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Detector Count Rate Restrictions

The ETC uses the current count rate screening restrictions, which are taken from Section 11.5 of the COS Instrument Handbook. If the observation will exceed any of the count rate restrictions, a warning message will be given in the output page. The count rate restrictions for the detectors are as follows:

COS Count Rate Screening Limits

Detector	Source type ^1	Type of limit	Limiting count rate ^2
FUV	Predictable	Global	15,000 per segment
		Local	40 per resel ^3
	Irregular	Global	6,000 per segment
		Local	40 per resel ^3
NUV	Predictable	Global	30,000 per stripe
		Local	80 per pixel
	Irregular	Global	12,000 per stripe
		Local	80 per pixel

¹"Predictable" means the brightness of the source can be reliably predicted for the time of observation to within 0.5 magnitude.

²Entries are counts per second.

³An FUV resel is 6 pixels wide by 10 high.

Detector Dark Background

The following table lists the dark count rate and read noise characteristics of the COS detectors as measured in ground tests.

Detector background count rates (per second) for COS.

Detector:	FUV XDL	NUV MAMA
Dark rate (counts sec^-1)	0.5 per cm^2 7.2 × 10^-7 per pixel 4.3 × 10^-5 per resel	34 per cm^2 2.1 × 10^-4 per pixel 1.9 × 10^-3 per resel
Read noise	0	0