Device for precise centering of an NMR sample tube
A device for centering an elongated sample tube ( 8 ), filled with a measuring substance, relative to a vertical axis of a nuclear magnetic resonance (NMR) receiver coil system ( 9 ) which is rigidly mounted in a support device is characterized in that at least two centering means are provided which are mutually separated in an axial direction of the receiver coil axis and act exclusively in a radial direction on the sample tube ( 8 ), one of which is disposed in the upper region ( 9 a ) and the other in the lower region ( 9 b , 9 b ′) of the NMR receiver coil system ( 9 a-k ) and with at least one positioning means acting on the sample tube ( 8 ) in an exclusively axial direction which may be located either below ( 20 a ) or above ( 17 ) the NMR receiver coil system, wherein the exclusively radially acting centering means ( 9 a , 9 b , 9 b ′) are components of the NMR receiver coil system ( 9 a-k ). The centering accuracy can be increased compared to known devices to obtain optimum results even for sample tubes in the form of measuring capillaries which pose the highest requirements with respect to centering accuracy.
1. A device for centering an elongated sample tube, filled with a measuring substance, relative to a vertical axis of a nuclear magnetic resonance (NMR) receiver coil system which is rigidly mounted in a support device, the centering device comprising:
at least one positioning means, said positioning means acting on the sample tube exclusively in an axial direction, said positioning means disposed either above or below the NMR receiver coil system;
a first centering means disposed in an upper region of the NMR receiver coil system, said first centering means acting exclusively in a radial direction on the sample tube; and
a second centering means disposed in a lower region of the NMR receiver coil system, said second centering means acting exclusively in a radial direction on the sample tube, said second centering means separated in an axial direction of the vertical receiver coil axis from said first centering means, wherein said first and said second centering means each comprise active electrical components of the NMR receiver coil system.
2. The device of claim 1 , wherein said positioning means which exclusively acts on the sample tube in an axial direction is disposed below the NMR receiver coil system and comprises a stop part on which the sample tube is supported in an operating position.
3. The device of claim 1 , wherein said positioning means which exclusively acts on the sample tube in an axial direction is disposed above the NMR receiver coil system and comprises a mounting sleeve which is disposed in a non-slipping manner radially about the sample tube in a collar-like fashion and which is flatly supported at a horizontal terminating surface of a horizontal stop surface disposed above the NMR receiver coil system in an operating position.
4. The device of claim 3 , wherein said stop surface for said mounting sleeve is provided in a floor region on an inside of a rotor which is part of an air turbine for positioning and/or rotating the sample tube, the rotor having a central axial inner bore with a diameter which is larger than an outer diameter of said mounting sleeve.
5. The device of claim 3 , wherein said mounting sleeve is rigidly connected to the sample tube.
6. The device of claim 5 , wherein said mounting sleeve is glued to the sample tube.
7. The device of claim 5 , wherein said mounting sleeve is welded to the sample tube.
8. The device of claim 1 , wherein said first and said second centering means which act exclusively in a radial direction on the sample tube and which simultaneously belong to the NMR receiver coil system, are designed such that an electrically conducting disc of said first centering means is electrically connected to an upper portion of conductor parts of the NMR receiver coil system oriented in an axial direction of a receiver coil axis, wherein two electrically conducting semi-discs of said second centering means are electrically connected to a lower portion of the conductor parts of the NMR receiver coil system oriented in the axial direction of the receiver coil axis to thereby form two terminal elements of the NMR receiver coil system.
9. The device of claim 8 , wherein said first and said second centering means are mounted to electrically insulating support bars which are disposed symmetrically around the sample tube.
10. The device of claim 9 , wherein four support bars are provided.
11. The device of claim 9 , wherein the electrically insulating support bars are made from ceramic, glass or quartz material.