Patent Description:
Embodiments of the present disclosure relate to pressure transmitters of the type used in industrial process measurement and control systems and, more specifically, to a pressure sensor for use in a pressure transmitter.

Pressure transmitters are used in industrial process control systems to monitor pressures of process fluids using a pressure sensor that provides an output in response to process fluid pressures. The pressure sensor is typically coupled to the process fluid through an isolation arrangement to prevent exposure of the pressure sensor to the process fluid. The isolation arrangement typically includes one or more isolation diaphragms that are each exposed to the process fluid, and one or more isolation fluid lines each containing an isolation fluid to couple the pressure sensor to the isolation diaphragms. One well known type of pressure transmitter is the Model <NUM> transmitter available from Rosemount Inc. of Shakopee, Minn. Pressure transmitters are also shown in <CIT>, for example.

Some pressure transmitters include differential pressure sensors, which detect a difference between two pressures. The pressure difference detected by the differential pressure sensor may be used to determine a flow rate of the process fluid and other parameters, for example.

Differential pressure sensors conventionally include a pair of sensor body cells. The sensor body cells define an interior cavity in which a diaphragm is supported. The diaphragm divides the cavity into two halves, each of which is coupled to a different pressure input relating to the process fluid through one of the isolation fluid lines. A deflection of the diaphragm in response to the pressure difference between the the cavity halves may be detected using capacitor electrodes of the sensor body cells. The detected deflection of the diaphragm is then used to produce a differential pressure output indicating the pressure difference between the cavity halves.

The sensor body cells each include a metal housing and a glass-to-metal seal or glass insulating cell contained within a cavity of the metal housing. The insulating cell operates to provide a seal between the metal housing and a fluid pathway from one of the isolation fluid lines to one of the cavity halves. Additionally, the insulating cell may provide a seal between the metal housing and lead lines that are coupled to the capacitor electrodes. Lastly, the glass provides electrical insulation between the electrodes and the cell body.

The sensor body cells are manufactured through a glassing operation during which glass or ceramic that is used to form the insulating cell is fused within a cavity of the metal housing and allowed to cool. During the cooling phase, the insulating cell is subject to tensile stresses caused by differences in rates of thermal expansion between the insulating cell and the metal housing. These tensile stresses can lead to cracking of the insulating cell and increased manufacturing costs. Document <CIT> describes a pressure transmitter with a pressure sensor, an isolator diaphragm, and a fill tube. Interior passages in the pressure sensor module body are filled with isolator fluid and provide fluid connections. The isolator fluid couples pressure from the first isolator diaphragm assembly to the pressure sensor. A first crimp portion of the fill tube radially narrows into a substantially solid circular cylindrical cross section to form a first primary seal that is resistant to high pressure cycling. Document <CIT> describes pressure sensor, filled with a dielectric fill-fluid, which includes at least three capacitor plates, disposed about a diaphragm.

Embodiments of the present disclosure generally relate to sensor body cells for use in pressure sensors, and differential pressure sensors that include the sensor body cells. In some embodiments, the sensor body cell includes a metal housing and an insulating cell. The metal housing has a first cavity with a first conical inner surface. A portion of the first conical inner surface is concave. The insulating cell includes a first seal portion within the first cavity and forms a seal with the first conical inner surface, wherein the first seal portion includes a first conical outer surface corresponding to the first conical inner surface and having a convex shape when viewed in cross-section along a plane extending through and approximately parallel to a first axis that is approximately concentric with the first conical outer surface.

Some embodiments of the differential pressure sensor include first and second sensor body cells and a diaphragm supported within an interior cavity formed between the first and second sensor body cells. Each of the sensor body cells includes a metal housing and an insulating cell. The metal housing has a first cavity with a first conical inner surface. A portion of the first conical inner surface is concave. The insulating cell includes a first seal portion within the first cavity and forms a seal with the first conical inner surface, wherein the first seal portion of each insulating cell includes a first conical outer surface corresponding to the first conical inner surface and having a convex shape when viewed in cross-section along a plane extending through and approximately parallel to a first axis that is approximately concentric with the first conical outer surface.

The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the Background.

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements that are identified using the same or similar reference characters refer to the same or similar elements. The various embodiments of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

<FIG> is a simplified diagram of an exemplary industrial process measurement or control system <NUM>, in accordance with embodiments of the present disclosure. The system <NUM> may be used in the processing of a material to transform the material from a less valuable state into more valuable and useful products, such as petroleum, chemicals, paper, food, etc. For example, an oil refinery performs industrial processes that can process crude oil into gasoline, fuel oil, and other petrochemicals.

