COMPUTER-BASED CONTROLLER AND AVERAGER FOR THE BALLE-FLYGARE SPECTROMETER

A computer-based controller/averager has been built for the Balle-Flygare pulsed nozzle, Fourier transform, microwave spectrometer. We have integrated gas and microwave pulse control, digitizing and averaging, signal processing, and mirror and frequency control into an IBM PC-AT, allowing the computer to coordinate all processes in the spectrometer. Multiple free induction decays (FIDs) are recorded for a single gas pulse without delay between digitizing sequences by continuously clocking the FID's into multiple segments of digitizer memory. The averager fits into one of the AT's expansion slots and has the unique feature of sharing 16 kbyte of static memory with the CPU. This gives the computer immediate access to the current average since it is already in the computer's memory. The averaging is very fast so that the nozzle and vacuum pump remain the limiting factors for the repetition rate. Programming features are described. The spectrometer is now easier and faster to run. The increased speed and multiple FIDs per gas shot improve the signal-to-noise ratio, thus improving the chances of finding weak transitions. It is possible now to make automated searches for new transitions.