The X-ray Sky Monitor(XSM) on The Satellite IRS-P3 ----------------------------------------------------------------

• The XSM is a planar position sensitive proportional counter with a pin-hole of 1 cm2 positioned 16 cm above the detection plane. The FOV is 90o X 90o. The detection plane consists of 32 proportional counter cells with a resistive wire (NiCr) as the anode. Position resolution along the wires is achieved by charge division and perpendicular to the wires it is achieved by cell placing (1 cm). It is estimated that for bright sources (100 mCrabs) a source localization accuracy of 0.1 degree can be achieved. The energy range of the detector is 3 to 6 keV. The front end electronics of XSM is mounted at the back side of the detector. It includes command controllable HV DC/DC convertor, 17 charge sensitive amplifiers and an intricate logic circuit. The layout of these electronics cards are carefully designed to accommodate all the circuit in the minimum available space. The logic circuit evaluates the X-ray events and digitizes the outputs from the two ends of the anodes such that the charge division can be done digitally. The onboard processor controls the detector, accepts the digitized data for each X-ray event and calculates position and arranges the data in the available 512 kbytes memory. Coarse time resolution (1 minute) count rates; two second count rates for each anodes; pixel matrices etc. constitute the onboard data.