The system <NUM> includes a transmitter <NUM> that utilizes a pressure sensor, which is formed in accordance with embodiments of the present disclosure, to measure or sense a pressure (e.g., differential pressure) relating to a process <NUM>. In some embodiments, the process <NUM> involves a process material, such as a fluid (i.e., liquid or gas), that is contained or transported through a process vessel <NUM>, such as a pipe, a tank, or another process vessel. The transmitter <NUM> may be coupled to the industrial process <NUM> through an adapter <NUM>, a manifold <NUM> and a process interface <NUM>, for example.

The transmitter <NUM> may communicate process information with a computerized control unit <NUM>, which may be remotely located from the transmitter <NUM>, such as in a control room <NUM> for the system <NUM>, as shown in <FIG>. The process information may include, for example, a differential pressure or a related process parameter, such as a flow rate of a fluid flow through the vessel that is based on the differential pressure.

The control unit <NUM> may be communicatively coupled to the transmitter <NUM> over a suitable physical communication link, such as a two-wire control loop <NUM>, or a wireless communication link. Communications between the control unit <NUM> and the transmitter <NUM> may be performed over the control loop <NUM> in accordance with conventional analog and/or digital communication protocols. In some embodiments, the control loop <NUM> includes a <NUM>-<NUM> milliamp control loop, in which a process variable may be represented by a level of a loop current I flowing through the control loop <NUM>. Exemplary digital communication protocols include the modulation of digital signals onto the analog current level of the two-wire control loop <NUM>, such as in accordance with the HART® communication standard. Other purely digital techniques may also be employed including FieldBus and Profibus communication protocols.

The transmitter or transmitter <NUM> may also be configured to communicate wirelessly with the control unit <NUM> using a conventional wireless communication protocol. For example, the transmitter <NUM> may be configured to implement a wireless mesh network protocol, such as WirelessHART® (IEC <NUM>) or ISA <NUM>. 11a (IEC <NUM>), or another wireless communication protocol, such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol.

Power may be supplied to the transmitter <NUM> from any suitable power source. For example, the transmitter <NUM> may be wholly powered by the current I flowing through the control loop <NUM>. One or more power supplies may also be utilized to power the transmitter <NUM>, such as an internal or an external battery. An electrical power generator (e.g., solar panel, a wind power generator, etc.) may also be used to power the transmitter <NUM>, or charge a power supply used by the transmitter <NUM>.

<FIG> is a simplified cross-sectional view of a portion of the transmitter <NUM> and adapter <NUM> of <FIG>, in accordance with embodiments of the present disclosure. The transmitter <NUM> may include a housing <NUM> that encloses and protects electronics of the transmitter <NUM> from environmental conditions including a differential pressure sensor <NUM>. The housing <NUM> includes a base <NUM> that may include one or more process openings <NUM>, such as process openings 124A and 124B. The process openings may be coupled to the process <NUM> through suitable connections, such as through the adapter <NUM> (attached to the base <NUM> in <FIG>), the manifold <NUM>, and/or process interface <NUM>, as shown in <FIG>.

The exemplary transmitter <NUM> may include diaphragms 130A and 130B that are respectively exposed to pressures P1 and P2 of the process <NUM> that are respectively presented to the process openings 124A and 124B, as shown in <FIG>. The diaphragms 130A and 130B flex in response to the pressures P1 and P2. The flexing diaphragms 130A and 130B communicate the sensed pressure to the pressure sensor <NUM> through lines 132A and 132B, which may be filled with an incompressible fluid (e.g., hydraulic fluid).

The differential pressure sensor <NUM> generates one or more output signals (e.g., capacitance signals) in response to the sensed difference between the pressures P1 and P2. The output signals may be delivered to measurement circuitry <NUM> through lead wires 140A and 140B or another suitable connection, and the measurement circuitry <NUM> may be used to process the output signals and produce a differential pressure signal <NUM>. The transmitter <NUM> may communicate the differential pressure measurement indicated by the signal <NUM> to the control unit <NUM> using any suitable technique, such as by adjusting the current I over the two-wire control loop <NUM>, as discussed above with reference to <FIG>.

<FIG> is a simplified side cross-sectional view of a differential pressure sensor <NUM>, in accordance with embodiments of the present disclosure. The sensor <NUM> includes a pair of sensor body cells 144A and 144B, which may be generally referred to as cells <NUM>. Each of the cells <NUM> includes a cup-like metal housing <NUM>, to which ceramic or glass (hereinafter "glass") is fused to form glass-to-metal seals or glass insulating cells <NUM> (hereinafter "insulating cells"), such as insulating cells 150A and 150B.

