.
Click on Channel 2 – Serial Settings.
Set the Baud Rate to 19200. This is the default baud rate for the 6TD's digital output. If you change the baud rate in Scream! or using the terminal, you must come back to this page and change the Baud Rate setting.
The remaining settings can be left at their default values. Click OK to save your changes.
For full information on the X-Port's configuration options, please refer to the X-Port documentation, which is available on the Lantronix Web site, http://www.lantronix.com/
When you have finished setting up the X-Port, apply the new settings by clicking Apply Settings. The X-Port will re-boot with the new settings in effect.
If the Wi-Port is using an automatically chosen random IP (beginning with 169.254), the IP address will change when you do this. You will need to go back to DeviceInstaller to find out the new IP address.
CMG-6TD instruments with wireless features installed use an embedded Lantronix Wi-Port 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.
CMG-6TD 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.
There are two types of wireless network topology supported by the Wi-Port.
Infrastructure networks need additional hardware, such as wireless access points and routers, to work. Any host on the wireless network will communicate with the access point or router, which manages all the connections and ensures data is transmitted correctly. This device may also provide connectivity to the Internet or your local network.
Ad hoc networks can be set up with no additional hardware. Each host on the wireless network attempts to communicate directly with the other hosts.
Ad hoc networks are easy to set up, but they are only suitable with a small number of hosts. In seismic networks, infrastructure mode is normally preferred, since sensors do not need to communicate with each other.
Using DeviceInstaller in an infrastructure network
Download and install the DeviceInstaller utility from the Lantronix Web site at http://www.lantronix.com/
DeviceInstaller also requires the Microsoft .NET framework to be installed. If you do not have this already, it can be downloaded at http://www.microsoft.com/
Find out the MAC address of the 6TD's network interface. This should be printed on a label on the case.
Configure your wireless router or access point to use a network name (SSID) of LTRX_IBSS
Disable any security features of the wireless router or access point.
Run DeviceInstaller.
The main window has two panels, a tree on the left (with Lantronix Devices at the top) and a table on the right.
The program will automatically look for Lantronix devices on all of your computer's network interfaces. If necessary, you can narrow the selection by clicking on an entry in the tree on the left.
A Wi-Port entry should appear in the table on the right, denoting that a device has been detected.
If more than one Wi-Port entry appears, DeviceInstaller has detected several devices.
For every detected device, the program shows the Hardware Address (i.e. the MAC address), and the IP address it is currently using. If you are using a wireless router with a DHCP server, or an access point connected to a network with a DHCP server, the device will use DHCP to assign it an address. Otherwise, a random address will be chosen automatically.
Automatic random addresses all begin with 169.254. The 6TD will choose a different one every time it is power cycled or rebooted.
The address of the 6TD may be shown in red with the status Unreachable.
If this happens, the sensor and PC cannot communicate because they are not on the same subnet. Click Assign IP to start the IP configuration wizard.
Follow the instructions in the wizard to set the IP address, or configure DHCP if you are using a DHCP server. When you have finished, click Search to find the sensor with its new IP address.
If you want to configure the 6TD to use a static IP address, use the Assign IP wizard as above, and click Search again.
Double-click on the entry which corresponds to the 6TD you want to configure.
The right-hand panel will change to show the current properties of the device.
Switch to the Web Configuration tab, and click Go to open the Web configuration interface.
Alternatively, click Use External Browser to use your own Web browser to configure the instrument.
Follow the steps below to configure the module from its Web interface.
Using DHCP in infrastructure mode
If you cannot install DeviceInstaller on your PC, or do not wish to, you can also get access to the 6TD using a standard DHCP server. In most cases you will need to have administrative privileges to do this.
Install and start the DHCP service on your PC.
Configure your wireless router or access point to use a network name (SSID) of LTRX_IBSS
Disable any security features of the wireless router or access point.
Monitor the DHCP server to find out what IP address it gives to each Wi-Port in range. If necessary, power cycle the sensor(s).
To configure a device, enter its IP address into a web browser.
Using “ad hoc” mode
If you do not have a wireless router or access point, you can configure your computer to set up an ad hoc wireless network when the 6TD comes within range.
To configure Windows XP to set up an ad hoc wireless network:
Open the Control Panel and select Network Connections.
Right-click on the Wireless Connection icon and select Properties. Switch to the Wireless Networks tab.
Under Preferred networks, click Advanced. Select Computer-to-computer (ad hoc) networks only.
Ensure the Automatically connect to non-preferred networks box is not ticked. Click Close to return to the Wireless Network Connection Properties window.
Under Preferred networks, click Add.... Switch to the Association tab.
Fill in the Network name (SSID) of LTRX_IBSS
Set Network Authentication to Open and Data encryption to Disabled. Click OK.
