Process controller enclosure

The enclosure is a NEMA type 4x, which is designed to be used either indoors or outdoors in a nonhazardous location, and which allows some protection from dirt 

The design of any electrical control unit that will operate in a hazardous location must address the issue of safety, and meet your AHJ s regulation requirements for its fabrication and fitness for its operating environment. 

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Valve Positioners The valve positioner, when combined with an appropriate actuator, forms a complete closed-loop valve-position control system. This system makes the valve stem conform to the input signal coming from the process controller in spite of force loads that the actuator may encounter while moving the control valve. Usually, the valve positioner is contained in its own enclosure and is mounted on the control valve. 

How will the enclosure affect the furnace operation process control ... 

The following items affecting furnace operation and process control should be addressed as the enclosure shape is established ... 

Experimental manipulations of whole lakes or of enclosures within lakes has proven a valuable approach to decipher processes controlling ecological and biogeochemical activity in lakes. The large number of small to moderate-sized lakes on the Amazon floodplain offers an excellent opportunity to employ replicated, whole-system manipulations. Of particular importance would be experimental alterations of flooding periodicity and depth, and of nutrients inputs. 

Electronic control enclosures as well as other electrical equipment are best placed at a lower level, and away from gas generating units, process lines and storage containers. This is because hydrogen rises rapidly away from the ground and normally disperses quite quickly. Such placement is, however, not a substitute for appropriate enclosures since a slight breeze or draft can blow a hydrogen emission sideways and/or downwards, even when adequate ventilation has been provided for the gas to escape upwards and not collect. 

After explaining in the preceding chapter the control of processes by means of process control engineering equipment, subsequently safety devices are treated. They should become effective if the process control engineering measures should fail. Since processes take place inside enclosures (vessels, pipework etc.) the objective is to avoid the loss of their integrity (loss of containment, LOC). An important reason for such a loss is a pressure which lies above the failure pressure of the enclosure. This can, for example, result from component failures. Frequently increased pressure is accompanied by increased temperature, which lowers the load limits of materials and hence their failure pressure. Further reasons for a loss of integrity of enclosures are fires and explosions which cause pressure and/or temperature increases. 

Many modern downstream processes involve the use of equipment items that are relatively compact yet possess high process capacity and are capable of remote, even pre-programmed control. Enclosure within Class III type cabinets offers a practical and reliable means of ensuring that such process steps can be carried out without risk of release of potentially hazardous products into the workplace environment. 

Floudas, C.A., 1999, Recent advances in global optimization for process synthesis, design and control enclosure of all solutions. Comput. Chem. Engng., 23, S963-S973. 

Other equipment specifically designed, built or instchemical weapons production facility, as distinct fi-om a facility constructed according to prevailing commercial industry standards such as equipment made of hi nickel alloys or other special corrosion resisfimt material special equqiment for waste control, waste treatment or air filtering special containment enclosures and safety shields non-sfirndm-d laboratory equipment used to toxic chemicdesigned process control p[Pg.162]

Instrumentation, controls, valves and chemical addition points should be located, as much as practicable, outside the process equipment enclosures unless the anticipated radiation level within the enclosure is not signiEcant. 

Options. Traditional control options for overexposure are material substitution, process change, containment, enclosure, isolation, source reduction, ventilation, provide personal protection, change work practices, and improve housekeeping. A simple way of looking at selection of control options is to find the cheapest option that results in the desired amount of exposure reduction. It is not actually that simple, however, because the various options differ in ways other than cost and degree of control. Some of the other factors to consider in selection of control options are operabiUty, rehabiUty, and acceptabihty. 

Operability. Hidden costs may result from changes in the way a process operates as a result of a control. For example, enclosure and isolation may diminish the abiUty of workers to observe the process. Upsets and dismptions resulting from this loss of intelligence are expensive and generate resistance to the use of these controls, no matter how effective. 

The minienvironment approach to contamination control has been increasing in use. A minienvironment is a localized environment created by an enclosure that isolates the product wafer from contamination and people (48). Another approach is using integrated processing, where consecutive processes are linked in a controlled environment (32). Both requite in situ sensors (qv) to measure internal chamber temperatures, background contamination, gas flow rates, pressure changes, and particularly wafer temperature (4). 

One feature of reprocessing plants which poses potential risks of a different nature from those ia a power plant is the need to handle highly radioactive and fissionable material ia Hquid form. This is necessary to carry out the chemical separations process. The Hquid materials and the equipment with which it comes ia contact need to be surrounded by 1.5—1.8-m thick high density concrete shielding and enclosures to protect the workers both from direct radiation exposure and from inhalation of airborne radioisotopes. Rigid controls must also be provided to assure that an iaadvertent criticahty does not occur. 

Process-variable feedback for the controller is achieved by one of two methods. The process variable can (I) be measured and transmitted to the controller by using a separate measurement transmitter with a 0.2-I.0-bar (3-15-psi pneumatic output, or (2) be sensed directly by the controller, which contains the measurement sensor within its enclosure. Controllers with integral sensing elements are available that sense pressure, differential pressure, temperature, and level. Some controller designs have the set point adjustment knob in the controller, making set point adjustment a local and manual operation. Other types receive a set point from a remotely located pneumatic source, such as a manual air set regulator or another controller, to achieve set point adjustment. There are versions of the pneumatic controller that support the useful one-, two-, and three-mode combinations of proportional, integral, and derivative actions. Other options include auto/manual transfer stations, antireset windup circuitry, on/off control, and process-variable and set point indicators. 

This is a location which is not permanently contaminated but is likely to be prone to fire hazards during processing, storage or handling of explosive gases, chemical vapour or volatile liquids, although under careful and controlled conditions. Eor such locations in addition to a flame- or explosion-proof enclosure, type Ex. d, an increased... 

Since it is not practical to manufacture a llameproof enclosure due to its size and bulk and the number of knockouts and openings on the doors for switches, metering, indicators, and pushbuttons (PBs) etc., it is common practice to locate the.se assemblies some distance from the affected area in a separate well-ventilated room. Depending upon the location and intensity ol contamination, it may be permissible to meet the requirement by using a pressurized enclosure by maintaining a positive pressure inside the enclosure similar to that for motors (Section 7.1.3..3). When there arc many switchgear assemblies, the room itself can be pressurized, which is safer and easier. Small enclosures, however, such as a PB station, switch or a switch fuse unit or an individual starter unit etc., which can be easily made of MS plates or cast iron, as discussed in Section 7.13, can be mounted in the hazardous area while the main MCC can be installed in the control room, away from the contaminated area and from where the process can be monitored. 

The vendor shall be responsible for the selection of proper range, pressure rating, materials of construction and electrical enclosure based on process conditions and electrical area classification. All instruments and controls shall be in accordance with Specification ME-0-JN400. 

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