MREL DATA TRAP II, Operation Manual

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DataTrap II™ Operations Manual - Edition 5.4
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4.1 Information on Memory and Triggering
4.1.1 Memory
The DataTrap II™ Data/VOD Recorder has a large circular memory containing either: 64 million, 128 million or 256 million data points,
depending on the Memory Option installed. These data points are allocated according to the number of tests in which the DataTrap II™
Data/VOD Recorders memory has been divided, and the number of Channels being recorded. These values, for a selected Recording
Rate, define the available Total Recording Time for each test. Selection of the number of tests to be recorded, the number of Channels
and the Recording Rate is done using the Software as detailed in the DAS™ Data Acquisition Suite Manual . The DataTrap II™ Data/VOD
Recorder Software automatically calculates and displays the Total Recording Time per Test and the Pre-Trigger Time . The exact amount of
memory allocated to a particular channel for a particular test can be adjusted.
The typical usage of the DataTrap II™ Data/VOD Recorder is to set it up by choosing the number of tests and channels, which divides
memory equally between them. After that, sizes can be increased or decreased for specific tests and channels. For planning a sequence
of tests, the following equation is useful:
A general equation to calculate the Total Recording Time (Pre-trigger Time + Post-trigger Time) is:
Total Recording Time (seconds) = P / [(# of tests) x (# of channels) x (recording rate)]
Where P=# of points currently set up in the DataTrap II™ Data/VOD Recorder = 64, 128, or 256 million
Note: because of binary rounding (1 megabyte = 1.048 million bytes), the actual number of data points is 67 million, 134 million, and
268 million.
If the number of tests selected is one, and only one channel is being recorded, the available recording time will be maximized for a given
Recording Rate. For example, at the maximum Recording Rate 10 MHz, and a
DataTrap II™ Data/VOD Recorder with maximum memory,
the Total Recording Time will be:
268,000,000 / ((1 test) x (1 channel) x (10,000,000 points/sec)) = 26.8 seconds
For 8 channels, it is,
268,000,000 / ((1 test) x (8 channels) x (10,000,000 points/sec)) = 3.3 seconds
When using precise adjustment to set up a channel, the length of test can only be increased or decreased 1024 points at a time.
Pre-Trigger time can be adjusted to an exact number of points.
4.1.2 Triggering
When the trigger type is selected in the Software to be External, the trigger signal that the DataTrap II™ Data/VOD Recorder receives is
from the Trigger Wire . This corresponds to time = 0 on the resulting VOD graph.
When the trigger type is selected in the Software to be Internal and set to Low Level the DataTrap II™ Data/VOD Recorder is triggered
This Chapter provides information on the memory of the DataTrap II™ Data/VOD Recorder and
triggering.
Overview