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here, in 0 time & 0 style, we'll try to serve you some interesting ressources, statements, manifests, study's, archives and other stuff that might help you to get . . . totally lost!
image (c) Bert Lezy
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image (c) Bert Lezy
Thursday, May 06, 2004
The Zero-Time Myth
Only the factories have the legal right to declare an engine "zero time." As Coy Jacob explained recently in Aviation Consumer, that doesn't mean all new parts. A zero-time engine can contain used parts -- perhaps many used parts of unknown service history. Here's what you're really getting for your flying dollar.
by Coy Jacob
Zero Times Infinity
Setting the Zero Time
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By default, the Telemetry Toolbox uses the absolute time provided in the sample time tags to label the horizontal axis in time plots and when creating labels for data points and data ranges. This is appropriate for many applications, but in some situations it is preferable to reference the time tags of data samples to the time of an event. For example, it may be desirable to reference the time sequence of a missile flight to the time of missile launch. The Telemetry Toolbox makes it easy to identify a time reference event, called the zero time, and locate this time for each data file as it is loaded.
The zero time is specified by placing an expression in the Zero time field of the Telemetry Toolbox Dictionary Editor. The dictionary editor is opened with the command tmedit(dictionary_name). The zero time expression must evaluate to an object of the tmtime class containing the desired zero time.
The recommended approach for preparing zero time expressions is to first identify the conditions within the data that become true at the desired zero time and at no earlier time. For example, suppose the telemetry variable named launch goes from 0 to 1 at the desired zero time and is required to be zero during the entire period from the start of the data sequence until it transitions to 1 at launch.
The next step is to develop an expression that is zero until the desired zero time and then becomes nonzero. A number of logical operators can be combined to produce this result. For this example, the expression could be the launch variable itself, or the expression launch==1 would work as well. Note that the expression launch==1 results in a tmsignal object with the same number of samples as the launch variable and contains the results of the equality comparison in each sample.
The final step is to convert the time that the expression becomes nonzero into a tmtime object. This operation is performed by the tmsignal/timeof function. The statement t = timeof(s1) determines the time of the first nonzero sample in the tmsignal object named s1. The return value t is a tmtime object containing this time. For this example, the complete expression placed in the Zero time field of the dictionary editor would be as follows.
timeof(launch==1)
After entering the zero time expression, click OK in the dictionary editor to save the dictionary and close the dictionary editor.
Ok?
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