WO2013110045A1

WO2013110045A1 - High dielectric strength and dc insulation for pressure sensors and switches

Info

Publication number: WO2013110045A1
Application number: PCT/US2013/022427
Authority: WO
Inventors: Daniel Price; Robert QUZIAK
Original assignee: Hydra Electric Company
Priority date: 2012-01-20
Filing date: 2013-01-21
Publication date: 2013-07-25

Abstract

Disclosed herein is an electronic sensor device includes a sensing module having an interior space configured to measure an environmental property. The device further includes a non-conductive spacer on which the sensing module is seated, the non-conductive spacer including a flange having a thickness dimension for seating the sensing module. A pressure port contains both the sensing module and the non-conductive spacer. A non-conductive sealant adhesive fills a gap between the non-conductive spacer and the sensing module, wherein the gap is determined by the thickness dimension of the flange.

Description

HIGH DIELECTRIC STRENGTH AND DC INSULATION FOR

PRESSURE SENSORS AND SWITCHES

PRIORITY CLAIM

[0001] This application claims priority to and the benefit of U.S. Provisional Patent

Application No. 61/589,184, entitled "HIGH DIELECTRIC STRENGTH AND DC INSULATION FOR PRESSURE SENSORS AND SWITCHES," and filed in the U.S. Patent and Trademark Office on January 20, 2012.

BACKGROUND

Field

[0002] The present disclosure relates to pressure sensors. More particularly, the disclosure relates to methods and apparatus for increasing the dielectric insulation strength of pressure sensors and switches in high voltage electric field environments from direct current (DC) to transient high frequencies.

Background

[0003] Sensors operating in extreme environments, such as sensors used in aerospace applications, may be subject to adverse electrical events. These events may include large transient voltages due to lightning strikes, air flow charge buildup, and electrical system transients. Such high voltage spikes create a differential voltage across the electrical wiring and ground connection points to the sensor. To prevent damage that may be caused by these voltage spikes, a dielectric is typically used to insulate sensitive electronic circuitry.

[0004] The strength of any dielectric determines its ability to protect circuitry on the sensor or other electrical devices from the effects of the voltage spikes. The dielectric strength of most insulators may protect against voltage breakdown from at least 100 volts (V) to as high as 1,000 V, from DC to alternating current (AC) frequencies up to 60 (Hz), with the most common rating being 500 VAC at 60 Hz. However, transient voltage spikes in aerospace applications may range from 5,000 VAC to as high as, or higher than, 15,000 VAC at frequencies up to 1 megahertz (MHz) and higher may occur. Thus, to protect against damage to the internal elements of a sensor unit, an improved dielectric approach capable of withstanding such higher voltage spikes and high frequencies is needed.

SUMMARY

[0005] In one aspect of the disclosed approach, an electronic device includes a sensing module having an interior space configured to measure an environmental property. The device further includes a non-conductive spacer on which the sensing module is seated, the non-conductive spacer including a flange having a thickness dimension for seating the sensing module. A pressure port contains both the sensing module and the non-conductive spacer. A non-conductive sealant adhesive fills a gap between the non-conductive spacer and the sensing module, wherein the thickness dimension of the flange determines the gap.

[0006] In another aspect of the disclosure, a method of insulating an electronic device from high frequency, high voltage, transient impulses includes electrically isolating a sensing module from a pressure port with a non-conductive spacer, and electrically insulating a space between the sensing module and the pressure port with a non-conductive sealant adhesive.

[0007] In yet another aspect of the disclosure, a method of insulating an electronic device from high frequency high voltage, transient impulses includes centering the sensing module concentrically in a cylindrical cavity within the pressure port using a non-conductive retention ring having a central aperture corresponding to a circular dimension of the sensing module.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a perspective cross-sectional view of a pressure sensor adapted to withstand high frequency-high transient voltages that is configured in accordance with one aspect of the disclosure.

[0009] FIG. 2 is a side cross-sectional view of the pressure sensor of FIG. 1.

