Constructing valve positioners for hazardous areas

A controller for a valve assembly that is configured to meet requirements for use in hazardous areas. These configurations may regulate flow of instrument air to a pneumatic actuator to operate a valve. The controller may comprise enclosures, including a first enclosure and a second enclosure, each having a peripheral wall forming an interior space, and circuitry comprising a barrier circuit disposed in the interior space of one of the enclosures that power limits digital signals that exits that enclosure. In one example, the peripheral wall of enclosures are configured to allow instrument air into the interior space of the first enclosure but to prevent instrument air from the interior space of the second enclosure.

BACKGROUND

Flow controls are important in many industries. Whether found on process lines, distribution networks, or any system that carries flowing material, devices like valve assemblies are vital to regulate material flow within set parameters. Sometimes, these devices must operate in hazardous areas. Valve assemblies, for example, may mount onto process lines that carry flammable or combustible materials, like natural gas. In such cases, it is important that these devices meet certain design specifications to prevent ignition of the material.

SUMMARY

The subject matter disclosed herein relates to improvements that meet these design specifications. Of particular interest are embodiments of control hardware that meets both explosion-proof and intrinsically-safe design standards. This control hardware, or “controller” or “valve positioner,” may integrate onto the flow device to control mechanical mechanisms to regulate this flow. For valve assemblies, these mechanisms may include an actuator, likely pneumatic, that manages movement of a closure member relative to a seat via a stem. During operation, the controller may receive and processes a control signal from a process control system (also “distributed control system” or “DCS system”). The control signal may define operating parameters for the valve assembly. These operating parameters may set an appropriate flow of material through the valve assembly and into the process line. The controller can translate the operating parameters, often in combination with the output from the position sensor, to regulate instrument gas into the actuator. The instrument gas may pressurize (or de-pressurize) the actuator in a way that moves the valve stem and, in turn, locates the closure member in position relative to the seat to coincide with the operating parameters.

Where applicable, like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated. The embodiments disclosed herein may include elements that appear in one or more of the several views or in combinations of the several views. Moreover, methods are exemplary only and may be modified by, for example, reordering, adding, removing, and/or altering the individual stages.

DETAILED DESCRIPTION

The discussion that follows describes embodiments of a controller for use with flow devices and fluid control. The controller is shown to operate with a valve assembly, but the concepts may percolate to other fluid regulating devices (e.g., pressure regulators), particularly those that are for use in hazardous areas. The embodiments have a modular design that separates functional elements into independent, operative modules. Some of these modules may be configured to minimize operating power and temperatures to meet guidelines and requirements typical of “intrinsically-safe designs.” Other modules are built to satisfy explosion-proof standards. When combined, the modules adapt the controller to meet both intrinsically-safe and explosion proof standards and still have appropriate functionality so that the valve assembly can regulate fluids in hazardous areas. Other embodiments are within the scope of the subject matter herein.

FIG. 1depicts a schematic diagram of an exemplary embodiment of a controller100that meets requirements for use in hazardous areas. The controller100is useful to operate a process device, identified generally by the numeral102and discussed herein as a “valve assembly.” In this regard, the valve assembly102may have an actuator104, typically pneumatic, that couples with a valve106via a stem108. The valve106may include one or more valve components (e.g., a closure member110and a seat112). The valve assembly102may integrate into a process line114, often by coupling in-line with a conduit116that carries material118. The valve assembly102may also couple with a process control system120that is configured with a main control loop122that provides one or more signals (e.g., a loop control signal C and a power signal P). The system120may also include a pneumatics supply124that provides instrument air126. As also shown, the controller100may have an architecture that disperses functionality across explosion-proof devices128and intrinsically-safe devices130. The architecture may also include a safety barrier132disposed between the devices128,130. In one implementation, the devices128,130may include a main control device134that manages functions of the controller100. The main control device134couples with one or more peripheral devices (e.g., a first device136, a second device138, and a third device140).

Broadly, the controller100is configured to satisfy requirements for both explosion-proof and intrinsic-safety on a “single” device. These configurations separate operative functions into self-contained devices. Each device has functionality that comports with its respective safety characterization (whether explosion-proof or intrinsically-safe). These features may simplify design as compared to practices to date, often reducing burdens to appropriately arrange, size, and fit components to address both safety standards. The explosion-proof devices128may house power “hungry” functionality (like data processing and diagnostics) because these devices do not limit incoming energy. Further, unlike prior practices, the embodiments separate pneumatic functions from the explosion-proof devices128to the intrinsically-safe devices130. This feature is beneficial because it eliminates “openings” in the explosion-proof devices128that would allow for ingress of pressurized, instrument air, which tends to complicate packaging design decisions in order to meet certifications for explosion protection.

