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COS Data Handbook v.3
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COS Data Handbook > Appendix B: COS High Voltage > B.1 COS High Voltage History

B.1 COS High Voltage History
The high voltage on the two FUV detector segments has been adjusted numerous times since launch in order to optimize the performance. Table B.1 lists the nominal high voltage values used since COS installation in 2009.
The initial values used were identical to those used during ground testing. After early on-orbit tests showed that the gain of the MCPs was higher than expected on both segments, the voltages were lowered to return the gain to the prelaunch values. As described in Section 1.2.1, exposure to photon events lowered the gain in the spectral region at the original lifetime position, so the voltage was raised on several subsequent occasions as described in Table B.1 to keep the gain high enough to minimize throughput loss. The voltage will be adjusted as needed in the future in order to keep the gain in the spectral region at acceptable levels.
In addition to the nominal voltages listed in the table, other values have been used in a number of calibration activities, so some data files in the archive have nonstandard voltage levels. For updates on the FUV high voltage, users should refer to:
http://www.stsci.edu/hst/cos/performance/high_voltage/.
Table B.1: Lifetime Position and Nominal High Voltage Values (Segment A/B) for the COS FUV Detector
11051
12802
169/1673
2/9/20154
1
A commanded high voltage of 100 means that no data is collected on that segment.
2
In Cycle 17, the 1230 Central Wavelength setting was replaced by 1280.
3
Segment High Voltage in Volts = -(Commanded voltage*15.69+2500)
4
Last Updated 5/6/2015


COS Data Handbook > Appendix B: COS High Voltage > B.1 COS High Voltage History

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