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Contributed by Clive
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Thursday, 10 November 2005 |
The dark current issue has been repaired. When we turned the camera on today there was signal in all ports. The reference level for the dark current is derived from the video signal and it looks like there was some change in the delay between the video signal and the sample point. We do not know the reason for this! The delay is set by a series of red DIP switchs on the board labeled "CLAMP DELAY". It was set at 40%. We reduced it to 20% as originally specified in the cameras documentation and this allowed us to set the global level adjust pot closer to the middle of its range. We then set all the ports to about 100 counts.
We are going to take some test data and would like Monday to make sure the system is stable. The microscope should be available for use from 11/15/05 onwards, so sign up quickly!
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Last Updated ( Thursday, 10 November 2005 )
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ScratchNG down for engineering work |
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Contributed by Clive
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Thursday, 10 November 2005 |
Yesterday, 11/9/05, the CCD camera on ScratchNG developed a problem with the dark current levels in the 8 output ports and the system will be "down" until this has been resolved. When the camera was turned on the dark current levels in the ports were very different from the nominal 100 counts and the two left most ports, as seen in the image, had zero counts
The dark current level in each port is controlled by a potentiometer and the global level is also set by potentiometer. It was necessary to turn the global level all the way down to allow the pots on the individual channels to come into range and be set to 100 counts. However, the two leftmost channels could not be adjusted into range.
The supply voltages on the CCD board have been checked, the +5V was at +4.87V so we adjusted the power supply up to +5.00V. This did not solve our problem, but it did give us a little more range in the global pot adjustment.
It seems that the dark current offset voltages have changed and we intend to measure these on the board to see if we can identify any failed chips.
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Last Updated ( Thursday, 10 November 2005 )
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