Method of and apparatus for in-situ measurement of changes in fluid composition by electron spin resonance (ESR) spectrometry

An electron spin resonance spectrometer for in situ measuring of the degradation of operating machinery lubricating fluids, having in combination,

• a miniaturized RF microwave cavity resonator having
• inlet and outlet passages for continually passing a sample of such fluid through the RF microwave cavity resonator during microwave resonating thereof and during the application therethrough of a relatively slowly varying uniform magnetic field;
• wherein resulting magnetic resonance effects changes in the magnetic susceptibility of the sample at a frequency depending on the Zeeman field at the sample,
• means for relatively rapidly modulating said magnetic field, correspondingly to vary the resonant magnetic susceptibility and said magnetic resonant in such fluid sample;
• and
• means for measuring the resulting RF phase modulation or amplitude modulation thereof to derive an electron spin resonance signal that directly senses the molecular changes in the fluid sample resulting from fluid degradation during operation of the machinery.