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 type1 | Type of limit | Limiting count rate2 |
| FUV | Predictable | Global | 15,000 per segment |
| Local | 40 per resel3 | ||
| Irregular | Global | 6,000 per segment | |
| Local | 40 per resel3 | ||
| NUV | Predictable | Global | 30,000 per stripe |
| Local | 70 per pixel | ||
| Irregular | Global | 12,000 per stripe | |
| Local | 70 per pixel | ||
| Imaging | Global | 170,000 (over entire detector) | |
| Local | 70 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) | 1.5 per cm2 7.2 x 10-7 per pixel 4.3 x 10-5 per resel |
11 per cm2 2.1 x 10-4 per pixel 1.9 x 10-3 per resel |
| Read noise | 0 | 0 |