Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/external/xmm_sw_cal/icwg/presentations/Time_calibration_KENDZIORRA.pdf Дата изменения: Mon Jun 19 13:59:53 2006 Дата индексирования: Sat Dec 22 15:30:05 2007 Кодировка: Поисковые слова: mars

Pre-launch timing calibration standards

Eckhard Kendziorra IAA TЭbingen


Crab pulse profile measured with EPIC pn


Lessons learned from XMM-Newton
Relative timing of EPIC pn verified pre-launch (but only for relatively short intervals, relative timing verified shortly after launch but second jumps of experiment clock only detected after launch Absolute timing for EPIC pn NOT verified pre-launch (low priority) we still are working on in orbit verification Pre-launch timing calibration/verification essential


Recommendation
- Verify relative timing by long exposures with periodic and stable X-ray beam Errors in relative timing will show up in periodogram and folded light curve - Also verify absolute timing with entire satellite (easy, has been done for ABRIXAS)


What is need for timing calibration
Relative timing - Periodically modulated X-ray beam - directly modulated source (I of X-ray tube) - mechanically chopped beam - chopper wheel - step motor - stable oscillator f/f ~ 10-9 (compare 1 Hz pulse from oscillator with GPS) - monitoring of frequency is essential


Absolute timing - GPS clock with digital interface - Stim ulus LED for low energy detectors X-ray source with mechanical shutter or electrical stimulus

- Trigger stimulus at selected time, compare event time with trigger time
Count rate UTtrig UT


Generation of periodic X-ray signal with chopper wheel

Chopped beam optical sensor

~ 10 cm

Chopper wheel driven by step motor, controlled from stable oscillator f/f ~ 10-9 Stability of rotation must be monitored with e.g. optical sensor or Hall sensor


Chopper for Panter test facility
X-ray detector

Chopper wheel

X-ray beam Optical sensor

Periods from ~ 1ms to 1sec

Chopper wheel for Panter


Light curve time Folded light curve 0 1

2

2

periodogram

P0 Timing okay

Ptrial

P0

Ptrial

Timing NOT okay, phase (time) jump


Absolute time
Generate stimulus at selected time Ttrig Compare measured event time with trigger time T
trig

Ttrig

h

min

sec msec µsec
UT

Comparator T TUT h min

= Ttrig

sec msec µsec

Trigger for stimulus

DCF77 Receiver & Trigger Unit


Jitter of time standards
Terrestrial time standards, DCF77, IRIG: several msec Satellite based systems, GPS, Galileo: < 0.1 µsec use GPS (NOT DCF77, IRIG)


Conclusion
Pre-launch calibration/verification of event timing is - cheap and easy - takes only some days - safes a lot of effort after launch should be part of pre-launch calibration/verification plan for future missions