The cells <NUM> include concave walls <NUM> that define an interior cavity <NUM>. Fluid pathways <NUM> of each sensor body cell <NUM> extend through openings <NUM> of the metal housings <NUM>, and through the cells <NUM> to openings <NUM> in the walls <NUM>, and couple the lines <NUM> to the interior cavity <NUM>, which is also filled with the incompressible fluid. A sensing diaphragm <NUM> divides the cavity <NUM> into two generally equal and opposite cavity halves 154A and 154B. The diaphragm <NUM> deflects in response to the process pressures P1 and P2 that are respectively transferred to the interior cavity halves 154A and 154B through the lines 132A and 132B and the fluid pathways <NUM>. The displacement of the deflected diaphragm <NUM> is proportional to the difference in the pressures P1 and P2.

The position of the diaphragm <NUM> with respect to the walls <NUM> is detected using one or more capacitor electrodes <NUM> of each sensor body cell <NUM> that are attached to the walls <NUM>. The capacitor electrodes <NUM> form electrical capacitors having capacitances which vary in response to displacement or deflection of the diaphragm <NUM> relative to the walls <NUM> due to the applied pressures P1 and P2. The lead wires 140A and 140B extend through openings <NUM> in the metal housings <NUM> and electrically connect the one or more capacitor electrodes <NUM> to the measurement circuitry <NUM>. The measurement circuitry <NUM> can convert the detected capacitances of the electrodes <NUM> into the differential pressure output signal <NUM>, which, for example, may be communicated to the control unit <NUM> (<FIG>) or another computing device.

The insulating cells <NUM> each include a glass seal portion <NUM> within a cavity <NUM> of the metal housing <NUM> that provides a seal between the metal housing <NUM> and the fluid pathways <NUM>, and a seal portion <NUM> within a cavity <NUM> of the metal housing <NUM> that provides a seal between the metal housing <NUM> and the lead wires <NUM> or pathways containing the lead wires <NUM>. The manufacture of the insulating cells <NUM> of the sensor body cells <NUM> involves a glassing operation, during which the cavities <NUM> and <NUM> of each metal housing <NUM> is filled with molten glass (hot phase) and then allowed to cool (cooling phase). Thus, the shape of the cavities <NUM> and <NUM> of the metal housings <NUM> determines a shape of the seal portions <NUM> and <NUM>.

In some embodiments, the seal portion <NUM> includes a conical outer surface <NUM>, which corresponds to a conical inner surface <NUM> of the housing <NUM>, and is approximately concentric to an axis <NUM>. Similarly, embodiments of the seal portion <NUM> include a conical outer surface <NUM>, which corresponds to a conical inner surface <NUM> of the housing <NUM>, and is approximately concentric to an axis <NUM>, as shown in <FIG>. Embodiments of the present disclosure relate to improvements in the shape of the conical surfaces <NUM> and <NUM> of the seal portions <NUM> and <NUM> over conventional sensor body cells.

<FIG> is a simplified side cross-sectional view of a differential pressure sensor <NUM>, in accordance with the prior art. Elements of <FIG> having the same or similar reference as the element shown in <FIG> generally relate to the same or similar element. The differential pressure sensor <NUM> includes a pair of sensor body cells 444A and 444B. The cells <NUM> each have metal housings <NUM> containing glass-to-metal seals or insulating cells 450A and 450B. The insulating cells <NUM> each include a seal portion <NUM> contained in a cavity <NUM> of the housing <NUM>, and a seal portion <NUM> contained in the cavity <NUM>, which operates similarly to the seal portions <NUM> and <NUM> discussed above.

The seal portion <NUM> includes a conical surface <NUM> that corresponds to a surface <NUM> of the housing <NUM> and is approximately concentric to an axis <NUM>, and the seal portion <NUM> includes a conical surface <NUM> that corresponds to a surface <NUM> of the housing <NUM> and is approximately concentric to an axis <NUM>, as shown in <FIG>. The conical surface <NUM> of the seal portion <NUM> is flat, when viewed in a cross-section taken in a plane extending through and parallel to the axis <NUM>, and the conical surface <NUM> of the seal portion <NUM> is flat, when viewed in a cross-section taken in a plane extending through and parallel to the axis <NUM>, as shown in <FIG>. The flat conical surfaces <NUM> and <NUM> can adversely affect the manufacture of the sensor body cells <NUM> and have other disadvantages.

