초록 ▼

Sensors and methods for measuring displacement are disclosed. In one embodiment, among others, a resistive element is configured to receive an alternating voltage between a first electrical terminal and a second electrical terminal, the first and second electrical terminals defining a length of the

Sensors and methods for measuring displacement are disclosed. In one embodiment, among others, a resistive element is configured to receive an alternating voltage between a first electrical terminal and a second electrical terminal, the first and second electrical terminals defining a length of the resistive element. A signal pickup is capacitively coupled to the resistive element and is configured to be moved along the length of the resistive element at a substantially fixed distance from the resistive element and without contact between the resistive element and the signal pickup. A shielded cable, such as a coaxial cable, electrically connected to the signal pickup carries a signal having an amplitude proportional to the position of the signal pickup with respect to the first and second electrical terminals.

대표청구항 ▼

Therefore, at least the following is claimed: 1. A sensor for measuring displacement comprising: a cylindrical resistive element configured to receive an alternating voltage between a first electrical terminal and a second electrical terminal, the first and second electrical terminals defining an a

Therefore, at least the following is claimed: 1. A sensor for measuring displacement comprising: a cylindrical resistive element configured to receive an alternating voltage between a first electrical terminal and a second electrical terminal, the first and second electrical terminals defining an axial length of the resistive element; a signal pickup capacitively coupled to the resistive element, the signal pickup configured to be moved along at least a portion of the axial length of the resistive element at a substantially fixed distance from the resistive element and without contact between the resistive element and the signal pickup; and a shielded wire electrically connected to the signal pickup, the shielded wire configured to carry a signal obtained from the signal pickup, the signal having an amplitude proportional to an axial position of the signal pickup with respect to the first and second electrical terminals. 2. The sensor of claim 1, wherein the resistive element and the signal pickup are spaced at the substantially fixed distance by an insulating layer. 3. The sensor of claim 1, wherein the first terminal is a voltage source and the second terminal is an electrical ground. 4. The sensor of claim 1, wherein the alternating voltage applied between the first and second terminals oscillates at a fixed frequency and amplitude. 5. The sensor of claim 1, wherein the resistive element is in the shape of a hollow tube and the signal pickup is in the shape of a cylinder, the signal pickup configured to move axially along a portion of the inside of the hollow tube shaped resistive element. 6. The sensor of claim 5, wherein the resistive element and the signal pickup are spaced at the substantially fixed distance by an insulator. 7. The sensor of claim 6, wherein the insulator is an axially uniform layer of nonconductive material coating the signal pickup. 8. The sensor of claim 6, wherein the insulator is a nonconductive tube and the resistance element is an axially uniform layer of resistive material coating the nonconductive tube. 9. The sensor of claim 6, wherein the sensor further includes a hollow rod having a first portion located within the hollow tube and attached to the signal pickup, and a second portion extending outside of the hollow tube, the rod configured to move axially with the signal pickup, and wherein a first portion of the shielded wire is positioned inside the first and second portions of the hollow rod, and a second portion of the shielded wire extends outside of the hollow rod. 10. The sensor of claim 9, wherein the rod is electrically conductive and grounded to provide electrostatic shielding to the shielded wire. 11. The sensor of claim 6, wherein the sensor further includes a rod having a first portion located within the hollow tube and attached to, but electrically isolated from the signal pickup, and a second portion extending outside of the hollow tube, the rod configured to move axially with the signal pickup, and wherein a first portion of the shielded wire is positioned inside the hollow tube and is electrically connected to the signal pickup, and a second portion of the shielded wire extends outside of the hollow tube. 12. The sensor of claim 1, wherein the shielded wire is a conducting wire of a coaxial cable, the coaxial cable including an electrically conductive shield and an insulating layer between the electrically conductive shield and the conducting wire. 13. The sensor of claim 12, wherein the electrically conductive shield is connected to an electrical ground. 14. The sensor of claim 1, wherein the signal pickup is configured to move axially along a portion of the outside of the resistive element. 15. The sensor of claim 14, wherein the signal pickup is a displacement collar. 16. The sensor of claim 1, wherein the resistive element comprises a resistive core. 17. The sensor of claim 1, wherein the resistive element comprises a resistive layer of a substantially uniform thickness on an outer surface of the resistive element. 18. A method for measuring displacement comprising: applying an alternating voltage having a substantially fixed amplitude to a first electrical terminal of a tubular resistive element and electrically grounding a second electrical terminal of the tubular resistive element, the first and second electrical terminals defining an axial length of the resistive element; and determining the position of a signal pickup in relation to the axial length of the resistive element based on an amplitude of an output signal obtained from the signal pickup, the signal pickup being capacitively coupled to, and moveable along, at least a portion of the axial length of the resistive element. 19. The method of claim 18, further comprising the step of: measuring the amplitude of the output signal through a flexible electrostatically shielded wire, the wire electrically connected to the signal pickup and electrostatically shielded by a conductive shield forming a layer around, and insulated from, the wire, the conductive shield extending along a length of the wire, the length defined by a first position near the signal pickup and a second position near the signal output. 