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.