A fast position encoding system for a delay line based gas filled area detector

Delay line based readout electronics for X-ray area detectors used to carry out kinetic measurements with synchrotron radiation is used mostly because of its relative simplicity and low cost. The key element in the system is a fast multichannel real-time encoding time to digital converter (TDC). For fast time-resolved applications the detector is a 200×200 mm multi-wire gas filled chamber, coupled to two delay lines of about 250 ns to encode the position of the X-ray photon interaction in the X and Y cathode planes. The anode plane of the detector delivers a fast prompt signal which is characteristic of the arrival time of the event. Our method of measurement consists of the simultaneous capture of five time components. These are a time stamp of the anode signal and the relative time for the two pairs of cathode signals collected at the end of the delay lines. These cathode signals arrive at times that are directly proportional to the X and Y co-ordinates of the event. Our electronics is designed around the commercially available LRS 4208 CAMAC time measurement unit. This unit is modified in a way to allow the direct connection of a daughter board which consists of two Logic Cell Arrays (LCA) and some external synchronization and control logic. The first LCA collects the values of the real-time digital interpolators (I ns resolution) and the first level of real-time counters (8 ns resolution) coming from the LRS 4208. Furthermore, it adds another level of real-time counters and is responsible for the computation of the X and Y locations, as well as the rejection of double or incomplete events