Guralp Systems Limited
MAN-EAM-0003 - Acquisition Modules and Platinum Firmware - Technical Manual

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1. Preliminary Notes 2. Equipment Overview 3. Initial set-up 4. Platinum Overview 5. Platinum Firmware Upgrades 6. Data Handling 7. Networking Configuration 8. Digitiser Configuration 9. Digitiser Synchronisation 10. Receiving Data 11. Recording and Retrieving Data 12. Transmitting Data 13. Building Networks 14. Monitoring Operations 15. Technical operation 16. Appendices 17. Revision history

Section Index: 15.1. Cylindrical Digitisers 15.2. DCM 15.3. 24 Channel DAS 15.4. Instruments with integrated CMG-EAMs

Chapter 15. Technical operation

15.1 Cylindrical Digitisers

Güralp Systems Ltd's cylindrical digitisers provide a CMG-DM24 and a CMG-EAM in a single package: a stainless steel or aluminium cylinder with an optional carrying/mounting bracket. An internal Spyrus PC card provides authentication and digital signing of CD1.1 frames and subframes.

The system is fitted with variable gain analogue inputs, tamper-detection lines on all key connectors and an internal USB storage device, which is available to external USB host devices such as laptop computers.

The connectors are significantly different from other packages. The analogue connectors are grouped at one end of the cylinder and correspond to similarly labelled connectors on a standard CMG-DM24:

The illustration shows a four-channel unit; the seven-channel unit has an additional connector for sensor B:

The digital connectors are arranged at the other end of the cylinder:

For more information on the ports see section 2.5. The connector pin-outs are given in section 14.1.1 and listed in the table below:

Port

Section

Sensor

Section 16.5.12

Auxiliary

Section 16.5.13

Power

Section 16.5.9

Data

Section 16.5.11

Net

Section 16.5.4

GPIO

Section 16.5.6

USB

Section 16.5.8

GPS

Section 16.5.10

15.1.1 Internal Connections

Internally, the digitiser module and acquisition module are connected using three serial lines. The exact connections depend on the synchronisation mode, determined by the service running on Port C of the acquisition module.

In all cases, the GCF data output from the digitiser module is connected to Port A of the acquisition module, which should be set to “GCF in” at 38,400 Baud. It is currently possible to set the Baud rate of the digitiser's data output port and of the EAM's Port A independently, leading to a loss of data communication between the two modules if the two do not match. If you wish to have a higher transfer rate between the two modules, both ends must have their Baud rates increased separately.

The digitiser module also exposes a dedicated console connection, which is internally attached to Port B of the acquisition module. This can be accessed from the command line of the acquisition module or, if desired, made accessible over the network. If you wish to disallow network access, set the service on the EAM's Port B to “none”. To enable access over the network, set the service on the EAM's Port B to “TCP serial converter. Serial data to TCP link converter” and configure the converter according to the instructions in section 7.8.

It is currently possible to set the Baud rate of the digitiser's console port and of the EAM's Port B independently, leading to a loss of data communication between the two modules if the two do not match. If you wish to have a higher transfer rate between the two modules, both ends must have their Baud rates increased separately. The digitiser module's Baud rate must be changed first.

Port C of the acquisition module is used for synchronisation and can either provide NMEA to the digitiser module or share incoming GPS data from an external receiver. Different internal connections are used in each case: an analogue switch is controlled by the service selected for the EAM's Port C.

When the Port C service is set to “NMEA In”, the connections are as follows:

Note: this configuration is not recommended as a method of synchronising a acquisition module (see section 9 for a detailed explanation).

Incoming data from an external GPS receiver is available to both the digitiser and acquisition modules. Both the digitiser's GPS input and Port C of the acquisition module must run at 4,800 Baud. This should never be changed.

If an external GPS receiver is available, it should be used to synchronise the digitiser: the EAM should then be synchronised the digitiser's RTSTATUS packets. In this case, the service on Port C can be set to “none”.

