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A maintainer uses calibration modes to determine the various operating parameters of the CCDs. Over time, radiation damage to the CCDs change their respective properties. The calibration modes provide a means to monitor and evaluate these changes.
To perform calibration measurements, a maintainer configures and executes one of the existing science modes described in this document. The ground uses the standard telemetered science data to determine the desired calibration information.
A maintainer measures the Charge Transfer Efficiency by exposing the ACIS detectors to the on-board calibration source, and collects and telemeters events using Timed Exposure Mode's Faint Event Telemetry formats (see Section 3.2.2.3.21 on page 72). The maintainer then determines the Charge Transfer Efficiency using ground-based data analysis.
Other techniques are possible if we implement an event amplitude histogram processing feature for Timed Exposure Science Mode (see Appendix E.2).
A maintainer measures a CCD's Dark Current by comparing CCD output levels (above the overclock level) for Timed Exposure clocked data using different exposure times, and uses ground-based processing of the different Timed Exposure runs to determine the CCD's Dark Current levels.
A maintainer measures the Spectral Resolution, Energy to Pulse Height Gain, CCD Quantum Efficiency, and Background Event Rates as done for the CCD Charge Transfer Efficiency. Each type of function, however, requires different ground-based data analysis of the telemetered data.
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