Instrument Parameter Data Window

This window is accessed from the Main Window, using the drop-down list for the Instrument. It is for inspecting and editing the extra parameters associated with an instrument that are not included in the GCF data stream. All information is optional, and is not required for proper operation of Scream.

Scream can use up to three different files when searching for parametric information for instruments. This window allows the user to control what parameters are in these files, and optionally copy entries between files. The three files are defined as:

• The file referenced by the ParametersFile= entry in the [custom] section of the "scream.ini" file.
• A file called calvals.txt in the current directory. In Windows, the user can most easily control the startup current directory by editing the "Start in" property of a shortcut to Scream.
• A file called calvals.txt in the same directory as the Scream program executable.

Scream will search the above files, in the listed order, for an entry that matches the instrument's ID. If found, Scream will use any information in the entry that it recognises.
For a typical installation, only the last file will exist, and this is the file that will normally be used.

The first option (the "ParametersFile" specification) can be used in situations where multiple computers are running Scream on a network, are receiving the same seismic data, and wish to have a single, centrally maintained Parameter File. In this case, a parameter file would be placed on a network file server, then each client Scream installation would be modified so that the ParametersFile value is pointing to the network shared file.
The second option is sometimes useful to start the same Scream program, but use different calvals.txt files. Another use of the second option is if security permissions prevent write access to the location where the executable is kept.
The thrid option is the default for most installations.

When the window first opens, Scream will scan the files in the above order, and if it finds an entry matching the instrument ID, will copy the information into the edit box. It will also set the Parameter Data From and Parameter Data To lists to the file name.
If you change the Parameter Data From selection, then the entry (if any) of that file will be copied into the edit box, and the Parameter Data To selection will change accordingly. In this way, the default behaviour is that any changes are saved to the same file the entry came from. To copy an entry from one file to another (e.g. from a local file to the network file), first select the "source" file in the Parameter Data From selection, then select the "destination" file in the Parameter Data To selection, then click the "Save" button.

The user is free to store any text data in the parameter files, but Scream is programmed to recognise and use some specific entries, as follows:

G=n1,n2,n3	'n1','n2','n3' are numbers representing the gain of the sensor, Z,N,E channels respectively. For an accelerometer, the gain is in units of V/m/s². For a velocity instrument, gain is in units of V/m/s
VPC=v1,v2,v3	'v1','v2','v3' are numbers representing the Volts Per Count of the digitizer, Z,N,E channels respectively. The units are µV/count
RESPONSE=s1 s2	's1' is a string describing the response of the instrument. This value is used by some addons (eg. ART) as a lookup for the transfer function poles and zeros. Typical values for velocity instruments would be "30s", "120s", "360s", etc. A typical value for an accelerometer might be DC100 (meaning the response is from DC to 100Hz). 's2' is either "acceleration", "velocity" or "displacement". This is used to determine the units of the "G" variable above.
GRAVITY=g	'g' is the local acceleration due to gravity. This value is optional - if omitted, Scream uses a default value of 9.80665. This value is used to scale acceleration plots if the user has selected units of g for display.

Other entries that may be used are:

TYPE=s	's' is a descriptive string used to identify the instrument type. e.g. "CMG-3T", "CMG-5TD", etc. Some software packages may display this text on graphs or plots.
COILCONST=c1,c2,c3	'c1','c2','c3' are numbers representing the Coil Constants of the sensor, Z,N,E respectively. These values are required for interactive calibration operations. For an accelerometer, c1=c2=c3=1.
CALVPC=v1	'v1' represents the Volts Per Count of the calibration channel. That is, the digitizer input that records the calibration input signal. The units are µV/count
CALRES=r	'r' is the calibration resistor value, in Ohms. For velocity instruments, this value is published on the calibration documents, and is normally 51000. For accelerometers, this value should be 1.

Scream uses the VPC, G and RESPONSE values to auto-scale the streams in a WaveView Window to indicate physical units. Units of scaling are set in the Display page of the Setup Window.

If a digitizer has it's "Info Block" loaded, and if that block contains parameter=value type lines (as above), then these lines will be automatically extracted by Scream, and saved in the relevant calvals file. This information will then automatically be available for further use. For more information on the Info Block, please refer to the digitizer documentation.