[0010] FIG. 3 is a magnified view of a portion of the side cross-sectional view of FIG. 2 to provide further detail for the pressure sensor of FIG. 1

[0011] FIG. 4 is a flow diagram illustrating a process for manufacturing the pressure sensor of FIG. 1 in accordance with one aspect of the disclosure.

DETAILED DESCRIPTION

[0012] The detailed descriptions set forth below, in connection with the associated drawings, is intended to provide a disclosure of the various possible configurations of a high dielectric strength and voltage isolation system as implemented in a sensor, and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details.

[0013] Generally, providing increased dielectric strength in sensor devices for voltages ranging from 100 to 1,000 V at 60 Hz AC may be obtained by incorporating dielectric isolation into a sensing mechanism on the sensor devices. In pressure and strain gages, for example, a thick film, non-polar dielectric layer may be deposited on a metal diaphragm, and a thin film sensor is then formed on this dielectric layer. Bonded strain gages may typically be sense resistors formed on an insulating polymer substrate. Silicon micro- electromechanical systems (MEMS) sensors may be micro-machined silicon chips anodically bonded to a glass base. Incorporating the electrical isolation physically between the strain sensing circuit and the flexible membrane it is attached to may place physical and mechanical limitations on the dielectric strength. This coupling requirement limits the thickness of the insulating material that limits, in turn, the resistance to dielectric breakdown.

[0014] In accordance with various aspects of the high dielectric strength and voltage isolation system disclosed herein, a method and apparatus provides for eliminating dielectric insulation from any direct stress path of a sensor while enabling high voltage insulation that is uncoupled from the sensing mechanism. FIGs. 1-3 illustrate various views and portions of a pressure sensor 100 adapted to withstand high frequency and large transient voltages. The sensor 100 includes an independent sensing module 105 that may include a metal flexural diaphragm 110 attached to a sensor support structure 115. Sensing circuitry 120 is formed on an exterior facing surface 112 of the diaphragm 110 to sense flexture of the metal flexural diaphragm 110 resulting from a pressure differential between the exterior facing surface 112 and an interior facing surface 113.

[0015] In one aspect of the disclosure, the sensing module 105 may be seated on a flange

125 of a non-conductive spacer 130. The non-conductive spacer 130 may be made from a high dielectric material, such as Ultem™. The non-conductive spacer 130 may be seated in a pressure port 135, wherein the flange 125 serves to seat the sensing module 105 on a corresponding flat portion 136 of the pressure port 135. Preferably, the sensing module 105, non-conductive spacer 130, and pressure port 135 may be substantially cylindrically symmetric, with fit tolerances selected to be appropriate for each specific industrial application.

[0016] Accordingly, the non-conductive spacer 130 and the pressure port 135 may have an aligned axial spacer through-hole 131 and a pressure port through-hole 137, respectively, to admit gas or fluid to a cavity 111 including an interior facing surface 113 of the diaphragm 110. Pressure transmitted by the admitted gas or fluid applies the force to flex the diaphragm 110, thereby causing the sensing circuitry 120 on the exterior facing surface 112, which reacts to the pressure, to provide a corresponding output signal. [0017] A thickness of the flange 125 determines a dimension of a gap 126 that separates a bottom surface 106 of the sensing module 105 from the flat portion 136 of the pressure port 135. The gap 126 may be filled with a non-conductive sealant 127, such as an adhesive, an epoxy resin, a conforming gasket, or an O-ring, for example, to provide additional dielectric insulation between the pressure port 135 and the sensing module 105 above and beyond the insulation already provided by the non-conductive spacer 130. The non-conductive spacer 130 and flange 125 may be selected of a material and have a dimension so that the spacer 130, flange 125, and non-conductive sealant 127 may provide adequate resistance to high voltage breakdown, up to a specified voltage and transient frequency.

