Improvement of time measurement with the INO-ICAL resistive plate chambers

There are many sources of position dependent variation of the intrinsic gain of a single gap RPC, e.g. variation of the thickness of the glass electrodes, the buttons and spacers, different composition of the gas mixture due to improper gas flow, leakage etc. One of the dominant components of the time resolution of a large area single gap RPC is this position dependent gain. Also, there is a variation of timing information as a function of the strip multiplicity as well as the lateral position of the trajectory in the RPC strip coordinate. This paper describes the technique of offline time correction to achieve a time resolution better than a ns. This technique is validated using a large cosmic ray dataset collected with a stack of twelve, 1 x 1m(2) RPCs at TIFR. This paper also mentions a few alternate solutions to improve the time resolution during the operational phase of the INO-ICAL experiment. All these solutions are not only valid for INO, but also for any experiment with large RPC detectors.