Guralp Systems Limited
MAN-SWA-0001 Issue M - Scream User's Guide


1. Preliminary Notes 2. Introduction 3. Installation and Configuration 4. Acquiring data 5. The Main Window 6. windows 7. Forwarding data over a network 8. Supplementary windows 9. Configuring CD24 and DM24 digitisers 10. Controlling CD24 and DM24 digitisers 11. Recording and playback 12. Printing options 13. Logging and notification 14. Extending Scream! 15. Keyboard and mouse shortcuts 16. Inside Scream! 17. Revision history

Section Index: 8.1. Terminal windows 8.2. Digitiser status streams 8.3. The summary window 8.4. The ViewInfo window

Chapter 8. Supplementary windows

Aside from the Main Window, WaveView windows and Network control window, Scream! includes facilities for monitoring status streams, the status of your network, the integrity of incoming data, and for accessing the serial consoles of attached DM24 and CD24 digitisers.

8.1 Terminal windows

Scream! provides a terminal emulator that can be used over both serial lines and networks. It can open a network terminal session with any connected CD24 or DM24 digitiser. Over a serial link, it can, In addition, open a session to the command line of an EAM if the server permits it: see Chapter 7.

8.1.1 Communicating with instruments

To open a terminal session with an instrument, right-click on its entry in the left pane of Scream's Main Window and choose Terminal… from the pop-up menu:

Scream! automatically negotiates with any other Güralp devices or software in the chain until it reaches the one you want to contact, and then attempts to place the target digitiser in command mode. If this fails, press + in the Terminal window to enter command mode manually.

If you see an ok prompt, as shown below, the digitiser is ready to receive commands. Otherwise, press to display a prompt. You can now type terminal commands into the window.

The + and + arrow keys let you browse through the history of typed commands. This history is common to all Terminal windows, so you can easily (for example) send the same command to several digitisers in turn.

To begin capturing a session, including every command you type as well as the instrument's response, right-click in the Terminal window and select Capture to File…. All subsequent actions will be saved to a file with name that you enter, combined with a unique source string. Capturing stays in effect through digitiser restarts and, also, if you close Scream! and restart it later. The capture file's name is displayed in the caption of the Terminal window.

To send a file to a digitiser, right-click in the Terminal window and select Send File…. In Windows, you can also drag-and-drop a file. This can be used to read in lists of commands that you have prepared; for example, to set up a number of digitisers identically. It is also used to update a digitiser's firmware.

Note: For details on how to set up firmware transfers, refer to the documentation for the relevant digitiser.

To close the connection, close the Terminal window. Scream! will automatically instruct the digitiser to start transmitting data. If the digitiser begins transmitting data whilst the Terminal window is still open (e.g. because you have issued the close or go command, or because of a time-out), the window will close automatically with the message Terminal session closed by instrument.

8.1.2 Macro commands

The Terminal window provides icons for the keys , which can be programmed with commonly-used commands (“macros”). To define such a macro, right-click on an Fn icon, and enter the command (or commands) in the text box.

You can enter these commands by

Scream! remembers all of your macro settings when you close the program.

8.1.3 Direct connections

You can also open a terminal session directly to your computer's serial ports or over a network. This is useful for communicating directly with modems, or with the consoles of third-party equipment.

To do this, select File → Terminal… from Scream's main menu:

The Select Port to open window is displayed.

The terminal window will then open as described above.

8.2 Digitiser status streams

Most Güralp digitisers have a separate stream for reporting information about the system, such as their GNSS and time synchronization status. This status information is in plain ASCII text format.

To see a Status window for any digitiser, double-click on the Stream ID which ends with two zeros: xxxx00. This stream always has a reported sample rate of 0 samples per second.

During boot-up, each unit reports its model type, firmware revision number, its System ID and its serial number via this stream. This information is followed by the number of resets that have occurred and the time of the latest reboot from its internal clock. The following lines report the current configuration of the unit's sample rates, output taps, and baud rates.

A typical digitiser re-boot status message looks like this:

The system will produce a similar status message whenever it is powered up and whenever you reboot it (for example, after changing its configuration).

Various status messages will be highlighted in red or green depending on the importance of the message (e.g. the “System Boot” message above). The right-click context menu offers a Custom highlighting... option that allows user-definable key words or phrases to cause a status line containing that phrase to be highlighted red or green, depending on the list into which it is entered.

8.2.1 GNSS

GNSS is the general term for a Global Navigation Satellite System. It can refer to one or more of GPS, GLONASS, Galileo, Beidou etc. In this document, the term GNSS is also used to refer to the receiver module that is connected to the digitiser.

If a GNSS receiver is connected to the digitiser, its operational status is reported on reboot and the behaviour of the time synchronisation software will also be shown.

From a cold start, the GNSS receiver will initially report No GPS time together with its last position (taken from the internal backup). All messages from the GNSS that involve a change of its status are automatically reported. Some digitisers will suppress small changes in reception strength once a 3D fix has been obtained.

