ao:cic_analysis

Clock Induced Charge Analysis

This recipe from Mike Ireland:

1) Take at least 10 frames with chosen settings, which is a high gain

mode and with shutter closed

(definitely above a gain of 200 electrons, preferably 500 electrons)

2) Compute a median dark and subtract it.

3) Compute a robust standard deviation, e.g.

stdev = 1.48*sqrt(median(data^2))

4) Compute the number of elements above a threshold e.g.

threshold = 3.5*sigma

length(where(data > threshold))/length(data)

5) Finally, there is a correction you could do which is to divide

the final number by:

exp(-threshold / em_gain_in_dn)

[but to do step 5, you need the EM gain. As long as gain is high, this

correction is small]

Further clarification from Mike:

yes by median dark I mean a bias frame. But computed by taking the median of

lots of bias frames.

Threshold should be a single number, equal to 3.5 times the readout noise.

Data is a bias-subtracted data cube. Use one slice or all slices for better

statistics, but definitely not a sum or average.

My analysis procedure:

Each data cube contains 500 images in rapid succession. I only use

the first 30 images of each data cube for analysis. I sum the 30

images and divide by 30 to get the bias frame. I subtract the bias

frame from each of the 30 images. I then cast the entire 512x512x30

data cube into a 1-D vector, use that vector to generate a robust

standard deviation scalar quantity (1.48*sqrt(median(vector^2)) –

finding the median is the most computationally intensive step), troll

the vector for any values that exceed the robust standard deviation by

a factor of 3.5, divide that number by the total length of the 1-D

vector, and divide by the gain correction factor

(exp(-1.0*thresh/gain)).

Two observations:

1) The vertical shift delay makes a difference in the measured CIC. I

don't understand why this would be the case. If one expects this,

wouldn't we need to know the value used by Andor in their literature?

2) The higher the gain, the larger the clock induced charge. To me,

this would imply that I'm not applying the correction factor correctly

– being called a correction factor implies that its application would

compensate for the differences in the gains.

The summary file:

File Temperature Gain Vertical Shift CIC Fraction

… 0000.fits -50.0000 300 3.30000e-06 0.00426411

… 0001.fits -50.0000 300 3.30000e-06 0.00390681

… 0002.fits -80.0000 300 1.70000e-06 0.00133295

… 0003.fits -80.0000 300 9.00000e-07 0.000842734

… 0005.fits -80.0000 300 5.00000e-07 0.000698496

… 0006.fits -80.0000 300 3.00000e-07 0.000715206

… 0007.fits -80.0000 500 3.30000e-06 0.00416787

… 0008.fits -80.0000 500 1.70000e-06 0.00221594

… 0009.fits -80.0000 500 9.00000e-07 0.00149811

… 0010.fits -80.0000 500 5.00000e-07 0.00114543

… 0011.fits -80.0000 500 3.00000e-07 0.00101927

… 0012.fits -80.0000 800 3.30000e-06 0.00643356

… 0013.fits -80.0000 800 1.70000e-06 0.00335487

… 0014.fits -80.0000 800 9.00000e-07 0.00227567

… 0015.fits -80.0000 800 5.00000e-07 0.00174591

… 0016.fits -80.0000 800 3.00000e-07 0.00155108

… 0017.fits -80.0000 100 3.30000e-06 0.000628299

… 0018.fits -80.0000 100 1.70000e-06 0.000518980

Sample FITS header (in case I overlooked something):

