Programmable instrumentation for high repetition rate experiments providing control in real time and acquisition of a train of pulses

Abstract

An automated, low-cost programmable instrumentation system which solves many of the problems associated with the data acquisition and control of high repetition rate experiments is described. The system can monitor and control experiments on a pulse-by-pulse basis while digitally storing consecutive pulses which occur in the train. The system compares well with manual test equipment and commercial transient diagnostic systems which cannot provide the high-speed control and data acquisition available here. The oscilloscope used to store the train of pulses can digitize at a maximum rate of 100 MHz, and has 32 kbytes of acquisition memory that can be subdivided into a sequence of as many as 250 separate segments. In order to reduce the system software reinitialization time to acquire each successive sequence within the total train, a novel IEEE-488 compatible microprocessor system is used in conjunction with a host personal computer. The microprocessor controls triggering of the experimental equipment based on digitally acquired waveform information. This information is also used to coordinate the reinitialization of the oscilloscope by the host computer. The system can acquire each and every pulse at repetition rates up to 40 Hz. Above this rate, the probability of acquiring a particular pulse in the train falls slightly below unity due to the finite time required to reinitialize the oscilloscope. The maximum synchronously controllable pulse repetition rate of the microprocessor is 20 000 Hz. Minimum performance specifications are provided which are significantly better than other approaches. The system is employed in high-voltage, dielectric breakdown experiments. For the example given, there are 62 segments in the acquired sequence, with a 100-MHz digitizing rate during the 5-μs acquisition time for each segment. The breakdown pulse in the train and as many as 61 pulses preceding it are obtained.