toolkit for testing ccd cameras – one of tools pi of the sky project wilga 2005 1 / 27 toolkit for...
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Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
Wilga 2005
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Toolkit for testing CCD cameras
Janusz Użycki
Faculty of PhysicsWarsaw University of Technology
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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CCD matrix(Charge-Coupled Devices)
CCD sensors are produced in full choiceof resolution and dimenstions. They areaccessible with diameter bigger than half inch.It is very important in professional astronomyapplications. The CCD sensors are low noiseand have high sensivity.
selected resolution: 2048 x 2048 pixels,15 x 15m each
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it worksmain idea of readout
from CCD sensor
charges vs light
making a photoexposure timephotons
empty
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it works
horizontal shift of charges
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it works
vertical shiftof chargesin a queue
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it works
ADCamplifier
video signal
readouthorizontal shift
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it works
p
n SiO2
cross-section
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it works
Inserting a charge into the CCD matrix
p
n
the charge inserting
egde barier
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it works
Potential well
confinement
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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How it works
three phases
clock signals
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How it works
three stagesof chargemovingprocess
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Consequence of usage the CCDWe had to use own Problems
- the CCD matrix
- control circuits- video signal amplifier- analog to digital converter (ADC)
- noise, temperature of an environment, dark current, ‘hot’ pixels, sensivity gradient
- to find the best timmings- noise, gain selection- digitalization effects: offset, non-linearity etc.
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Solutions
- cold environment (about -10C)- noise and infra-red radiation reduction- statistical methods for analizing „black / dark photos” – finding the best parameters
Example:
CCD amplifier ADClight readout
What is a total gain of the circuit?
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Requirements for the toolkit
for testing CCD cameras- designed for PC platform: Windows XP and 2000 systems (main platform for electronics) Linux system possible
It was used ROOT library packageand Microsoft Visual C++.
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Requirements – continuation (1)
- read images in fits
astronomical format which is used by our aparature (there are raw data from the CCD)
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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Requirements – continuation (2)
- eliminate the offset and ‘hot’ pixels
by substraction of two successive images
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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Requirements – continuation (3)
- display pictures the preview allows to find main errors instantly
- cut egdes for analize to find the best useful part of view
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Requirements – continuation (4)- XY histogram
single pixel distribution it allows to find min/max brightness of view
- X and Y profile (sum or average) to find unvisible errors, dark current effect for example
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Requirements – continuation (5)- X and Y profile (projection)
histograms
- divide the image into regions and make single pixel histograms, fit Gauss distribution parameters (mean and sigma values) We can estimate where is a bad region.
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Requirements – continuation (6)
- plot chart in mean and sigma axis to fit gain line and pitch of one (tangens of angle)
Here is an answer for question:What is a total gain of the circuit?electrons / ADU value = pitch of the line
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CCD Toolkitin action
examples of print-screens
main window(management)
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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CCD Toolkit
in action
previewwindow(enlargement)
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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CCD Toolkit
in action
histogramsfor XY& profiles
Toolkit for testing CCD cameras – one of tools „Pi of the Sky” project
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CCD Toolkit
in action
profiles(projections)
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CCD Toolkit
in action
afterdivisioninto regions
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CCD Toolkit
in action
mean
sigm
a
exampleof badgain fittingreason: offset
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Summary
- program is still testing and it will be developing and improving if necessary
- there is a lot of work for tuning the best parameters for our new cameras