To control a digitizer whilst it is running, either right-click on the digitizer's entry in the list to the left of Scream!'s main window (not the Local or Comxx icons) and click Control..., or simply double-click the entry. Scream! will then contact the digitizer and retrieve its current status, a process which will take a few seconds, after which the Control window will be displayed. Once you are happy with any changes you have made in the Control window, click Apply to send them to the digitizer, where they will take effect immediately.
If you cannot find the setting you want in the Control window, it may be because the digitizer needs to reboot after a change. Look in the Configure window instead.
When the Control window is first opened, it will be showing the System pane.
Sensor Type : If the sensor attached to the digitizer is a Güralp velocity sensor, you can send control commands to it from the Mass Control tab (see below.) Which functions are available on this tab depends on the Sensor Type you have set here.
If you change the Sensor Type, you may have to Apply the change, close the Control window, and open a new one to access the Mass Control options.
Enable GPS power cycling : If you are using a GPS unit to receive time signals, but do not experience significant drift in the system's clock (for example, in a stable-temperature environment), you can save power by selecting Enable GPS power cycling. With this option in use, the GPS time is only checked at intervals of a specified number of hours.
The Triggering pane is very similar to the corresponding pane of the Configuration setup window, although not all options are available since some require rebooting the digitizer. See Section 6.3, page 72, for more details.
You can check that your instrumentation is correctly calibrated by injecting known signals into the sensor's feedback loop. The Calibration pane allows you to do this once the sensors are installed.
Each channel can be calibrated separately. For most triaxial digital instruments, each channel calibrates the corresponding axis of the instrument; simply select one of the Z, N/S and E/W check boxes to calibrate that axis. Alternatively, click ALL to calibrate all channels simultaneously.
Some instruments use only one calibration loop, which is reproduced for all three components: if you have one of these instruments, you should select Z to calibrate the sensor.
The Duration box tells the digitizer how long to provide the calibration signal before disconnecting. This avoids the system being inadvertently left in calibration mode. The default is 2 minutes. If you change this setting, it will revert to the default value after one calibration stage.
All Güralp digitizers can produce either sine-wave or square-wave (step) calibration signals; newer models can also carry out broadband noise calibration. The Sine wave calibration signal always starts and stops on the zero crossing. The frequency or period given by the boxes at the top right.. Only integers between 1 and 10 may be specified for either frequency or period, so to generate a 0.5 Hz signal you should select Period and set the time to 2 (seconds). Likewise, if you require a 0.25 second period you should select Frequency and set the rate to 4 (Hz). In this manner, you can select frequencies ranging from 0.1 to 10 Hz (10 to 0.1 s periods).
You can specify step calibration by selecting the Square wave button. The square wave consists of a positive step at the start of the next minute of the digitizer’s internal clock, followed by a negative step after a specified number of minutes. After a further delay of the same number of minutes, the calibration signal is disconnected. The default is 2 minutes. The Period and Frequency are ignored.
The Broadband Noise calibration signal consists of a constant stream of white noise, which lasts for the specified number of minutes. The Period and Frequency are ignored.
Many Güralp instruments respond to control signals to centre, unlock, and lock the sensor masses. These signals are generated by the digitizer. You can tell the digitizer to send a signal using the Centre Now, Lock Now and UnLock Now buttons on the Mass Control tab.
If you select Monitor progress, the window will remain open during the process, and the mass positions will be displayed in the Vertical, N/South and E/West boxes. If you leave Monitor progress unselected, the window will close while the operation takes place. You can still monitor mass positions by selecting the appropriate streams and opening a WaveView window for them.
Depending on which Sensor Type you have chosen in the System tab (see above), not all the control signals will be available. For example, CMG-3ESP sensors can be centred from Scream!, but must be locked and unlocked manually, whilst a 3T has remote lock and unlock commands.
CMG-40T, CMG-6T and CMG-5T strong-motion instruments do not need locking or unlocking. If you have set the Sensor Type to one of these sensors, the Mass Control tab will not be available.
The digitizer operates in one of several filing modes. These modes relate to how the unit uses its Flash memory:
as a simple data store, from which you can request data (FILING and DUAL modes);
as a buffer holding unacknowledged blocks, which are transmitted in preference to real-time data (FIFO mode);
as a buffer holding unacknowledged blocks, which are transmitted whenever the channel is free but no real-time data blocks are ready (ADAPTIVE mode);
not at all (DIRECT mode).
Separate from these modes are buffering modes, which tell the unit what to do when its Flash memory becomes full: either
carry on, overwriting the oldest data held, or
stop writing and switch the digitizer into DIRECT mode.
You can switch between filing modes in Scream! by right-clicking on the digitizer and clicking on Control..., then navigating to the Data Flow pane:
To choose a transmission (filing) or buffering mode, choose options from the Transmission Mode or Buffering drop-down menus, and click Apply. An explanation of the chosen mode is displayed beneath each menu. The following sections also explain the filing modes available.
The Buffering legend also displays the amount of Flash memory present in your digitizer.
To clear the Flash memory of the digitizer, click the Reset-flash button. You will be asked for confirmation before the memory is cleared.
