Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 40)

Three functions are available at the Parameter File Operations screen to help the user manage parameter files:
S Save parameters to user-specified file
R Read user-specified parameter file
D Document parameters (create tgaparm.doc file)
The Save and Read functions allow the user to store and recall a particular TGA setup. The Document function creates
file tgaparm.doc, which documents the parameters in a format very similar to the parameter editing screens.
It is very important that the working parameter file, tgaparm.cfg, is not deleted or corrupted. If there is no valid
parameter file when the TGA program is started, a set of default parameters will be used. These defaults are designed to
be non-operational, to protect the laser, and to make it obvious to the user that correct parameters are not in use. If this
happens, restore the parameters, either by reading in a valid parameter file, or by entering new parameters in the
parameter editing screens.
Most of the parameters can be edited using the parameter change screens described in section 3.5, and a subset can also
be edited from the real time screen, as described in section 3.4.4. A complete list of the contents of the parameter file (in
the tgaparm.doc file format) is given in Appendix A.
3.6.2 10 Hz Concentration Data Files
Data are saved by enabling the data collection function (by pressing the <D> Quick key) from the real time screen. This
creates a file called MMDDHHMM.DAT. Normally data are written to the same file until data collection is shut off.
Optionally, new data files can be automatically created at user-specified intervals. This is controlled by Interval to start
new data files (min) parameter in the File Format parameter screen. If this is set to zero, then only one data file is
created. If this parameter is greater than zero, the old file is saved and a new file is created at the interval set by the
parameter.
The user selects which data are saved from the “File Output Selection” parameter menu. Any of the data values that can
be displayed in the real time graphs may also be saved to the concentration file. A complete list of output options is
given in Appendix A.
Concentration data are normally saved every 0.1 second, although it is possible to decimate the data to reduce the size
of the file. This is controlled by parameter “Concentration file decimation factor” in the “File Format” parameter
screen. Set this parameter to 1 to save all of the data, or set it to an integer greater than 1 to decimate the data. For
example, if it is set to 10, only every 10
th sample will be saved (1 Hz instead of 10 Hz).
Two data storage formats are available: ASCII or binary, as determined by the parameter “File format: ASCII (0) or
binary (1)” in the “File Format” parameter screen. The ASCII (plain text) format uses approximately 12 bytes per value.
It is “human-readable” text, and is easily printed or displayed by a simple text editor or spread sheet. Binary format uses
the IEEE floating point standard format. It uses 4 bytes per value, resulting in much smaller files than if ASCII format
is selected.
3.6.3 Gradient (Delta Concentration) Files
Gradient data are saved by enabling the gradient (also called delta concentration) measurement function by pressing the
<G> Quick key from the real time screen. This creates a file called MMDDHHMM.DC, stored in the default data
directory. The gradient measurement mode is discussed in section 5.1.
Data are saved at the end of the sequence. The duration of the sequence is the sum of the Site Time parameters, as
discussed in section 5.1. The time of day (and the day of year) are based on the PC real-time clock, at the time the data
are written to the file. Thus it represents the end of the averaging period. Also, because the timing of the gradient
sampling sequence is driven by the clock in the analyzer electronics, the time of day reported in the file may drift over
time. For example, if the sequence time is 1 hour, the data at the start of the file will be written on the hour, but if the
PC clock is “fast” compared to the TGA100 clock, the data will eventually be written at one minute past the hour, then
two minutes past the hour, etc.
This file is always ASCII (plain text) format. The first four rows contain header information, and the rest of the file
contains the data. The contents of the file are listed in Table 6.
40