The valve106is configured to regulate flow of material118. Closure member110may embody a plug, a ball, a butterfly valve, and/or like implement that can contact a seat to prevent flow. A sensing mechanism may be useful to monitor the position of the closure member110relative to the seat112. This sensing mechanism can have a position sensor and a mechanical linkage that couples the position sensor with the stem or other structure that moves in concert with the closure member. In some examples, the actuator104includes a pneumatic actuator that converts energy (e.g., compressed instrument air126) into mechanical motion to cause the closure member110to move between an opened position, a partially opened position, and a closed position.

The safety barrier132may be configured to comport with “intrinsically-safe circuit designs.” These configurations may embody circuitry (or circuits) that are effective to power or “energy” limit signals, preferably those signals that enter areas that are not explosion-proof. In one implementation, the circuitry can ensure signals from the main control device134are at low voltages and low currents.

The main control device134may be configured to act as the central “brains” of the controller100. These configurations may have functionality to control or instruct operation of the devices136,138,140. Suitable functions may process signals, including the control signal C, and other inputs to the main control device134. These inputs may correspond with signals that originate from the devices136,138,140, which may also be at the voltage and current levels to meet intrinsically-safe environments. In this regard, the main control device134may be configured for the control signal C to assume any industrial automation protocols. Examples of these protocols include HART, 4-20 milliamp, FOUNDATION Fieldbus, or Profibus. In use, the main control loop122may provide the main control device134with proper control (via the loop control signal C) and power (via the power signal P). In one implementation, power available from the main control loop power122may be approximately 40 milliwatts.

The first peripheral device136may be configured to operate the actuator104. This “pneumatic” configuration may include hardware and software to provide a pneumatic signal to the actuator104. The pneumatic signal may be regulated instrument air126that effectively raises or lowers pressure at the actuator104to manage movement of the closure member110relative to the seat112. Often, the pneumatic signal corresponds with a control signal from the main control device134. This control signal may itself correspond with the loop control signal C, which the control system122uses to set flow of the material118through the valve assembly102.

The second peripheral device138may be configured to allow an end user to interact with the main control device134. This “interactive” configuration includes features to exchange information with the end user. Example features may incorporate display technology to visualize data and information. The features may also include various input devices (e.g., buttons, keyboards, touchscreens, etc.) that can allow the end user to input data, read data, or make selections that influence operation or modes on the controller100.

The third peripheral device140may be configured expand functionality of the controller100. This “options” configuration may provide certain functions that are not essential to the controller100to operate the valve assembly102. Exemplary options may include sensor technology to detect leaks, vibrations, or position of the closure member110. Other options may offer wireless communication technology. End users may select from among several available options to install onto the controller100.

FIG. 2depicts a schematic diagram of an example of the controller100. In this example, the devices134,136,138,140leverage a housing structure that can meet explosion-proof standards. This housing structure uses multiple enclosures142, each having a peripheral wall146that creates an interior space148. A communication interface150may be configured to permit exchange of signals, preferably digital signals (e.g., S1, S2, S3) and power signals (P1, P2, P3). These configurations may include connectors152that may couple with or incorporate into the peripheral wall146, where necessary. Wiring154may extend between connectors152to couple the main control device134with the devices136,138,140. The pneumatic device136may also include a pneumatic fitting156to delivers instrument air126to this device. As also shown, the devices134,136,138,140may include circuitry to enable functions on these devices. On the main control device134, the circuitry may embody barrier circuitry158that operates as the safety barrier140to power limit the outgoing digital signals S1, S2, as desired. The circuitry may also include a control part160and a functional part162across all of the devices134,136,138,140. Bus structure164may be used to exchange digital signals to the connectors152. Examples of the bus structure164may utilize standard or proprietary communication busses including I2C, UART, SPI, UNI/O, 1-Wire, or one or more like serial computer busses known at the time of the present writing or developed hereinafter.

