Signal conditioning & data acquisition system for neutral beam calorimeter for NBI SST-1

A positive ion neutral injector capable in delivering 5MW (55kV, 90A) ion beam power is being operated for SST-1 neutral beam injection (NBI). SST-1 Neutral beam injection systems has various components on beam line like ion source, neutralizer, deflection magnet, ion dump, beam dump etc. A Thermocouples based diagnostics is being used for Power density distribution, Beam alignment and System protection. Temperature of beam line components rises when beam passes through them. In order to measure the rise in temperature and estimating beam power profile, beam line components are instrumented with thermocouples (TCs). The thermocouples, which are all K (nickel-chromium/nickel-aluminum) type, have their hot junctions on ground so as to respond quickly to temperature changes. Here `the ground' means beam line components, which in turn are connected to the single reference point of the electrical circuit. The beam itself is dumped on these parts so TCs are subject to severe voltage transients up to few hundred volts. We developed a signal conditioning and data acquisition system to measure the voltage developed across the thermocouples due to rise in temperature. This signal conditioning and data acquisition system is capable in truly producing the temperature rise in presence of voltage transients, high voltage switching during breakdowns. Raw signal from each of these thermocouples is first processed in signal condition cards and then acquired on data acquisition system. This paper presents the scheme of signal conditioning system and obtained results in detailed.