Chandra X-Ray Observatory
	(CXC)
Skip to the navigation links
Last modified: 1 March 2016

Continuous Clocking (CC)-mode for ACIS


The ACIS CCDs are usually operated in timed exposure mode. Data are accumulated for a fixed period of time, the frame time (often 3.1 or 3.2 s) before being read out. The read-out process happens quickly, with a row-to-row transfer time of 0.04 ms. This sequence is repeated for each successive frame of data. Conversely, for continuous-clocking mode observations, data are always being read out, but with a row-to-row transfer time of 2.85 ms instead of 0.04 ms. An advantage of continuous-clocking mode is that it yields a much better time resolution. It is also possible to reduce the effects of pileup for bright sources. However, these benefits come at the cost of a loss of one spatial dimension. The location along a column of a CCD where an event occurs is unknown. The CHIPY coordinate does not represent a position, it represents a time.

Further resources:



Last modified: 1 March 2016
Smithsonian Institute Smithsonian Institute

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email:   cxcweb@head.cfa.harvard.edu Smithsonian Institution, Copyright © 1998-2016. All rights reserved.