Contents Page

Astronomy

Asteroid Occultations

Lunar Occultations

TESTING THE McAFEE VTI

On this page I have endeavored to test the McAfee VTI GPS time inserter that I use to time astronomical events, namely Lunar and Asteroidal Occultations. This is to attempt to glean the accuracy of the timestamps inserted onto the videotape in relation to Universal Time.

To this end, I videotaped the blinking LED. Below you will find a Excel chart of the LED turning ON and OFF. LiMovie was run in “FIELD MEASURE” mode in this example.

(LiMovie needs to be corrected to correctly measure fields. My version does fields backwards, hence the step you see below, which is not real. When the LED is ON, it is on for every field.)

Below is the same data taken from LiMovie while measuring in “FRAME MODE”

Two Complete ON/OFF Cycles in Field Mode

Times for the above 4 events from the Fields View in LiMovie

43.9733           OFF

44.u      ON

44.0250   ON

44.0414   ON

44.4505           ON

44.4672           OFF

44.9742           OFF

45.u      ON

45.0261   ON

45.0424   ON

45.4189           ON

45.4352   OFF

OBSERVATIONS

1.     Limovie needs to be corrected to measure fields in the correct order…

2.     McAfee VTI can time fields very well..

3.     Absolute times at the second marker display incorrectly. ***Does 45.u equal 45.0000 ????*** SEE BELOW

4.     These two events are of differing duration. The event on the left covers 30 fields, the one on the right covers 28 fields.

5.     Math shows the two “R’s” as 44.0086 and 45.0097

6.     44.0086 = 0086 times 0.000102 = .008772 seconds - .008 = 44.0008s +/- .008s

7.     45.0097 = 0097 times 0.000102 = .009894 seconds - .008 = 45.0019s +/- .008s

8.     Subtract .0167s when viewing frames .. .008s when viewing fields

CONCLUSION

The McAfee VTI is quite good at stamping individual fields with highly accurate times that are easily related to absolute Universal Time. When used in conjunction with other tools, such as LiMovie and Virtual Dub, the Accuracy and Precision are quite high, while the uncertainty is as low as the methods allow.

An Excellent Unit.

Last updated: 05/24/06

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