The housing structure allows devices134,136,138,140to couple with one another to form the controller100as a functional, modular “unit.” Often, the enclosure142of the main control device134may operate as a “base” to receive the other, peripheral devices136,138,140. Fasteners like bolts may be useful to ensure safe, secure attachment. When assembled, the pneumatic device136may receive instrument air126directly through pneumatic fittings156. But the peripheral wall146prevents ingress of instrument air126into the interior space148of the main control device134. This feature maintains the interior space148as safe for use with higher-power functions to occur or to house high-power devices.

Enclosures142may be configured to meet relevant operative standards for the respective devices134,136,138,140. For devices136,138, “first” enclosures may satisfy only “intrinsically-safe” designs, where the peripheral wall146may comprise plastic or metals, like sintered metals or formed metal sheets, often at the discretion of the install environment. Some designs may favor materials that are flame-retardant. It is recognized, as well, that the intrinsically-safe “first” enclosures142may not require any external structure at all. On the devices134,140, “second” enclosures may meet “explosion-proof” standards, where the peripheral wall146may comprise cast, machined, or formed metals with appropriate vents and like pressure-dissipating features built therein. Suitable materials may comport with U.L. 1203 standards, where applicable.

The peripheral wall146may adapt to provide ready access to the interior space148. These adaptations may use multi-piece structures that include separable “sections” of the peripheral wall146. The sections can connect together with fasteners (e.g., bolts, screws, etc.) or “quick-release” snaps, clips, or fittings. But care should be taken to ensure appropriate and secure fits that comport with explosion proof standards at least on the explosion-proof devices128.

The communication interface150may facilitate communication across the modular architecture. The devices134,136,138,140may incorporate appropriate computing components (e.g., processor, memory, sensors, etc.) to process and generate the digital signals S1, S2, S3. This feature allows the devices136,138,140to easily swap out of the controller100in lieu of, for example, a replacement device with comparable functionality. Connectors152may include pin-and-socket or like elements to enable this “quick release” capability. In lieu of wiring154, preference may also be given to outfit the controller100with a circuitized substrate (e.g., a printed circuit board) with connections or connectors152and appropriate trace topology. This configuration could allow devices136,138,140to “plug” into the circuitized substrate to transmit signals S1, S2, S3, P1, P2, P3among the devices.

The pneumatic fitting156can permit instrument air126to penetrate the enclosure142of the device136. Quick-release fittings that engage tube or tubing are likely candidates for this design. The pneumatic fitting156resides separate or independent of the explosion-proof enclosures128. This location prevents ingress of pressurized air into the explosion-proof housing of the main control device134(and from the options devices140, as well). As noted above, this feature is beneficial because it reduces cost and complexity of the design of the enclosures142and allows the devices134,140to operate at power levels that are greater than the devices136,138, thus allowing for enhanced or improved functionality.

FIG. 3depicts a schematic diagram of topology166for an example of the barrier circuitry158. Components in the topology166can be arranged to create two zones, e.g., a hazardous zone ZHand a safe zone ZS. The topology166terminates at the connectors152, typically a two-wire interface that “exits” to the hazardous zone ZHwhich for purposes of this example is typically found outside of the explosion-proof housing142of the main control device134. Inside of the safe zone ZS, the topology166may include discrete devices (e.g., a fuse168and a resistor170). A diode device172couples the discrete devices168,170to a ground174. Examples of the diode device172may include one or more zener diodes, but other discrete devices may work as well. In operation, fault voltage across the barrier circuit166will cause current to flow across the diode device172to the ground174. The grounded current causes the fuse170to open, thus limiting current available to the intrinsically-safe devices138,140via connectors152.

FIG. 4depicts a schematic diagram of additional details for circuitry that facilitates functions on the controller100. The control part160may include computing components like a processor176and memory178with data180stored thereon. Data180may comprise executable instructions, like software, firmware, and like computer programs. Processor176may also communicate with driver circuitry182, which operates to interface with other components, for example, bus structure164(e.g., bus, wires, connectors, etc.). As also shown, the control part160may include a power supply184. This device may provide power that energizes the computing components to meet requirements for the controller100to communicate via the automation protocol (e.g., HART, FOUNDATION Fieldbus, etc.). Collectively, the computing components may integrate together as a microcontroller or like solid state device. On the main control device134, the parts160,162may form a main control board that is operative to manage functions, including to provide instructions for operation of the functional part162on other, remote devices136,138,140of the controller100. The functional part162on the pneumatic control device138may be configured to regulate flow of instrument air to the actuator104. This configuration may include a pneumatic control, shown here as a signal converter186that couples with an amplifier188. A sensor190may be useful as well. Examples of the sensor190may measure pressure, temperature, and like parameters. On the interactive device140, the functional part162may be configured to facilitate user interaction with the controller100. It may provide certain peripheral controls (e.g., display192and pushbutton input194), as desired. The options device142may include one or more devices196for different options.

