scheme is based on a Nearest Neighbour Non-collinear Triplets trigger criterion. Apart from generating the prompt trigger with a coincidence gate width of $\approx$18ns, the trigger generator has a provision for producing a chance coincidence output based on $^{12}$$C_{2}$ combinations from various groups of closely spaced 12 channels. The data acquisition and control system of the telescope is designed around a network of PCs running the QNX (version 4.25) real-time operating system. The triggered events are digitized by CAMAC based 12-bit charge to digital converters (CDC), which have a full scale range of 600 pC. The relative gain of the photomultiplier tubes is monitored regularly once in 15 minutes by flashing a blue LED, placed at a distance of about 1.5m from the camera. Other details regarding hardware and software features of the data acquisition and control system of the telescope are discussed in [@TDAS].

Major upgrade, involving replacement of signal and high voltage cables and installation of new Compound Parabolic Concentrators (CPC) was taken up in November-December 2011 for improving the sensitivity of the telescope. While detailed simulation and experimental results on the Crab Nebula, after upgrade will be presented elsewhere, we present here only a brief summary of 