Currently, there are no user options that affect the size of the SIE file. The data types used for channels are set to minimize CPU load, which means that 64 bit floats are used for all channels where any numerical processing is required. The only exception to this are the MX channels that source data as 32 bit floats, with no numerical processing required. This includes the MX840 CAN channels. However, the MX471 CAN channels are currently stored as 64 bit floats.
NOTE
Providing user options for storing channels in other data types to consume less SIE storage area is planned for the future, but is not scheduled at this time.
Users commonly want to know how long a test can run before it fills up the SIE storage area or reaches a maximum desired SIE file size.
When the system is used in a simple “channel data logger” mode where all channels are stored using the Collect time history storage option (or one or more Time History DataModes configured to use the Always on triggering option), this can be calculated with reasonable accuracy using the following steps.
bytes_per_second = bytes_per_sample * sample_rate * overhead_factor
if (sample_rate >= 50) block_time = 5;
else if (sample_rate >= 10) block_time = 10;
else if (sample_rate >= 2) block_time =20;
else if (sample_rate > 0.4) block_time = 40;
else block_time = 80;
bytes_per_block = sample_rate * block_time * bytes_per_sample;
if (bytes_per_block > 8000)
bytes_per_block = 8000;
else if (bytes_per_block < bytes_per_sample)
bytes_per_block = bytes_per_sample;
overhead_factor = (bytes_per_block + 40) / bytes_per_block;
NOTE
The “block_time” parameter in the above algorithm is the time between block write to the SIE file. For example, at 50 S/s, blocks are written every 5 seconds, and at 1 S/s, blocks are written every 20 seconds.
Of course, it is common for the system to be used in a more complicated mode than a simple “channel data logger”.
NOTE
The histograms are stored in DRAM memory while the test is running. They are written to the SIE file when the test is stopped. SIE storage space is reserved for this to ensure they can be stored, even if the SIE storage area is fully consumed during the test.