[0018] A non-conductive retention ring 140 is configured with an outside thread 142 that is sized to mate to a corresponding inside thread 144 on an inside cavity wall 146 of the pressure port 135 surrounding the sensing module 105. The non-conductive retention ring further configured to fit around the sensing module 105, and may also be configured to center the sensing module 105 in the pressure port 135 while pressing the sensing module 105 toward the flange 125 of the non-conductive spacer 130, thereby aligning the sensing module 105 coaxially with the pressure port 135 and maintaining the gap 126 to be substantially equal to the thickness of the flange 125.

[0019] Referring to FIGs. 1 - 2, a plurality of access holes 150 may be provided in the non- conductive retention ring 140 so that an appropriate tool, such as a spanner wrench, for example, may be used to screw the non-conductive retention ring 140 the sensing module 105 towards the flange 125. The cavity 147, bounded by the cavity wall 146, provides a space for any extra sealant 127 to be displaced as the non-conductive retention ring 140 is tightened, and further to avoid unintended differential pressure buildup in the inside cavity 147 relative to the exterior facing surface 112. The access holes 150 may also provide pressure equalization between the gap 126, as filled with the sealant 127, and the exterior facing surface 112 of the sensing module 105.

[0020] It may be appreciated that a desired level of high voltage isolation over a wide frequency range of electrical transient impulses may be achieved using a combination of a selection of non-conductive material dielectric properties, coupled with a dimensioning of the spacer 130, retention ring 140, gap 126, and sealant 127. It may be further appreciated that such elements may be applied to protect a variety of electronic devices other than sensor circuits, including switches or other devices that may be employed in environments subject to high voltage static discharge and transient electrical impulses. [0021] For many applications, the gas or fluid admitted through the spacer through-hole 131 and pressure port through-hole 137 are non-conductive and have dielectric properties sufficient to prevent electrical breakdown up to specified transient voltages and frequencies, and pressures up to and greater than 100 psi. Air and uncontaminated hydraulic fluids, for example, may be sufficiently insulating to prevent such breakdown. However, as hydraulic fluid becomes contaminated, the likelihood of dielectric breakdown increases. In that case, various surfaces of the sensing module 105 may be coated with a suitable material, including a surface of the cavity 111 such as the diaphragm interior surface 113 of the sensing module 105, and the bottom surface 106. Such materials may include Sylgard™ 184, 182, 160 and 170 silicone encapsulants, Sylgard™ 527 dielectric gel, a parylene coating, SIFEL™ 827 gel, or an equivalent insulating coating.

[0022] As shown in FIG. 4, a process 400 of manufacturing the pressure sensor 100, the non- conductive spacer 130 may be installed (at 410) in the pressure port 135 with a bottom surface of the flange 125 of the non-conductive spacer 130 seated on the flat 136 of the pressure port 135. The non-conductive sealant 127 may be applied (at 420) to the flat 136, either before or after the non-conductive spacer 130 is installed, where a thickness of the non-conductive sealant 127 is at least as thick as a thickness of the flange 125 in order to fill the gap 126.

[0023] The sensing module 105 may be installed (at 430) to fit concentrically over the non- conductive spacer 130 and be seated on a top surface of the flange 125. An amount of the non-conductive sealant adhesive 127 used is sufficient to fill the gap 126 when the sensing module is installed. The non-conductive retention ring 140 may be installed (at 440) concentrically over the sensing module 105 and may be screwed down via the outside thread 142 and the corresponding inside thread 144 of the cavity wall 146 to impress the flange 109 on the sensing module 105 toward the flange 125 of the non-conductive spacer 130, thereby aligning the sensing module 105 coaxially with the pressure port 135 and controlling the gap 126 to be substantially equal to the thickness of the flange 125.

[0024] It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein. The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to previous or other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more." Unless specifically stated otherwise, the term "some" refers to one or more. A phrase referring to "at least one of a list of items refers to any combination of those items, including single members. As an example, "at least one of: a, b, or c" is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase "means for" or, in the case of a method claim, the element is recited using the phrase "step for."