<FIG> are simplified side cross-sectional views of an insulating cell <NUM> of a conventional sensor body cell <NUM> that includes a seal portion <NUM>, which may represent the seal portion <NUM> or the seal portion <NUM> (<FIG>), and the metal housing <NUM> respectively during hot and cooling phases of a glassing operation. Fluid pathways, lead wires, and capacitor electrodes are not shown to simplify the illustration. Additionally, the degree of shape change illustrated between <FIG> is exaggerated to better illustrate cooling phase issues with the cells <NUM> of prior art differential pressure sensors <NUM>.

During the hot phase of the glassing operation, the molten glass seal portion <NUM> conforms to the cavity <NUM> of the metal housing <NUM> in which it is contained, as shown in <FIG>. The cavity <NUM> of the metal housing <NUM> that receives the molten glass has a conical surface <NUM> that is flat when viewed in a cross-section along a plane extending through and parallel an axis <NUM> that is concentric to the conical surface <NUM>, as shown in <FIG>. Thus, the seal portion <NUM> includes a conical surface <NUM> corresponding to the conical surface <NUM> that is flat when viewed in a cross-section along a plane extending through and parallel to the axis <NUM>.

As the metal housing <NUM> and the glass seal portion <NUM> cool, the insulating cell <NUM> bows outward as shown in <FIG> due to the lower thermal expansion of the glass seal portion <NUM> relative to the metal housing <NUM>. This creates stresses within the seal portion <NUM>, which cause the previously flat conical surface <NUM> (<FIG>) to bend inwardly into a concave shape, when viewed in a cross-section along a plane extending through and parallel to the axis <NUM>, as shown in <FIG>. This inward buckling of the conical surface <NUM> can result in large tensile stresses in the seal portion <NUM>, which can lead to cracking of the seal portion <NUM>. Additionally, the buckling of the conical surface <NUM> may cause the seal portion <NUM> to pull away from the walls of the cavity <NUM> of the metal housing <NUM>, which can lead to pressure leaks in the sensor <NUM>.

Thus, conventional cells <NUM> having seal portions <NUM> and <NUM> that include flat conical surfaces <NUM> and <NUM> during the hot phase of the glassing operation can be costly to manufacture due to cracking of the seal portions <NUM> or <NUM> during the cooling phase of the glassing operation.

The sensor body cells <NUM> formed in accordance with embodiments of the present disclosure shown in <FIG> include insulating cells <NUM> that are subjected to reduced tensile stressing during the cooling phase of the glassing operation relative to the insulating cells <NUM> used in conventional sensors <NUM>. In some embodiments, the conical surfaces <NUM> and <NUM> of the seal portions <NUM> and <NUM> of the insulating cell <NUM> have a convex shape when viewed in a cross-section taken along a plane extending through and approximately parallel to the respective axis <NUM> or <NUM>, as shown in <FIG>. The convex conical surfaces <NUM> and <NUM> are formed due to their conformance to corresponding conical inner surfaces <NUM> and <NUM> of the metal housing <NUM> during the hot phase of the glassing operation. The conical inner surfaces <NUM> and <NUM> of the metal housing <NUM> are concave or at least include portions that are concave. The convex outer conical surfaces <NUM> and <NUM> operate to reduce the tensile stresses in seal portions <NUM> and <NUM> of the cell <NUM> during the cooling phase of the glassing operation relative to the conventional cell <NUM>. As a result, the insulating cells <NUM> are less likely to crack during the cooling phase of the glassing operation thereby increasing manufacturing efficiency and reducing manufacturing costs.

This feature of the seal portions <NUM> and <NUM> of the sensor body cell <NUM> is illustrated in <FIG>, which are simplified side cross-sectional views of a sensor body cell <NUM> including an exemplary insulating cell <NUM> having a seal portion <NUM> in accordance with embodiments of the present disclosure respectively during hot and cooling phases of a glassing operation. The seal portion <NUM> includes a convex conical surface <NUM> that is approximately concentric to an axis <NUM>. The seal portion <NUM> may represent the seal portions <NUM> and <NUM> of the cell <NUM> of <FIG>. Thus, the convex conical surface <NUM> may represent the convex conical surfaces <NUM> and <NUM> of the seal portions <NUM> and <NUM> of <FIG>. The fluid pathway <NUM>, lead wires <NUM>, and capacitor electrodes <NUM> are not shown to simplify the illustration. Additionally, the degree of shape change illustrated between <FIG> is exaggerated to better illustrate shape changes of the cell <NUM> during the cooling phase of the glassing operation.

