Page #1 - Main page with EXTA description

Page #2 - Measurements with analog video camera modul SK1004XC

Page #3 - Measurements with analog video camera WAT-902H2 Ultimate

Page #4 - Measurements with integrating analog video camera WAT-120N

Page #5 - Measurements with Astro CCD camera Atik 314L+

Page #6 - Measurements with IOTA-VTI device (this page)

Page #7 - Measurements with integrating analog video camera MINTRON 12V1C-EX

IOTA-VTI device - Prototye P4

EXTA measurement setup for IOTA-VTI device and analog video camera WAT-902H2 Ultimate

The source for the time stamps in the video images was the IOTA-VTI which was synchronized to UTC with NMEA 0183 data sentences and 1 PPS signal supplied by the internal GPS modul board GlobalSat EM-406A. The analog CCIR video camera used was the WAT-902H2 Ultimate. And the digitizer used was a DFG/USB2-lt Videograbber device from The Imaging Source. The videograbber was connected via USB2.0 to a notebook running with a XP32 system. The capture software was VirtualDub. The CCIR video file was recorded uncompressed and lossless in Y800 format and in container format AVI direct to the harddisk.

The VTI tested here was the recently (2010/11) developed IOTA-VTI device which was presented first to the public in May 2011. The device in test is numbered as prototype P4 and was sent to me in May 2011 for testing by Dave Gault in Australia. Many thanks to Dave for this. The software running in this IOTA-VTI is V1.1.40 which was the current version in May 2011.

The main goal of the test measurements with EXTA was to show the timing behaviour of this IOTA-VTI device in detail. It is very important to know if the time stamps on the individual video fields match exactly the optical exposure times of the video fields. This is not the case on all VTI devices available on the market around the globe. But this would not be a big problem if an existing time shift value is also well known and so can be used to calculate the right exposure times.

Full frame video image with IOTA-VTI time stamp

CCIR video image with IOTA-VTI video time insertion

In this full frame CCIR video image above with IOTA-VTI video time insertion we can see on the right top seconds LED matrix that the exposure started in UTC second 08 and ended within the same second. The same UTC second was inserted by the IOTA-VTI in numbers on the bottom of the video frame. EXTA was set to mode 0 so every LED in the big LED matrix corresponds to 1ms. The exposure startet in the 514th millisecond in the UTC second 08. The end of the exposure can be seen in the 554th millisecond of UTC second 08. If we count all the lit 1ms LEDs we get 41. But if we take a closer look at the LEDs we can see that the first and the last LED of the lit row are a little bit smaller than the others between them. So we can assume that this LEDs were not exposured for a full millisecond. And the over all exposure time may be a little bit over 40ms but surely not 41ms. This result matches with a full length exposured CCIR video frame.

Now if we compare the time measured by EXTA 08.514 - 08.554 and the times 08.5336 - 08.5536 inserted by the IOTA-VTI Video Time Inserter we can see a difference smaller than one millisecond. What is the reason for this difference? The answer is a time shifted output signal of the video camera. The start of the optical exposure is nearly one millisecond late to the output signal of the previous field with Vsync. And because this VTI and most others too are time stamping the video fields triggered by the Vsync we get times shifted smaller than one millisecond. So this time shift is not caused by the VTI device and was also measured by me with my other measurement device VEXA some years ago. But this relative small time shift is absolutely no problem in normal occultation work.

The hour glass symbol displayed beside the P9 is to remind that more than 3 hours has elapsed since the last power on and that the almanac might be in error. This could result in a time error in the seconds range. But if this would have been really the case during this EXTA measurements, it surely would have been visible in the results. Of course for normal occultation work it is better to give the IOTA-VTI device the power on time of about 15 minutes to update the almanac data before the event recording has to start.

One another detail which is remarkable in the measurement image above. The lit LED numbered with 534 does not show stripes like the other do and so looks more brightful. The answer is given if we take a look on this video image with both fields separated as shown below.

The same video image split in both fields

Both fields of CCIR video image with IOTA-VTI video time insertion

Now both field exposure times are clear visible. The first field #25812 was exposured from 08.514 - 08.534 and the second field #25813 from 08.534 - 08.554. And we can see that the lit LED #534 is captured for a short time at the end/start in both fields. So this LED shows no stripes and looks brighter than all other in the frame image above. If we compare the inserted time stamps 08.5336 and 08.5536 with the real exposure times we have to consider that the IOTA-VTI time stamps are inserted for the end of every video field exposure.

So the result of this measurements shows very clear that this IOTA-VTI device is time stamping very accurate and in a manner as described in the device manual. If the inserted times are used as field exposure end times no additional time shift has to be used. One additional note about the internal GPS board GlobalSat EM-406A used in this device. In the last years I have purchased and used a Garmin GPS 18 LVC, the successor model a Garmin 18x LVC and now the new IOTA-VTI with internal GPS board EM-406A. After the first change from 18 LVC to 18x LVC a very high improvement in sensitivity could be observed. And now the newer technology of this GlobalSat EM-406A GPS board shows that again another big step in sensitivity is possible. The IOTA-VTI device with the GPS inside the device case is much more sensitive in comparison to the very good Garmin 18x LVC.

Pages of the EXTA project

Page #1 - Main page with EXTA description

Page #2 - Measurements with analog video camera modul SK1004XC

Page #3 - Measurements with analog video camera WAT-902H2 Ultimate

Page #4 - Measurements with integrating analog video camera WAT-120N

Page #5 - Measurements with Astro CCD camera Atik 314L+

Page #6 - Measurements with IOTA-VTI device (this page)

Page #7 - Measurements with integrating analog video camera MINTRON 12V1C-EX

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