The network connection should now be visible under Preferred networks, and in the main Wireless Network Connection window.
Initially, the network will be shown as Not connected.
Power cycle the 6TD. After a short while, your computer should report that it has connected to the LTRX_IBSS network.
Use DeviceInstaller to find the 6TD on the new network.
If your computer is configured to obtain its network address automatically, both it and the 6TD will be using automatic random IP addresses.
Automatic random addresses all begin with 169.254. Both hosts will choose a different one every time they are power cycled or rebooted, or when the wireless network connection is lost.
To prevent this happening, configure your computer to use a static IP address, and use the Assign IP wizard in DeviceInstaller to assign a static IP address to the 6TD.
Configuration with the Web interface
Once you have access to the Wi-Port's Web interface, you can configure it with its proper settings.
The Web page is divided into three. A menu on the left switches between pages of configuration options on the right. There is also a banner at the top, which tells you the current firmware revision and the MAC address.
To navigate around the Web site, click on the entries in the left-hand menu. When you have made changes to the settings on any page, save them by clicking OK before you leave the page.
Click on WLAN (Wireless Local Area Network) to open the WLAN Settings page.
Change the Network Name (i.e. SSID) from LTRX_IBSS to a suitable name for your installation. This name will be announced to any nearby wireless devices when they search for networks.
If you are using an ad-hoc network change the second Network Name box as well. Otherwise, deselect Ad Hoc Network Creation.
Under Wireless Network Security, set Security to WEP and configure the security parameters. If you do not do this, anyone will be able to access the 6TD and change its configuration.
Make a note of the security parameters you have used.
Click OK, followed by Apply Settings in the main menu. The Wi-Port will restart.
If the Wi-Port is still using an automatically chosen random IP (beginning with 169.254), the IP address will change when you do this. You will need to go back to DeviceInstaller to find out the new IP address.
If you are setting up an infrastructure network, configure your wireless access point or router to use the new name and security settings, and power cycle the 6TD to make it reconnect to the network.
Reconnect your computer to the wireless network using the new name and security settings.
The Wi-Port has two serial channels which you can connect to. By default these are exposed on ports 10001 and 10002. Channel 1 (normally port 10001) is connected to a serial console which is exposed on the power port of the breakout box. If you have problems connecting to the 6TD, you can attach a standard Güralp Systems power/data cable to this port and use Scream! to access the console.
Channel 2 (port 10002) is connected to the 6TD's digital output, unless you have connected a serial data cable from the breakout box to a computer. If the breakout box is connected, the 6TD will send data streams through that interface rather than to the Wi-Port.
Click on Channel 2 – Serial Settings.
Set the Baud Rate to 19200. This is the default baud rate for the 6TD's digital output. If you change the baud rate in Scream! or using the terminal, you must come back to this page and change the Baud Rate setting.
The remaining settings can be left at their default values. Click OK to save your changes.
For full information on the Wi-Port's configuration options, please refer to the Wi-Port documentation, which is available on the Lantronix Web site, http://www.lantronix.com/
When you have finished setting up the Wi-Port, apply the new settings by clicking Apply Settings. The Wi-Port will re-boot with the new settings in effect.
Installing wireless hardware
The small antenna supplied with the 6TD is adequate for initial testing or temporary installations with an access point within 50 m of the instrument.
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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 and more powerful antenna.
In infrastructure mode, 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 6TD instruments with antennas pointed towards a prominent natural feature with line of sight to all the instruments, and access them all from this location using a laptop PC.
Autonomous 6TD installations will need to be configured before deployment. You can do this either
using the graphical interface provided by Scream! (see chapter 4, page 49), or
over a terminal connection (see chapter 6, page 80).
Both methods provide full access to the configuration options of the built-in digitizer.
In particular, 6TD can operate in a number of filing 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 section 4.2, page 64, for more details.
The easiest way to download data over Firewire is to connect a suitable disk to the FireWire port of the 6TD and power cycle the instrument.
If you have ordered a 6TD with the powered FireWire option, you can attach the disk directly to the 6TD with no additional connections. Otherwise, you will need to connect the disk to a power source through the supplied adapter.
When the sensor restarts, it will automatically the disk and flush all new data to it.
If you do not want to restart the instrument, you can also flush data to disk manually:
Open the digitizer's console. To do this using Güralp Systems' Scream! software, right-click on the digitizer's icon (once it appears) and select Terminal.... From a Güralp DCM, issue the command minicom -n port-number.
Connect a suitable disk to the FireWire port of the 6TD. Power the disk if necessary.
Issue the command FLUSH
This will download all data from the 6TD that it has not already transferred. If you want to transfer the entire contents of Flash memory, use the command FLUSHALL. For more details, see page 103.