At the bottom of the tab is a line describing the current state of the digitizer's memory pointers. You can use this line to check that data is being written into memory. Select Auto-Refresh to make the line update automatically.
Instructs the digitizer not to use Flash memory for storage. Instead, all data is transmitted directly to clients. An instrument in DIRECT mode still honours the GCF Block Recovery Protocol: a temporary RAM buffer always holds the last 256 blocks generated, and if a client fails to receive a block it can request its retransmission.
If you expect breaks in communication between the instrument and its client to last more than 256 blocks, or if you want the instrument to handle breaks in transmission (rather than relying on the client to request missed blocks), you should use
ADAPTIVE mode, if you want data to stay as near to real time as possible (but do not mind if blocks are received out of order) or
FIFO mode, if you need blocks to be received in strict order (but do not mind if the instrument takes a while to catch up to real time.)
Instructs the digitizer not to transmit blocks to clients automatically, but to store all digitized data in the Flash memory. If you have chosen the RECYCLE buffering mode (see below), the memory is used in circular fashion, i.e. if it becomes full, incoming blocks begin overwriting the oldest in memory. If the WRITE-ONCE mode is active, the instrument will switch to DIRECT mode (see above) when the memory becomes full.
When in FILING mode, an instrument transmits “heartbeat” messages over its data port. These short messages take the place of data blocks, and ensure that programs such as Scream! know that an instrument is present.
If your digitizer is in FILING mode, Scream! will displays a slider at the bottom of the tab. Moving this slider changes the interval between heartbeat blocks.
You can tell Scream! to download new data automatically whenever it receives a heartbeat message from an instrument in FILING mode. This is useful, for example, in autonomous installations connected by intermittent modem links. To enable this feature:
Choose File → Setup... from Scream!'s main menu, and navigate to the Recording pane.
Check Auto-upload on heartbeat.
Click OK.
Using FILING mode with Auto-upload on heartbeat ensures that Scream! receives all new data whenever it can, regardless of the configuration of any devices between you and the instrument.
DUPLICATE
Instructs the DM24 to transmit streams directly to clients as for DIRECT mode, but also to store all data into Flash storage as for FILING mode.
If a client fails to acknowledge a block, the digitizer does not attempt to retransmit it.
Heartbeat messages are not sent in DUPLICATE mode.
Instructs the digitizer to transmit any continuous streams directly to clients as for DIRECT mode, but to store triggered data into Flash storage as for FILING mode.
If you choose DUAL mode but do not select any continuous streams for output, the instrument will send heartbeat messages as for FILING mode. Scream! can pick these up and download new data as necessary.
Instructs the digitizer to begin writing blocks to Flash memory as for FILING mode, but also to transmit data to clients. Data is transmitted in strict order, oldest first; the digitizer will only transmit the next block when it receives an explicit acknowledgement of the previous block.
If the communications link is only marginally faster than the data rate, it will take some time to catch up with the real-time data after an outage. If you want data to be transmitted in real-time where possible, but are worried about possible breaks in communication, you should use ADAPTIVE mode instead.
FIFO mode will consider a data block successfully transmitted once it has received an acknowledgement from the next device in the chain. If there are several devices between you and the instrument, you will need to set up the filing mode for each device (if applicable) to ensure that data flow works the way you expect.
Like all the filing modes, FIFO mode does not delete data once it has been transmitted. You can still request anything in the Flash memory using Scream! or over the command line. The only way data can be deleted is if it is overwritten (in the RECYCLE buffering mode, see below) or if you delete it manually.
Instructs the digitizer to transmit current blocks to clients if possible, but to store all unacknowledged blocks in the Flash memory and re-send them, oldest first, when time allows. ADAPTIVE mode is best suited for “real-time” installations where the link between digitizer and client is intermittent or difficult of access.
If the communications link is only marginally faster than the data rate, it will usually be busy transmitting real-time data. Thus, it may take a while for the instrument to work through the missed blocks. In this case, and if your client supports it, you may prefer to use the Block Recovery Protocol to request missed blocks where possible.
Some software packages (most commonly Earthworm) cannot handle blocks being received out of time order. If you are using such a package, ADAPTIVE mode will not work, and may crash the software.
Instructs the digitizer to carry on using the current filing technique when the Flash memory becomes full, overwriting the oldest data held. This buffering mode is called RECYCLE in Scream! and on the DCM.
For example, in DUAL mode with RECYCLE buffering, the latest continuous data will be transmitted to you as normal, and the latest triggered data may be retrieved from the Flash memory using Scream! or the command line. However, if you do not download data regularly from the Flash memory, you may lose older blocks. This mode thus lets you define the end point of the data held by the instrument.
Instructs the digitizer to stop writing data to the Flash memory when it is full, and to switch to DIRECT mode automatically.
For example, in FIFO mode with WRITE-ONCE buffering, the station will transmit data to you continuously, but also save it in the Flash memory until it is full. Once full, the instrument will switch to DIRECT mode and continue transmitting, though no further data will be saved. This mode thus lets you define the start point of the data held by the instrument.