A typical GNSS status report from a DM24 digitiser looks like this:

This report shows which satellites (officially: Space Vehicles, abbreviated to SVs) the system has found, along with their corresponding signal strengths.

If the system has not been moved from its previous location, it should be able to find enough satellites to obtain an accurate time fairly quickly; if the GNSS receiver has difficulty finding satellites, there may be a delay of several minutes before a new message is displayed.

Before beginning to synchronise, the digitiser's internal clock management software will wait for the GNSS receiver to report a good position fix from at least three satellites, for at least six consecutive messages. Messages are normally received every 10 to 20 seconds.

The system will then set the internal clock and re-synchronise the Analogue to Digital Converters so that all subsequent data are accurately time-stamped to the new reference.

Note: Any data transmitted up to this point will have been stamped with the time from the internal, battery-powered backup clock, which can be significantly inaccurate if the digitiser has been powered down for a long time.

The re-synchronisation will result in a discontinuity in the data received. If you are viewing the data in a WaveView window and the status stream is also being received and block markers are enabled, the resynchronisation will be marked in the WaveView window with the symbol. See section 6.1.7 for more information.

From this point, the control process in the digitiser will attempt to keep the internal time-base synchronised to the GNSS' 1 pulse-per-second (PPS) output, by adjusting a voltage-controlled crystal oscillator. First it alters the voltage control to minimise the error. Next it attempts to minimise both the “phase error” (i.e. the offset between the internal 1 Hz signal and the GNSS) and the drift (the frequency error relative to GNSS, which is the first derivative of the phase error). During the control process, the system reports the measured errors and the control signal applied as the PWM (Pulse Width Modulation) value.

During the initial, coarse adjustment stage, only the coarse voltage control is used and no drift calculation is made. If the system is operating in a similar environment to that when the system was last powered (most importantly, the same temperature), the saved control parameters will be appropriate and the system should rapidly switch to the ‘fine’ control mode. The system reports its control status and parameters each minute, with error measurements given in nominal timebase units. In a stable temperature environment, the system should soon settle down and show an offset (error) of only a few thousand (average error < 100 microseconds) and a drift rate of under a hundred counts (< 1 in 10-6).

8.2.2 Graphing status information

Most Güralp digitisers transmit a status block every few minutes, giving information about the GNSS status, internal temperature etc:

Scream! can automatically extract measurements from these messages and show them in graphical form. For each plotable field that Scream! finds, amcheck-box is displayed at the top of the Status window. In the example above, Scream! has found Offset, Drift, PWM, Volts (i.e. DC input) and Temp (temperature) fields in the status messages. Not all digitisers output all of these fields, so some of these check-boxes may not be present in all windows.

Note: Scream determines that a field is present only once it has seen the relevant value appear in the status stream. It may be many minutes before a given parameter, such as Temperature, appears. Scream will not offer the ability to graph such a value until it has appeared at least twice.

To display any or all of these fields in graphical form, tick the check-box(es) for the field(s) you want to examine:

You can resize the Status window, or drag the bar between the graphs and the block display area, to see the graphs in more detail.

8.2.3 Station Lat/Long

Some digitisers will periodically report the Latitude and Longitude of the GNSS receiver coordinates in the status information. For example

2017 6 14 09:00:00 Lat 51'21.6718N Long 001'09.8555W Height 113m

When detected, Scream will parse these lines, and update an internal record of instrument location.

Scream can use this location information in several ways:

The location information is stored in the calvals data. Entries are automatically created with the name aPos1=. A number of fields in this entry record the details of the location, as follows:




Averaged latitude


Averaged longitude


Averaged height


Number of points received at this location


Date/time of first report at this location, in ISO8601 format


Date/time of most recent report at this location, in ISO8601 format

When a new Latitude/Longitude report is detected in the status, it is compared to the current, known position. If within a small range (default 250 metres), it is assumed that the receiver has not moved so the location is added to the averaged position and the most recent time is updated. In this way, the longer the station runs for, the more readings are averaged, and the more precise the stored location becomes.

However, if the new position is out of this range, the instrument is assumed to have moved, so a new location is started with an incrementing aPos entry (e.g. aPos2= then aPos3= etc). In this way, a history is built up of where and when a particular sensor has been. This can be useful for portable arrays and seismic surveys, where equipment moves regularly.

In some circumstances, GNSS receiver location is not available, or not accurate (e.g. time source is not a GNSS, or is centrally distributed to an array over a large area). To override the automatic position, a manual position entry - mPos= - can be entered in the format shown:

mPos1=51.3132 -1.2243 160.7132

Only fields one, two and three - latitude, longitude and height - are specified in this case.

8.3 The summary window

This window provides at-a-glance state of health information about all instruments on your network. To open it, choose Windows → Summary window from Scream!'s Main Window.