Close the terminal session. If you are using Scream! or a DCM, the 6TD should start transmitting immediately. Otherwise, you may need to issue the command GO to start transferring data.
The 6TD uses a special disk format, DFD, for recording data. This format is also used by other Güralp digitizers such as the DM24.
You can read this data into a PC using Scream! or the gcfxtract utility, which are freely available from the Güralp Systems Web site.
Note: The DFD format is not the same as that used by the Güralp Systems DCM data module, which uses a FAT32-compatible 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).
To read a disk using gcfxtract:
Attach the disk to your computer. You can use FireWire, USB, or any other interface supported by your computer and the disk.
Run gcfxtract and select the required disk from the drop-down list, then click Scan.
gcfxtract will scan the disk and display all the streams it finds in the selection area below. For each stream, the Stream ID and the number of blocks found are shown.
This operation requires roughly 12 Mb of available memory for every Gb of space on the disk. If you have a very large disk, your computer may have to use its hard disk to make enough space. This will slow down scanning considerably.
By default, all streams containing more than 100 blocks are selected for extraction. You can change which streams to extract by checking or unchecking the check box beside each stream.
You can check or uncheck all of the boxes using the Select all and Unselect all buttons. Clicking Invert checks all unchecked boxes, and unchecks all checked boxes.
Enter a path name into the Target Directory field, or use the Browse... button to find a directory. This will be used as the root directory for extracted data. If it does not exist, gcfxtract will create it.
Enter a format string into the Filename Format field. The syntax is the same as the format string in Scream! and full documentation is available by pressing the '?' button beside the format entry field in interactive mode.
Normally, gcfxtract outputs GCF files, to ensure all the information in the original data is retained. If you want to convert to a different format, select it from the Output Data Format drop-down box. gcfxtract can output in most of the formats supported by Scream!.
Data is automatically placed in time order and saved in multiple files, each file containing a contiguous segment of data. By default, data streams are recorded in files 60 minutes long. To change this to some other number of minutes, alter the value in the Data File Duration (mins) box.
For data streams, if there is a gap in the data, gcfxtract will start a new file anyway.
Status streams are also saved in in multiple files, but have a default length of 24 hours. To change this, alter the value under Status File Duration (hours).
When you are happy with the settings, click Extract to begin extracting the data.
Clicking Reset sets a flag on the disk which marks it as empty. Next time a digitizer wants to transfer data, it will begin at the beginning of the disk, overwriting the old data. When this happens, none of the old data can be extracted with gcfxtract or Scream!. Until then, however, you will still be able to retrieve all the data.
When you are finished, you should exit gcfxtract and then use your operating system's standard facility for un-mounting hardware (e.g. “Safely Remove Hardware” under Windows) before disconnecting the drive.
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!:
Attach the disk to your computer. You can use FireWire, USB, or any other interface supported by your computer and the disk.
Run Scream!, and select File → Setup... from the main menu. Select the Files tab.
Set the Base Directory, Filename Format and Data Format as described above. Also, if required, set the Post-processor and Granularity options to your preference. Consult the Scream! documentation for details.
Select the Recording tab, and check Auto Record—Enable for Data Streams and Auto Record—Enable for Status Streams. Click OK.
Scream! will remember the recording options you set in steps 3 and 4 for later occasions.
Select File → Read SCSI disk... from the main menu. Scream! will search for attached disks, and open a window with a list of all the streams it has found.
Select the streams you want to replay, and click Open. The disk will appear in the left-hand pane of Scream!'s main window, and the streams you have selected will start playing into the stream buffer, as well as being recorded.
When you have finished transferring the data, if you want to reset the disk, select File → Reset SCSI disk... from Scream!'s main menu. Select the disk you want to reset, and click OK.
There are several ways a 6TD instrument can connect to Scream!:
A direct serial connection can be made from the breakout box to your computer. This is the method we recommend for testing the instrument (see Section 2.2, page 9).
The serial port can also be used to connect an external modem. Details of how to connect modems are available on the Güralp Systems Web site.
Data can be received from the instrument over the optional Ethernet or wireless links. Before you can do this, you will need to set up its IP address and network configuration, as described in Sections 3.7 (page 28)and 3.8 (page 33.)
To connect to a 6TD over the network:
Run Scream!, and select Windows – Network Control from the main menu. Click on the My Client tab.
Right-click in the white panel beneath Server, and select Add TCP Server....
Input the IP address of the 6TD with the output port that you chose when configuring the network interface. If you accepted the defaults, this will be port 10002.
192.168.33.2:10002
Click OK.
After a short wait, an entry for the instrument should appear in the pane. Right-click on the entry and select Connect.
If the connection is successful, you should see blocks appearing in the Block Rx pane, and streams will appear in Scream!'s main window. Close the Network Control window.