SIMPLE = T / file does conform to FITS standard

BITPIX = -32 / number of bits per data pixel

NAXIS = 3 / number of data axes

NAXIS1 = 512 / length of data axis 1

NAXIS2 = 512 / length of data axis 2

NAXIS3 = 500 / length of data axis 3

EXTEND = T / FITS dataset may contain extensions

COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy

COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A…376..359H

HEAD = 'DU897_BV' / Head model

ACQMODE = 'Kinetics' / Acquisition mode

ACT = 0.0246 / Integration cycle time

KCT = 0.0246 / Kinetic cycle time

NUMACC = 1 / Number of integrations

NUMKIN = 500 / Series length

READMODE= 'Image ' / Readout mode

IMGRECT = '1, 512, 512, 1' / Image format

HBIN = 1 / Horizontal binning

VBIN = 1 / Vertical binning

SUBRECT = '1, 512, 512, 1' / Subimage format

DATATYPE= 'Counts ' / Data type

XTYPE = 'Pixel number' / Calibration type

XUNIT = 0 / Calibration units

TRIGGER = 'Internal' / Trigger mode

CALIB = '0,1,0,0 ' / Calibration

DLLVER = '4.21.30006.0' / Software Version

EXPOSURE= 1.0E-05 / Total Exposure Time

TEMP = -50. / Temperature

READTIME= 5.882353E-08 / Pixel readout time

OPERATN = 0 / Type of system

GAIN = 300 / Gain

EMREALGN= 0 / EM Real Gain

VCLKAMP = 0 / Vertical Clock Amplitude

VSHIFT = 3.3E-06 / Vertical Shift Speed

OUTPTAMP= 'Electron Multiplying' / Output Amplifier

PREAMP = 3. / Pre Amplifier Gain

SERNO = 7103 / Serial Number

UNSTTEMP= -999. / Unstabilized Temperature

BLCLAMP = T / Baseline Clamp

PRECAN = 0 / Prescans

FLIPX = 0 / Horizontally Flipped

FLIPY = 0 / Vertically Flipped

CNTCVTMD= 0 / Count Convert Mode

CNTCVT = 1 / Count Convert

DTNWLGTH= 550. / Detection Wavelength

SNTVTY = 5.44053 / Sensitivity

SPSNFLTR= 0 / Spurious Noise Filter Mode

THRSHLD = 0. / Threshold

PCNTENLD= 0 / Photon Counting Enabled

NSETHSLD= 0 / Number of Photon Counting Thresholds

PTNTHLD1= 0. / Photon Counting Threshold 1

PTNTHLD2= 0. / Photon Counting Threshold 2

PTNTHLD3= 0. / Photon Counting Threshold 3

PTNTHLD4= 0. / Photon Counting Threshold 4

AVGFTRMD= 0 / Averaging Filter Mode

AVGFCTR = 1 / Averaging factor

FRMCNT = 1 / Frame Count

USERTXT1= ' ' / User text

USERTXT2= ' ' / User text

USERTXT3= ' ' / User text

USERTXT4= ' ' / User text

DATE = '2012-07-06T01:22:34' / file creation date (YYYY-MM-DDThh:mm:ss)

FRAME = '2012-07-06T01:22:34.000' / Start of Frame Exposure

ESHTMODE= -1 / Electronic Shuttering Mode

END

If anyone wishes to do further reduction, the data can be found in my home

directory ( ~nils/tmp/andor/andor_cic_tests ) on the office side network.

In comparison with the literature included with the camera, we are very close. The CIC number with the camera tests was done at an EM gain of 1000x, 10 MHz horizontal, and 0.5 usec vertical shift. For our tests, we did 300x, 500x, and 800x, 17 MHz horizontal with varying vertical shifts. The relevant entries from above are:

… 0005.fits -80.0000 300 5.00000e-07 0.000698496

… 0010.fits -80.0000 500 5.00000e-07 0.00114543

… 0015.fits -80.0000 800 5.00000e-07 0.00174591

These match well with the value of 0.00108 events per pixel measured by Andor. My conclusion – the camera meets spec.

2012-09-11:

CIC tests using subregions:

All tests done using an EM gain of 1000x, a temperature of -75C, a readout rate of 10MHz, a 0.5 usec vertical shift rate, and a 90×90 region of interest.

Lower left corner of ROI | Preamp gain | CIC |

(1,1) | 3 | 0.00578088 |

(1,1) | 2 | 0.00447576 |

(1,1) | 1 | 0.00284685 |

(211,1) | 3 | 0.00581897 |

(211,1) | 2 | 0.00419993 |

(211,1) | 1 | 0.00273999 |

(211,211) | 3 | 0.00609663 |

(211,211) | 2 | 0.00490706 |

(211,211) | 1 | 0.00275234 |

2012-09-26:

CIC tests on the six cameras delivered 2012-09-24:

201209xx_camera_shipment

ao/cic_analysis.txt · Last modified: 2018/07/07 08:56 by jones

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