Every instrument known to Scream! is listed in this window, with coloured icons representing their timing, mass position and data flow status. The window also reports how many triggers have been communicated to Scream! in status blocks.

To make Scream! forget this information and start afresh, click . This will not remove streams from the Main Window, the WaveView windows or the stream buffer.

In the leftmost four columns, each entry is a coloured rectangle with a border. A grey rectangle indicates that no relevant data have been received from the instrument since Scream! was started. Green indicates that this measurement is satisfactory; yellow indicates that some attention may be necessary, and red indicates that there is probably a problem.

If a box has a coloured border, an unsatisfactory reading has been received since the last reset, but the status has since improved. Thus, if a box goes from yellow to green, the border will be coloured yellow until you reset. If the same box subsequently turns red momentarily and then returns to yellow or green, the border will change to red.

8.3.1 Timing

This column details the instrument's GNSS timing status. The colours are the same as those used for the top half of the instrument's icon in the Main Window. Double-click on a column entry to see the status messages coming from that instrument.

8.3.2 Mass position

This column indicates the instrument's mass position status. To open a WaveView window showing the instrument's mass position channels, double-click on the column entry.

The status is obtained by comparing the mass positions to the threshold set in the EMail tab of the Setup window - see section 13.2 for details.

8.3.3 Age

This column records the time that the instrument last sent data to Scream!.

When a data block is received, the box turns green. Over the next two minutes, if no more data are received, the box gradually changes through shades of yellow, to orange, and finally red.

If more than two minutes pass before the next data block is received, the border of the box will change to red to alert you that a suspicious gap in data has been detected. If you do not expect real-time data from this instrument, or you are using low sample rates exclusively, you may allow this column to turn red. For example, a one sample per second stream will transmit a block only once every four minutes under quiet conditions.

Double-click on a column entry to select the instrument in Scream!'s Main Window.

8.3.4 Errors

This column records the number of corrupted blocks that Scream! has received. A corrupted block is one whose checksum does not match the data, or which fails one of Scream!'s integrity checks. To see which checks are failing:

The meaning of the colours is as follows:

8.3.5 Triggers

This column records the number of times the digitiser has sent a trigger status message since Scream! was started. New triggers are coloured in green; when you Reset window, the green shading will disappear, but the number will remain.

Double-clicking on a column entry opens a window with details of the trigger events:

The top half of the window lists all the trigger events, with information extracted from each trigger's status message. The full status message is reported in the lower half.

Double-clicking on an entry in the table (or selecting it and pressing ) opens a paused WaveView window containing all of the streams from the digitiser which declared the trigger, covering the time period of the trigger. This time period is marked with the Time Cursors to show the duration of the event.

If you have instructed the digitiser to record pre- or post-trigger data, Scream! will attempt to include these as well. If two triggers from the same digitiser overlap, Scream! may show both triggers in the WaveView window, because the point where one trigger ends and the next begins is essentially arbitrary.

Scream! can only display data which is still in its stream buffer. If the buffer is full and the data have already been purged, double-clicking on a trigger will show a blank window. To view the data, you will need to retrieve it from the hard disk or your recording system and replay it into Scream!.

The columns contain the following information:

Start : The start time of the trigger, prefixed with a * if the trigger occurred since the last time you reset the Summary window.

End : The end time of the trigger.

Type : What caused the trigger: R if the STA/LTA ratio exceeded the set threshold, L if the level exceeded the threshold, E for an external trigger (if the digitiser supports it) or S for a manual trigger (generated in software).

You can also open the Triggers window by right-clicking on a digitiser's entry in the Main Window and selecting Triggers… from the menu.

8.4 The ViewInfo window

Detailed header information from incoming data blocks is available from the ViewInfo window, accessible by selecting Windows → Info Display… from Scream!'s Main Window.

If ALL is selected as the Source at the top of this window, details of every incoming data block will be shown as they arrive. You can narrow the selection to a particular source using the drop-down menu.

Scream! makes a number of validity checks for incoming blocks. Any suspect fields are shown in red in the ViewInfo window.

When analysing data received over BRP (i.e. from all serially connected digitisers and network-connected CD24s), the first three fields and the final Checksum (Cksum) come from the transport header, which is added to each GCF block to aid with data transmission. When analysing data received over the network using the Scream! protocol, these values are synthesised.

The displayed fields are:

The remaining fields constitute the information available from the GCF block's internal header and mostly duplicate the information available in the stream list. The following additional information is available:

Scream! also logs any errors that it detects. For more information on Scream!'s logging system, see Chapter 13.


1. Preliminary Notes 2. Introduction 3. Installation and Configuration 4. Acquiring data 5. The Main Window 6. windows 7. Forwarding data over a network 8. Supplementary windows 9. Configuring CD24 and DM24 digitisers 10. Controlling CD24 and DM24 digitisers 11. Recording and playback 12. Printing options 13. Logging and notification 14. Extending Scream! 15. Keyboard and mouse shortcuts 16. Inside Scream! 17. Revision history