If use of a GPS receiver is impractical but internet-derived NTP synchronisation is available, this can be used as the clock source for both the digitiser module and the acquisition module. By setting the service on Port C to “NMEA out”, the following connections are enabled:

Both the digitiser's GPS input and Port C of the acquisition module must run at 4,800 Baud. This should never be changed. Note that, in this mode, the external GPS socket is disconnected: it cannot be used as an output for additional digitisers.

15.1.2 Variable Gain Inputs

The cylindrical digitiser is fitted with a programmable gain differential input amplifier which can be set to ×1, ×2, ×4, ×8, ×16, ×32 or ×64 gain operation.

The gain can be set individually for each input channel, either using the Platinum web configuration interface or directly from the digitiser's command line. In either case, the digitiser module must be re-booted before the new value will take effect.

The gain settings are reported in the status stream at boot time:

ADC #1 Version 760303
ADC o/s nulls 0 0 0 0
4 channel system
Gain Control : E8
Gain settings :  Ch#0 *1  Ch#1 *1  Ch#2 *1  Ch#3 *1

In the example above, all channels are set to unity gain (channel 0 is the vertical component and 1, 2 and 3 are the North/South, East/West and auxiliary/calibration channels, respectively. On a seven-channel digitiser, channels 4, 5 and 6 are the vertical, North/South and East/West components for the second instrument). If variable-gain-aware firmware (v106b42 and above) is loaded on a digitiser without variable-gain hardware, the text “No gain stage” will appear in this position in the boot status stream.

The selected gain setting is encoded into the GCF headers by appropriating bits from the System ID which must, therefore, be chosen to be five (or fewer) characters long. See the note at the end of this section for more information. The InfoBlock should be changed to reflect the amended System ID but the gain figure taken from the calibration document should be used unchanged, regardless of the variable gain setting chosen. Similarly the “calvals” file in Scream should not be changed, other than to reflect the System ID; Scream can deduce the variable gain settings in use from the GCF block headers and automatically take account of these during calibration operations.

To change the gain using the web interface select:

Now select the digitiser from the list. Once connected, scroll down to the Connected devices. The following section appears:

(This table is extended to show three additional components when a seven-channel digitiser is detected.)

From here, the gain can be set individually for each component. If the button is clicked, the changes will be stored in the digitiser module's configuration but will not take effect until the module is rebooted. If an immediate change is required, the button should be used instead.

To change the gain using the command line, use the data-terminal command to connect to the digitiser, as described in section 8.2 and issue one of the following two commands.

To simultaneously set all channels to the same gain, enter the command:

gain *gains

where gain is one of 1, 2, 4, 8, 16, 32 or 64. For example, to select ×8 gain on all channels, enter the command

8 *gains

The digitiser must be rebooted before the change will take effect.

To set the gain for an individual channel, enter the command:

channel gain *gain

where channel is one of 0 (vertical), 1 (North/South), 2 (East/West) or 3 (auxiliary/calibration). On seven channel digitisers, this parameter can also be one of 4 (vertical), 5 (North/South) or 6 (East/West), referring to the components from the second instrument. gain is one of 1, 2, 4, 8, 16, 32 or 64. For example, to select ×16 gain on just the vertical channel, enter the command

0 16 *gains

The digitiser must be rebooted before the change will take effect.

Software developers working with GCF packets can decode the selected gain setting from the GCF header as follows:

If the most significant bit of the System ID is zero, variable gain is not used. If the most significant two bits of the System ID are 10 or 11, the next three bits encode the gain, using this code:

Bits 2, 3 & 4

Gain

000

not fitted

001

×1

010

×2

011

×4

100

×8

101

×16

110

×32

111

×64

15.1.3 USB operations

The Cylindrical Digitiser can behave as a USB storage device (via the GPIO connector) or as a USB host (via the USB connector).

15.1.3.1 USB device mode

The Cylindrical Digitiser is fitted with an internal Flash memory device which is accessible via USB. It can be written to by selecting “Internal USB storage” from the “Recording destination” drop-down menu on the “Disk recording” page (see section 11.2).

When a USB host, such as a laptop or PC, is connected to the GPIO port (who's pin-out is given in section 16.5.6) internal circuitry detects the USB power and automatically connects the Flash memory to the GPIO socket, causing it to behave identically to a standard USB memory stick.

