control for UV-sensitive detectors, and the entire lab was kept clean, and entered via an air-shower. Hardware was handled on a clean flow bench. The detectors were mounted in the tank, along with their flight power supplies, on a platform that moves in 3 axes, and were operated by ground support equipment (GSE) outside the tank. Data were viewed and logged via the GSE, and final images were derived later in a separate computer system.

We describe below the different test results and their implications for science use on Astrosat.

Darks and read rates
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In photon-counting operation, the dark current behaviour is a peripheral concern. But for the UVIT detector system, a quasi-integrate mode feature was also developed, in which it is very important to understand the behaviour of the readout dark current At nominal gain, a single detected photon event will utilize the maximum amount of CMOS ADC bit depth without saturating the detector in order to maximize counting and centroiding fidelity. Therefore two photons detected in one place within a single read-frame will saturate the CMOS. This is analogous to pulse pile-up on single channel photometers. At normal high-voltage operating parameters, the frames are read at approximately 