A fast, time averaging data acquisition system for the PC‐AT bus

A data acquisition system designed for magnetic resonance instrumentation is presented. Its performance may be suitable for a broad set of applications where repetitive and noisy signals must be time‐averaged in order to increase the signal‐to‐noise ratio. The system is built from easily available, low cost parts on a standard board for the PC‐AT (16‐bit) bus. 12‐bit data acquisition and 32‐bit time averaging take place in the memory of the PC under control of its CPU. The sustained data rate, including on‐line signal averaging, can be as high as 250 kHz (500 kHz with interlaced data acquisitions). Timing is accomplished by on‐board software programmable hardware timers. The CPU is then free for other tasks during the time, if any, between acquisition scans. Thus on‐line display of the time‐averaged data and their FT spectrum may be performed without impairing the timing accuracy, which is limited by the 10‐MHz board clock to 100 ns. All functions of the interface are controlled by machine‐language routines, callable from within quickbasic programs.