When no power is detected at the GPIO port, the Flash memory is available to the system as if it were a standard removable mass storage device. All of the mass storage device recording options described in section 11.2 (on page 140) will apply to this device.

15.1.3.2 USB host mode

If a USB storage device is connected to the USB port (see section 16.5.8 for the pin-out), it will be mounted under /media. It can be used to store seismic data by selecting “External USB drive on mil-spec connector” from the “Recording destination” drop-down menu on the “Disk recording” menu (see section 11.2).

15.2 DCM

The DCM is a fully-functional, Linux-based computer system especially designed for handling seismic data. It can collect and store data from several sources and, if required, output it in your preferred format to other locations on your network or on the Internet. The CMG-DCM receives data from one or more of the following sources:

All the received data are stored in files in the on-board Flash memory. There are two banks of Flash memory available, which are accessible as /nand0 and /nand1 in the Linux file tree. Data are normally stored as GCF (Güralp Compressed Format) files.

As an option, you may be able to configure the DCM to use the miniSEED or sac formats instead.

In automatic mode, when the Flash memory becomes more than 75% full, the oldest data files are moved to the DCM's primary hard disk until it is less than 50% full. If you prefer, you can configure the DCM to write to the hard disk at set intervals.

Writing to the hard disk is performed robustly, so that no data will be lost if a write is aborted. This means that you can safely swap hardware in and out at any time. Stand-alone DCM modules use off-the-shelf Lacie hard disks, which can be easily removed and installed in most conditions. You can specify other models of IDE / USB or IEEE 1394 2.5” disk at manufacture. If an internal disk is not present, and the module has a USB host interface, it will look for hard disks connected to its external USB port.

Once the data are stored on the DCM, whether in Flash memory or on the hard disk, it can be retrieved by

A PC running Güralp Systems' Scream software can not only collect data from the DCM, but also configure the module and any instruments attached to it.

You may need to enable and configure some of these methods before you can use them.

Most installations of the DCM will not require any more complex setting up than the Web configuration system can offer. However, in some cases you may need to take advantage of the flexibility offered by the underlying Linux operating system.

For more information on using and configuring the CMG-DCM see the manual MAN-DCM-0001.

15.3 24 Channel DAS

The CMG-DM24S24EAM comprises an EAM, interface board and 4 DM24 digitisers.

Originally built to process geophone signals, the DAS uses a system of breakout boxes to transmit the analogue signals to the module. The Pelicase and breakout boxes are shown in the images below

Each of the four breakout boxes has terminal connectors for up to 6 channels and connects to the DAS using 32 pin mil spec connectors.

Other ports on the DAS are: Data out, Ethernet, USB and GPS and triggering.

For more information on the ports see section 2.5. The connector pinouts are the same as those for the Cylindrical Digitiser and are are given in 16.5 on page 275 and listed in the table below:

Port

Section

Sensor

Section 16.5.14

Data

Section 16.5.2

Ethernet

Section 16.5.4

USB

Section 16.5.3

GPS

Section 16.5.7

The system architecture is detailed in the image below:

15.4 Instruments with integrated CMG-EAMs

Güralp Systems digital instruments, such as the CMG-5TDE (shown below), have an integrated digitiser and EAM.

The internal connections between the CMG-DM24 modules and the CMG-EAM module are identical to those in an Cylindrical Digitiser, as described in section 15.1 on page 252.

For more information on the ports see section 2.5. The connector pinouts are the same as those for the Cylindrical Digitiser and are are given in 16.5 on page 275 and listed in the table below:

Port

Section

Data

Section 16.5.11

Net

Section 16.5.4

GPIO

Section 16.5.6

USB

Section 16.5.8

GPS

Section 16.5.10

PreviousNext

1. Preliminary Notes 2. Equipment Overview 3. Initial set-up 4. Platinum Overview 5. Platinum Firmware Upgrades 6. Data Handling 7. Networking Configuration 8. Digitiser Configuration 9. Digitiser Synchronisation 10. Receiving Data 11. Recording and Retrieving Data 12. Transmitting Data 13. Building Networks 14. Monitoring Operations 15. Technical operation 16. Appendices 17. Revision history