Variable capacitance measuring device
A variable capacitance measuring device can comprise any one or more features in various different embodiments allow a reliable, compact device to be achieved. A capacitor electrode, a gettering housing, and pinch-off connector may be aligned along a common axis may reduce width dimensions without a substantial increase in length. Temperature-induced variations may be reduced by selecting materials that have coefficients of thermal expansion relatively closer to one another. Substantially varying topologies for ceramic-metal interfaces may reduce the likelihood of external contaminants from reaching the evacuated portion of the device. A tube can be used between the capacitor portion and a gettering housing to isolate external forces and getter activation heat from the sensor. The same tube also reduces heat loss from a heated sensor and protects the electronics from overheating. Embodiments also include processes for using and forming the devices.
1. A variable capacitance measuring device comprising:
an electrode assembly having a first coefficient of thermal expansion; and
an insulating material having a second coefficient of thermal expansion, wherein:
the insulating material laterally surrounds the electrode assembly; and
the second coefficient of thermal expansion is within approximately 50% of the first coefficient of thermal expansion.
2. The variable capacitance measuring device of claim 1 , further comprising a capacitor housing bonded to the insulating material, wherein the capacitor housing:
laterally surrounds the insulating material; and
includes a conductive portion that is electrically connected to a diaphragm.
3. The variable capacitance measuring device of claim 2 , wherein:
the conductive portion has a third coefficient of thermal expansion; and
the second coefficient of thermal expansion is within approximately 50% of the first and third coefficients of thermal expansion.
4. The variable capacitance measuring device of claim 1 , further comprising:
an electrode coupled to the electrode assembly;
a conductive portion bonded to the insulating material; and
a diaphragm coupled to the conductive portion,
wherein:
a combination of the electrode, the diaphragm, and a gap between the electrode and the diaphragm is a variable capacitor; and
a distance between the electrode and the diaphragm is in a range of approximately 50-250 microns.
5. The variable capacitance measuring device of claim 4 , further comprising a pinch-off connector, wherein:
the electrode assembly comprises a getter housing; and
the electrode, the getter housing, and the pinch-off connector lie along a common axis.
6. The variable capacitance measuring device of claim 5 , wherein the electrode assembly further comprises a tube that lies between the getter housing and a capacitor portion of the variable capacitance measuring device, wherein:
the getter housing has a getter housing width and is spaced apart from the capacitor portion by the tube; and
the tube has a tube width that is less than the getter housing width.
7. The variable capacitance measuring device of claim 1 , wherein the electrode assembly, comprises an alloy comprising iron and nickel, and the insulating material is selected from a glass-mica composite and a glass-ceramic material.
8. A variable capacitance measuring device of claim 1 , wherein the insulating material is bonded to a lateral surface of the electrode assembly.
9. The variable capacitance measuring device of claim 8 , wherein the electrode assembly passes through the insulating material.
10. The variable capacitance measuring device of claim 1 , wherein the insulating material contacts a lateral surface of the electrode assembly.
11. The variable capacitance measuring device of claim 10 , wherein the electrode assembly passes through the insulating material.
12. A component for a variable capacitance measuring device, wherein the component comprises:
an electrode assembly having a first coefficient of thermal expansion; and
an insulating material having a second coefficient of thermal expansion, wherein:
the insulating material laterally surrounds the electrode assembly; and
the second coefficient of thermal expansion is within approximately 50% of the first coefficient of thermal expansion.
13. The component of claim 12 , wherein the insulating material comprises a glass-ceramic material.
14. The component of claim 13 , further comprising a capacitor housing laterally surrounding the insulating material, wherein the glass-ceramic material contacts the electrode assembly and the capacitor housing.
15. The component of claim 12 , wherein the insulating material comprises a glass-mica material.
16. The component of claim 15 , wherein the insulating material further comprises a glass seal that lies between the electrode assembly and the glass-mica composite.
17. A variable capacitance measuring device comprising:
an electrode assembly; and
an insulating material, wherein:
the insulating material laterally surrounds the electrode assembly; and
the insulating material has a coefficient of thermal expansion that is substantially similar to coefficients of thermal expansion of each material in a capacitor portion of the variable capacitance measuring device.
18. The variable capacitance measuring device of claim 17 , wherein the electrode assembly has a surface with a substantially varying topology.
19. The variable capacitance measuring device of claim 18 wherein the surface is a lateral surface.
20. The variable capacitance measuring device of claim 17 , further comprising a conductive portion with a substantially varying topology.
21. The variable capacitance measuring device of claim 20 , wherein the substantially varying topology is on a lateral surface.
22. The variable capacitance measuring device of claim 17 , wherein the electrode assembly further comprises an electrode and a getter housing.
23. The variable capacitance measuring device of claim 22 , further comprising a pinch-off connector, wherein the electrode, getter housing and pinch-off connector are axially aligned.