Abstract
A statistical data processing technique has been implemented by which a significant improvement in accuracy can be achieved when measuring the frequency of noisy sinusoidal signals with an exponential amplitude decay as is the case with free proton precession signals (originating from a proton magnetometer sensor), where the highest accuracy is desired for the shortest observation time. A least square error curve fit method was used and weighing factors were introduced to compensate for the exponential decay of the signal into the noise floor. Additionally, a hardware demodulation process was implemented, enabling a higher quantizing accuracy to be achieved using the same frequency counter clock. Both techniques were realised with appropriate hardware and software and the results confirm the improvement in accuracy.
Highlights
A statistical data processing technique has been implemented by which a significant improvement in accuracy can be achieved when measuring the frequency o f noisy sinusoidal signals with an exponential amplitude decay as is the case with free proton precession signals, where the highest accuracy is desired fo r the shortest observation time
ISSN 0254-3486 = SA T ydskrifvir Natuurwetenskap en Tegnologie 15, no. 4 1996 heid tellerperiodes wat in elke siklus van die sein kan inpas, kan die m eetproses se akkuraatheid verbeter word deur van ’n hoer tellerfrekwensie gebruik te maak relatief tot die frekwensie van die presessiesein
Die wydte van die impulse op die foutwaarskynlikheidsgrafiek lewer ’n goeie maatstaf van die akkuraatheid van metings wat by elke nulkruising verkry kan word en hieruit kan bepaal word wat die weegfaktore vir elke nulkruising tydens die krommepassingsproses moet wees
Summary
Hierdie projek het eerstens ten doel die ondersoek van die rol van weegfaktore by die kleinste-kwadraatfout-metode, sees aangewend vir die bepaling van die frekwensie van ’n protonpresessiesein.'-^Tweedens is ’ndemodulasieproses ingevoerom ’n eenvoudiger en goedkoper meetbaan te verkry wat 'n beter akkuraatheid lewer met relatief minder kompleksiteit. Die sinusvorm ige sein waaruit die frekwensie-inligting onttrek moet word, kan wiskundig sees volg voorgestel word: V(t)=A e '^' sin(27iffi+ n (t). Waar die onbekende frekwensie is wat bepaal moet word en n(t) die ongewensde ruiskomponent is wat as stasionêre Gauss-noubandruis met ’n nulgemiddeld beskou kan word. Vir die eksperimentele ondersoek is ’n 1250 Hz nagebootsde presessiesein met ’n vervaltydkonstante van 0,89 sekondes gebruik. D ie 1250 Hz-sein is verkry deur ’n baie stabiele [9,6] MHz-kristalklok deur 7680 te deel, waarna dit gefilter en vermenigvuldig is met ’n eksponensieel-wegsterwende span ning.
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