Miniature mass spectrometry: RF amplitude control system design

This thesis covers the methods used to construct and characterize a custom digital RF amplitude control system. Many types of mass spectrometers exist, but few have been miniaturized as much as the Mini instruments developed at Purdue University. The goal of this research was to improve upon an earlier amplitude control system consisting of analog circuits first implemented in the Mini 11.5 mass spectrometer developed at Purdue University. A custom set of control and data acquisition electronics were developed for testing the digital and analog control systems in a Mini 11.5 mass spectrometer chassis. A MATLAB Simulink simulation was done to aid the design of the digital controller. Software code was created in C, VHDL, and Visual Basic.NET to operate and collect mass spectra. Tests were performed to compare and contrast critical performance attributes. A cost analysis was also performed. Important findings were that the digital controller as designed was a more costly solution by a factor of 4, but created a more linear amplification than the previous Mini 11.5 analog solution. The improved linearity increased mass resolution by 0.5. Mass drift measurements showed that the RF signal from the digital controller varied between +0.6 to -.2 m/z, but the analog solution varied between +1.7 to -0.5 m/z