MTS Series 793 Application - Manual (Page 278)

MTS MultiPurpose TestWare® Data Acquisition Process Descriptions 278
Time and Rollover
Time signals
Time and Running Time signals are useful for recording the duration of tests.
They may also be useful for providing a time reference for data acquisition for
tests of short duration. However, as the length of a test increases, their suitability
as a time reference for data acquisition decreases. This is because Time and
Running Time are floating point numbers, and their resolution decreases as they
increase in value.
For instance, when the Time signal runs continuously for approximately six
months (2
24 , or 16,777,216 seconds), its resolution drops to one second—which
is far too course to be used as a time reference at typical data acquisition rates.
To obtain a time reference with suitable resolution for longer tests, use Rollover
Time or Running Rollover Time. These signals are also floating point numbers,
but they rollover (reset to zero) every hour (3600 seconds). This maintains a high
resolution with respect to typical data acquisition rates. However, because
Rollover Time and Running Rollover Time reset to zero every hour, they lose
reference to where they occur within the test.
It is possible to obtain a composite time reference that has the desirable
characteristics of both Time and Rollover Time. To do this, select both types of
signals for the data acquisition process (Time and Rollover Time), run the test,
then open the data file in a spreadsheet application, such as Microsoft Excel.
Next, use the spreadsheet application’s math functions to derive a new column
derived from the Time and Rollover Time values in each row, as follows:
composite time = INT(Time/3600) x 3600 + Rollover Time
Where INT (Microsoft Excel syntax) rounds down the result of Time divided by
3600 to the nearest integer.