20. The method of claim 19, further comprising the step of: moving the signal pickup along the portion of the axial length of the resistive element at a substantially fixed distance from the resistive element and without contact between the resistive element and the signal pickup. 21. The method of claim 18, wherein the resistive element has a circular cross-section. 22. A cylinder comprising: a cylinder body forming a cylindrical hollow chamber for receiving a fluidic medium, the body comprising at least a resistive layer of a substantially uniform thickness, the resistive layer having a first and a second electrical terminal for receiving an alternating voltage; a piston fitted to the inside the hollow chamber of the cylinder body and capacitively coupled to the resistive layer, the piston configured to be moved along at least a portion of the longitudinal axis of the cylinder body at a substantially fixed distance from the resistive layer and without contact between the resistive layer and the piston; and a conducting element electrically connected to the piston for carrying a signal obtained from the piston, the signal having an amplitude proportional to a position of the piston with respect to the first and second electrical terminals of the resistive layer. 23. The cylinder of claim 22, further comprising an insulator between the piston and the resistive layer. 24. The cylinder of claim 23, wherein the insulator comprises a non-conductive tube inside the hollow chamber of the cylinder body, and the resistive layer comprises a resistance film deposited on the non-conductive tube. 25. The cylinder of claim 23, wherein the insulator is an insulating layer formed on an outer surface of the piston. 26. The cylinder of claim 23, wherein the cylinder further includes: a hollow rod having a first portion located inside the cylindrical hollow chamber and attached to the piston, and a second portion extending outside of the cylindrical hollow chamber, the hollow rod configured to move axially with the piston, and wherein a first portion of the conducting element is positioned inside the first and second portions of the hollow rod, and a second portion of the conducting element extends outside of the hollow rod. 27. The cylinder of claim 26, wherein the hollow rod further comprises an insulating layer between the conducting element and the hollow rod. 28. The cylinder of claim 26, wherein at least the second portion of the conducting element is shielded by a conductive shield of a coaxial cable. 29. The cylinder of claim 26, wherein both the first and second portions of the conducting element are shielded by a conductive shield of a coaxial cable. 30. A system comprising: a signal pickup capacitively coupled to a resistive rod, the signal pickup moveable along an axial length of the resistive rod, the axial length defined by a first electrical terminal and a second electrical terminal of the resistive rod; a conductive element electrically coupled to the signal pickup for carrying a voltage signal sensed from the signal pickup to a signal output, the signal having an amplitude proportional to an axial position of the signal pickup with respect to the first and second electrical terminals; and a conductive shield forming a layer around, and insulated from, the conductive element, the conductive shield extending along a length of the conductive element, the length defined by a first position near the signal pickup and a second position near the signal output. 31. The system of claim 30, wherein the resistive rod comprises a resistive core. 32. The system of claim 30, wherein the resistive rod comprises a resistive layer of a substantially uniform thickness on an outer surface of the resistive rod. 33. The system of claim 30, wherein the resistive rod has a circular cross-section. 34. The system of claim 30, wherein the signal pickup is a displacement collar. 35. A system comprising: a tubular body forming a tubular hollow chamber for receiving a fluidic medium, the tubular body comprising at least a resistive layer of a substantially uniform thickness, the resistive layer having a first and a second electrical terminal for receiving an alternating voltage; means for capacitively coupling to the resistive layer, the means for capacitively coupling fitted to the inside the hollow chamber of the tubular body, the means for capacitively coupling configured to be moved along at least a portion of the longitudinal axis of the tubular body at a substantially fixed distance from the resistive layer and without contact between the resistive layer and the means for capacitively coupling; and means for carrying a signal obtained from the means for capacitively coupling, the means for carrying the signal electrically connected to the means for capacitively coupling, the signal having an amplitude proportional to a position of the piston with respect to the first and second electrical terminals of the resistive layer. 36. The system of claim 35, further comprising an insulator between the means for capacitively coupling and the resistive layer. 37. The system of claim 36, wherein the insulator comprises a non-conductive tube inside the hollow chamber of the tubular body, and the resistive layer comprises a resistance film deposited on the non-conductive tube. 38. The system of claim 36, wherein the insulator is an insulating layer formed on an outer surface of the means for capacitively coupling. 39. The system of claim 36, further comprising: a hollow rod having a first portion located inside the tubular hollow chamber and attached to the means for capacitively coupling, and a second portion extending outside of the tubular hollow chamber, the hollow rod configured to move axially with the means for capacitively coupling, and wherein a first portion of the means for carrying a signal is positioned inside the first and second portions of the hollow rod, and a second portion of the means for carrying a signal extends outside of the hollow rod. 40. The system of claim 39, wherein the hollow rod further comprises an insulating layer between the means for carrying a signal and the hollow rod.