Varian, Inc.

Robert G Rice

James Patrick Finnigan

Andrew W Munsell

A 1/4 wave circuit switch for use in an NMR probe has a housing with a stepped cavity for precisely locating switch components inside. The 1/4 wave circuit switch cooperates with a 1/4 wave tube and is designed to receive either an external capacitor on a capacitor stick for single tune operations or a 1/4 wave center conductor with a threaded tip on a 1/4 wave stick for double tune operations. For single tune operations, the external capacitor comes into contact at one end with a resiliently supported, movable electrical contact and at the other end with a spring clip inside the housing cavity to orient the external capacitor in parallel with the NMR coil. The movable electrical contact is resiliently biased by a pair of crescent washers supported by an insert plug which serves as a positive stop for the travel of the electrical contact. For double tune operations, the threaded tip of the 1/4 wave center conductor simultaneously contacts a pair of threaded contacts provided inside the housing cavity and spaced by an insulating spacer. The simultaneous contact creates a current path which grounds the NMR circuit through the 1/4 wave tube, so that the NMR circuit may resonate at two separate frequencies. The two frequencies can be easily adjusted by employing an extension tube that effectively changes the length of the 1/4 wave tube and grounds the NMR circuit through the 1/4 wave tube to resonate at different frequencies.

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Mountain Veiw, CA, United States of America

Robert G Rice