Principle and Design of Flame Arrestor Used in Process Transmitter

Today, I will introduce a national invention authorized patent - flame arrester for process transmitter. The patent was filed by Rosemount Corporation and was granted an announcement on August 24, 2016.

Content description

The present invention generally relates to industrial process transmitters for use in industrial process control systems. More particularly, the present invention relates to flame arresters for industrial process transmitters.

Background of the Invention

Process equipment is mostly used to monitor process parameters such as pressure, temperature, flow and level of process fluids used in industrial processes. For example, process transmitters are often used at multiple locations in an industrial manufacturing facility to monitor various process parameters along various production lines. Process transmitters include sensors that generate electrical outputs in response to physical changes in process parameters. Sensors in the transmitter respond to physical changes in the process fluid being monitored.

Industrial process transmitters are commonly used in facilities that have environments where there are multiple gases or chemicals with ignition potential. For example, transmitters are often found in natural gas processing plants or facilities where hydrogen is used. Alternatively, industrial process transmitters can be used to monitor inherently flammable process fluids. To ensure safe operation of the entire facility, ensure that the industrial process transmitter is explosion proof or flameproof to prevent flames from passing through the transmitter.

A conventional arrangement for fire-sealing hydraulic passages, as described in U.S. Patent No. 4,970,898 to Walish et al. and assigned to Rosemount Corporation of Eden Prairie, Minnesota (MN), involves machining A long and narrow cylindrical passage for a transmitter component such as a flange or plug. Flanges or plugs typically consist of stainless steel sheets of a thickness commensurate with the appropriate length required to provide fire protection access. Fireproof passages are usually a function of the passage's length-to-diameter-diameter ratio (L/D) and the passage's perimeter-to-area ratio (P/A). However, a proper L/D ratio typically thickens the thickness of the flange or plug beyond what is normally required for structural purposes. Also, to machine small diameter vias through such thick plates, electrical discharge machining (EDM) is often used. However, the EDM operation produces a slag layer comprising a layer of material that fills the holes, consisting of recast material of the plate. Slag is dirty and difficult to clean. Slag also harbors moisture, which can interfere with the operation of pressure transmitters and hydraulic systems, for example by changing the sensor's dielectric. The EDM process is also expensive relative to conventional machining processes, such as drilling operations. Accordingly, there is a need for improved fire escapes in industrial process transmitters, particularly less expensive, smaller and less expensive fire escapes.

SUMMARY OF THE INVENTION

The present invention relates to transmitters for sensing process variables in process control systems.

Process transmitter includes transmitter housing, sensor, transmitter circuit, channel and flame arrester. The transmitter housing has an interior space. Sensors are disposed within the interior space to detect process variables of the industrial process and generate detection signals. A transmitter circuit is disposed within the interior space and connected to the sensor. A channel communicates with the sensor and extends through the interior space of the transmitter housing. The channel has a first cross-sectional profile. A flame arrester is positioned in this channel. The flame arrester has a second cross-sectional profile different from the first cross-sectional profile. The flame arrester forms a passage in the interior space of the passage having a cross-sectional area that is less than the cross-sectional area of ​​the passage's first cross-sectional profile. The isolation pathway and flame arrester combination of the present invention achieves several advantages over previous flame arresters and fire suppression pathways.

The sensor 30 in the figure comprises a pressure sensor with a flexible sensor element 40 . In one embodiment, the flexible sensor element 40 comprises a capacitive pressure sensor as known in the art. Capacitance-based pressure sensor cells are described, for example, in US Patent No. 6,295,875 to Frick et al., assigned to Rosemount Corporation of Eden Prairie, Minnesota (MN).

In another embodiment, the flexible sensor element 40 comprises a strain gauge sensor known in the art. A strain gauge pressure sensor unit is described, for example, in US Patent No. 5,709,337 to Moser et al., assigned to Rosemount Corporation of Eden Prairie, Minnesota (MN). Flexible sensor element 40 moves in response to atmospheric pressure PA provided to sensor 30 through reference passage 32 . Flexible sensor element 40 also moves in response to process pressure P1 provided to sensor 40 through isolation passage 34 and connection 22 .

The benefit of the present invention is that it is easier and cheaper to manufacture. Conventional machining operations can be used in place of the more expensive EDM methods. A conventionally machined hole provides a cleaner channel, which reduces the amount of dust and loose material trapped in the channel, thereby reducing potential sensor performance issues such as varying fill fluid volumes. The EDM method also provides porous pores that trap moisture and further degrade the fill fluid properties. Furthermore, in addition to increasing the cross-sectional area and perimeter of the fire extinguishing flow path, the length of the flow path provided by the present invention can also be reduced compared to previous designs.

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