In operation, the controller100may cause the actuator104to move the closure member110to an instructed position. The main control board on the main control device134can process the control signal C to generate an input signal Is, typically electrical current. The pneumatic control device136can use (or process) the input signal Is to stimulate the signal converter186, such as a current-to-pneumatic (I/P) converter, to generate a proportional pneumatic pressure output Ps(also, “signal pressure Ps” or “pilot pressure Ps”). Flow modifying structure on the amplifier188may integrate components (e.g., diaphragms, valves, etc.) into a single or unitary package with, for example, an input for the instrument air126, an input for the signal pressure Ps, and an output port. Collectively, these components may be analogous to pneumatic relays and like devices that, when combined together, can generate, a pneumatic actuator signal Pato operate the actuator104. In one implementation, the structure may leverage one or more diaphragms that move in response to the signal pressure Ps. This diaphragm may operate an internal valve (or valves) to modulate the instrument air126to generate the pneumatic actuator signal Pathat exits the output port. The pneumatic actuator signal Pamay have parameters that are proportional to the signal pressure Psat balanced conditions. Sizing of internal components and flow coefficients (CV) for the flow modifying structure may influence parameters for the pneumatic actuator signal Pa.

The display192may be configured to provide visual representation or indication. These configurations may embody an LCD display, typically alpha-numeric, or like device. This display may present values for the control signal, valve position, or actuator pressure. For touchcreen implementations, the display184may further provide appropriate actuatable inputs, like icons, touch-sensitive buttons, and the like.

The pushbutton input194may operate as the primary local user interface to allow the end user (e.g., a technician) to change settings, readouts, and like operative features. Notably, practice to date may require the user interface to meet “explosion” proof standards, which may require stiffer more robust dials and actuatable member. The input194may offer better, easier actuation because it meets only “intrinsic-safety requirements. This feature may be important for regular maintenance, configuration, and setup, for example, to allow the end user to exit from valve operating mode and step through a menu structure to manually perform functions such as calibration, configuration, and monitoring.

Optional devices196may be configured to expand functionality on the controller100. These configurations may include sensors that can monitor parameters of flow, whether of material118or instrument air132. In some implementations, the sensor may be particularly configured to collect other operating date from the valve assembly102. This operating data may be used in diagnostics that can help schedule preventive maintenance and like tasks. In this regard, the devices196may also include wireless technology, like antenna or receivers/transmitters, so as to property convey the data from the device.

FIG. 5depicts a perspective view of an example of the controller100installed onto exemplary structure200for the valve assembly102. This structure may be useful to regulate process fluids in industrial process lines typical of industries that focus on chemical production, refining production, and resource extraction. As shown, the structure200can include a fluid coupling202that forms a flow path with open ends (e.g., a first open end204and a second open end206). Valve components like the closure member110and seat112may reside inside of the body and hidden in the present view. The structure may also include a pneumatic, diaphragm actuator208with a bulbous housing210, typically with two pieces that clamp about the edges to entrap a diaphragm (not shown) round the periphery. As noted herein, the actuator often turns pressurized instrument air126(FIG. 3) into mechanical motion that causes the closure member110to move relative to the seat112between, for example, an open position, a partially-open position, and a closed position. Although not depicted inFIG. 5, a sensing mechanism may be used to monitor the position of the closure member110. This sensing mechanism can have a position sensor and a mechanical linkage that couples the position sensor with the valve stem108or other structure that moves in concert with the closure member110.

In view of the foregoing, the embodiments offer proper safety measures for use on valve assemblies that operate in hazardous areas. But the concepts here also simplify the design by spreading functionality across differently-configured devices. In this way, the resulting controller may be built to be both intrinsically-safe and explosion-proof, but avoid the cost and time intensive design efforts that are often necessary to meet these standards at the time of this writing.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. An element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. References to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Furthermore, the claims are but some examples that define the patentable scope of the invention. This scope may include and contemplate other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Examples appear below that include certain elements or clauses one or more of which may be combined with other elements and clauses describe embodiments contemplated within the scope and spirit of this disclosure.