Patent Application
20080072681
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present invention function to provide a sensor that provides an accurate measurement of a sensed parameter in high temperature environments. In particular, the present invention provides a sensor that detects a value of a physical property from a value in impedance. For example, the sensor may be employed to measure a capacitance value between the sensor and an external object that is representative of clearance between the sensor and the external object in various systems such as a steam turbine, a generator, a turbine engine, a machine having rotating components, and so forth.
Referring now to the drawings,
In the embodiment illustrated in
Further, the sensor assembly 12 includes a transformer 34 coupled to the sensor 32 for amplifying the measured value in impedance to enhance the signal-to-noise ratio of the sensor 32. In addition, the signal processing unit 20 is coupled to the sensor 32 and the transformer 34 for estimating the sensed parameter based upon the measured impedance value. In the illustrated embodiment, the transformer 34 includes at least one ceramic substrate and at least one electrically conductive line disposed on the ceramic substrate to form at least one winding. In one embodiment, the transformer 34 is an axial transformer. In another embodiment, the transformer 34 is a planar transformer.
The electrically conductive lines 48 may be formed of a metal alloy including platinum, or palladium, or gold, or silver, or combinations thereof. In certain embodiments, the electrically conductive lines 48 are applied on the ceramic tube 46 by using a thick film ink through screen-printing, or stencil-printing, or fine line dispensing and then fired at an elevated temperature in a controlled atmosphere. In certain other embodiments, the electrically conductive lines 48 are applied through patterning and deposition techniques such as sputtering or evaporation. In particular examples, the width of the electrically conductive lines 48 is between about 0.075 mm and about 1 mm and the spacing between the electrically conductive lines 48 is between about 0.05 mm and about 5 mm.
For the illustrated embodiment, the transformer 42 includes first and second electrically conductive layers 50 and 52 disposed on an inner surface of the ceramic tube 46. In one exemplary embodiment, the first and second electrically conductive layers 50 and 52 are applied using a thin film ink of an organo-metallic precursor including platinum, or palladium, or gold, or silver, or combinations thereof. The resulting structure is fired. For the illustrated embodiment, the transformer 42 further includes a first insulation layer 54 covering the electrically conductive lines 48 and a third electrically conductive layer 56 disposed on the first insulation layer 54. Exemplary materials for the first and second insulation layers 54 and 56 include alumina, or aluminosilicate, or stabilized-zirconia, or magnesium oxide, or titania, or silicate, or combinations thereof. The first and second insulation layers 54 and 56 may be applied by sol-gel, colloidal suspensions or from polymeric precursors. The resulting structure is fired. Alternately, the first and second insulation layers 54 and 56 may be applied by sputtering or using a vapor deposition method, such as evaporation.
In certain embodiments, the first or second insulation layers 54 and 56 are formed of a glass, or a glass-ceramic such as a borosilicate or alumino-borosilicate glass. In operation, the glass layer may be applied through techniques such as dip-coating, screen printing, thick-film ink dispensing and so forth. Subsequently, the layer is fired at an elevated temperature. Further, the third electrically conductive layer 56 is formed of a metal alloy including platinum, or palladium, or gold, or silver, or combinations thereof. The third electrically conductive layer 56 may be applied by thick-film ink deposition, or thin film ink deposition, or vapor deposition, or combinations thereof.
A second insulation layer 58 is disposed on the third electrically conductive layer 56. In this exemplary embodiment, the first, second and third electrically conductive layers 50, 52 and 56 comprise metallization layers. The transformer 42 also includes a first metallic via 60 formed in the ceramic tube 46 for connecting the electrically conductive lines 48 to the first metallization layer 50, a second metallic via 62 formed in the ceramic tube 46 for connecting the electrically conductive lines 48 to the second metallization layer 52 and a third metallic via 64 extending through the first insulation layer 54 for connecting the electrically conductive lines 48 to the third metallization layer 56. In the illustrated embodiment, the first metallization layer 50 is provided to facilitate electrical contact with a signal line of a coaxial cable 66 of the signal processing unit 20 (see
As will be appreciated by one skilled in the art, the material and process parameters for forming the transformer 42 may be selected to ensure that the electrically conductive lines 48 remain continuous after processing and that dimensional tolerances are maintained. Further, dimensions of the transformer 42 may be selected to achieve a desired impedance gain. Instead of the above-described autotransformer configuration in which a single coil 48 is used and tapped at the 60 location to make a transformer, two separate coils can be used for the transformer. In an exemplary embodiment, the transformer 42 is an axial transformer having a number of electrically conductive lines 48 disposed on the ceramic tube 46 to form a first coil having a number of metallic windings and a second coil having a single metallic winding disposed on the insulation layer 54. Further, the first coil is electrically coupled to signal and shield lines of the signal processing unit 20 and the second coil is electrically coupled to signal and shield lines of the sensor 42. Thus, a number of configurations may be envisaged for the sensor assembly 40.
In the illustrated embodiment, a second layer 92 of Dupont™ 951Green Tape™ is laminated on the top of the multi-loop planar coil 90 with holes provided at the first, second and third locations for defining the vias 84, 86 and 88. In this embodiment, the vias 84, 86 and 88 are filled with Dupont™ 6142D Ag Cofireable conductor. Further, the coil 90 is co-fired at a temperature up to about 850° C. In addition, connection terminals (not shown) are provided from vias 84, 86 and 88 to a signal line of the signal processing unit 20 (see
The various aspects of the method described hereinabove have utility in applications where measurements of a sensed parameter in a high temperature environment are desired. In certain embodiments, the sensor assembly described above may be employed for measurements of parameters in temperatures upto about 850° C. For example, the technique described above may be used for measuring the clearance between a rotating component and a stationary component in an aircraft engine. As noted above, the technique provides a sensor that would provide a signal with substantially high signal-to-noise ratio at a remote signal processing unit by amplifying a change in impedance thereby enhancing the sensitivity and accuracy of the sensor.
Although only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