During the hot phase of the glassing operation, the molten seal portion <NUM> conforms to the inner conical surface of the cavity <NUM> of the metal housing <NUM> in which it is contained forming the convex conical surface <NUM>, as shown in <FIG>. As the metal housing <NUM> and the seal portion <NUM> cool, the sensor body cell <NUM> bows outward as shown in <FIG> due the lower thermal expansion of the glass seal portion <NUM> relative to the metal housing <NUM>. This creates stresses within the seal portion <NUM> that cause the convex conical outer surface <NUM> to bow inwardly, as shown in <FIG>. However, the convex conical surface <NUM> does not buckle in the manner of the conventional seal portion <NUM> to become concave, as shown in <FIG>. Instead, the convex conical surface <NUM> maintains its convex shape when viewed in a cross-section along a plane that extends through and approximately parallel to the axis <NUM>, resulting in lower tensile stresses in the seal portion <NUM> relative to those that develop in the conventional seal portions <NUM>, <NUM> and <NUM>. As a result, the likelihood of the seal portion <NUM> cracking during the cooling phase of the glassing operation is reduced.

Additionally, during use of the sensor body cell <NUM> with high line pressures P1 and P2, the tensile stresses in the seal portion <NUM> can essentially be reversed to compressive forces, which are tolerable by the insulating cells <NUM>. Thus, differential pressure sensors <NUM> utilizing sensor body cells <NUM> having insulating cells <NUM> including seal portions <NUM> or <NUM> having the convex conical surfaces <NUM> or <NUM> can provide reduced manufacturing and usage costs over conventional differential pressure sensors <NUM>.

In some embodiments, the convex conical surfaces <NUM> and <NUM> of the seal portions <NUM> and <NUM> may be approximately in the shape of a section of a sphere. Thus, the convex shape of one or both of the conical surfaces <NUM> and <NUM> may be an arc of a circle. For example, the convex shape of the conical surface <NUM> of the seal portion <NUM> may be an arc of a circle having a radius of approximately <NUM> inches, and the convex shape of the conical surface <NUM> of the seal portion <NUM> may be an arc of a circle having a radius of approximately <NUM> inches. Alternatively, the convex shape of one or both of the conical surfaces <NUM> and <NUM> may be a section of a parabola, or another curve.

In addition to the curved surfaces described above, some embodiments of the seal portions <NUM> and/or <NUM> include sections having flat exterior surfaces. For example, in some embodiments, the seal portion <NUM> includes a cylindrical section <NUM> that may be approximately coaxial to the axis <NUM> and includes a flat exterior surface <NUM> when viewed in a cross-section taken along a plane extending through and approximately parallel to the axis <NUM>, as shown in <FIG>. The seal portion <NUM> may also include a cylindrical section <NUM> that extends to the concave wall <NUM>, and has a flat exterior surface <NUM>, such as when viewed in a cross-section taken along a plane extending through and approximately parallel to the axis <NUM>. The surfaces <NUM> and <NUM> may be parallel to the axis <NUM>, as shown in <FIG>.

Likewise, the seal portion <NUM> may include flat surfaces. For example, the seal portion <NUM> may include a cylindrical section <NUM> having a flat exterior surface <NUM> when viewed in a cross-section taken along a plane extending through and approximately parallel to the axis <NUM>, as shown in <FIG>.

Additional embodiments of the present disclosure relate to a differential pressure sensor <NUM> having the pair of sensor body cells 144A and 144B formed in accordance with one or more embodiments described herein, as shown in <FIG>. Accordingly, the differential pressure sensor <NUM> includes insulating cells 150A and 150B each having the seal portion <NUM> and/or the seal portion <NUM> formed in accordance with one or more embodiments described above. Embodiments of the present disclosure also include a field device or transmitter <NUM> that includes the differential pressure sensor <NUM>, and a process control or measurement system <NUM> that includes the field device or transmitter <NUM>.

Claim 1:
A sensor body cell (144A; 144B) for use in a pressure sensor (<NUM>) comprising:
a metal housing (<NUM>) having a first cavity (<NUM>) with a first conical inner surface (<NUM>); and
an insulating cell (150A; 150B) comprising a first glass seal portion (<NUM>) within the first cavity (<NUM>) and forming a seal with the first conical inner surface (<NUM>), wherein the first glass seal portion (<NUM>) includes a first conical outer surface (<NUM>) corresponding to the first conical inner surface (<NUM>);
characterized in that the first conical inner surface (<NUM>) is concave and the first conical outer surface (<NUM>) has a convex shape when viewed in cross-section along a plane extending through and approximately parallel to a first axis (<NUM>) that is approximately concentric with the first conical outer surface (<NUM>).