Claims

CLAIMS WHAT IS CLAIMED IS:

1. An electronic device comprising:

a sensing module comprising an interior space configured to receive at least one of a gas and a fluid;

a non-conductive spacer on which the sensing module is seated, the non-conductive spacer comprising a flange having a thickness dimension for seating the sensing module; a pressure port to contain the sensing module and the non-conductive spacer; and a non-conductive sealant filling a gap between the non-conductive spacer and the sensing module, wherein the gap is determined by the thickness dimension of the flange.

2. The device of claim 1, wherein the non-conductive sealant comprises at least one of an adhesive, an epoxy resin, conforming gasket and an O-ring.

3. The device of claim 1, wherein the sensing module, non-conductive spacer and pressure port are arranged coaxially.

4. The device of claim 1, wherein the non-conductive spacer and the pressure port comprise respective aligned coaxial through holes.

5. The device of claim 1, wherein the interior space is coaxially aligned with the non- conductive spacer through hole.

6. The device of claim 5, wherein the at least one of the gas and fluid is introduced to the interior space via the respective aligned coaxial through holes of the non-conductive spacer and pressure port to be sensed by the sensing module.

7. The device of claim 1, wherein the sensing module comprises:

a sensor support structure;

a fiexural metal diaphragm supported by the sensor support structure; and sensing circuitry formed on the fiexural metal diaphragm, the sensing circuitry being responsive to pressure induced flexure of the metal diaphragm.

8. The device of claim 7, the sensing module further comprising a sensor support flange around a base of the sensor support structure opposite the metal flexural diaphragm.

9. The device of claim 7, the pressure port further comprising:

a cylindrical cavity coaxially surrounding the sensor support structure; and a threaded interior wall of the cylindrical cavity arranged coaxially with the cavity.

10. The device of claim 9, further comprising:

a non-conductive retention ring comprising:

a thread on an exterior edge of the non-conductive retention ring configured to mate with the threaded interior wall of the cylindrical cavity;

a central aperture adapted to fit around the sensing module, and wherein the retention ring is adapted by screw action of the threaded exterior edge of the non-conductive retention ring and the interior threaded wall of the cylindrical cavity to impress the sensing module by force on the sensor support flange toward the flange of the non-conductive spacer.

11. The device of claim 10, wherein the non-conductive spacer, non-conductive sealant adhesive and non-conductive retention ring comprise materials and dimensions to resist transient electrical impulses up to approximately 15,000 V.

12. The device of claim 10, wherein the non-conductive spacer, non-conductive sealant adhesive and non-conductive retention ring comprise materials and dimensions to resist transient electrical impulses from DC to approximately 1 MHz.

13. The device of claim 1, wherein the interior space of the sensing module is coated with an insulating material adapted to resist transient dielectric breakdown up to a specified voltage level and frequency.

14. A method of insulating an electronic sensing device from high frequency high voltage transient impulses comprising:

electrically isolating a sensing module from a pressure port with a non-conductive spacer; and electrically insulating a space between the sensing module and the pressure port with a non-conductive sealant adhesive.

15. The method of claim 14, further comprising centering the sensing module

concentrically in a cylindrical cavity within the pressure port using a non-conductive retention ring having a central aperture corresponding to a circular dimension of the sensing module.

16. The method of claim 15, wherein the sensing module comprises a sensor support structure having a sensor support flange around a base of the sensor support structure opposite the metal flexural diaphragm.

17. The method of claim 16, wherein the non-conducting spacer comprises a flange having a thickness dimension for seating the sensor support flange of the or support structure and seating the non-conducting spacer in the cylindrical cavity within the pressure port.

18. The method of claim 17, wherein an interior wall of the cylindrical cavity has a screw thread, and an edge of the non-conductive retention ring has a corresponding screw thread, the method comprising:

impressing the sensing module toward the flange of the non-conductive spacer by screwing the retention ring into the cylindrical cavity against the base flange.

19. The method of claim 14, further comprising electrically insulating an interior space of the sensing module with an insulating material adapted to resist transient dielectric breakdown up to a specified voltage level and frequency.