Process control and

Chemical Gas Detection. Spectral identification of gases in industrial processing and atmospheric contamination is becoming an important tool for process control and monitoring of air quaUty. The present optical method uses the ftir (Fourier transform infrared) interference spectrometer having high resolution (<1 cm ) capabiUty and excellent sensitivity (few ppb) with the use of cooled MCT (mercury—cadmium—teUuride) (2) detectors. 

Apart from the cleanout procedure, the analytical work performed during the production of a bulk pharmaceutical in a three-step synthesis includes 15 different analyses having deterrnination of 22 parameters for raw materials 15 different analyses having deterrnination of 17 parameters in process controls and 11 different analyses having deterrnination of 19 parameters for the product. 

Fiber-Optic Probes. Fiber-optic probes provide remote sampling capabilities to Raman instmmentation, are stable, and give reproducible signals. Their historical niche has been in environmental monitoring. More recently these probes have been used in chemical process control and related areas such as incoming materials inspection. 

A. G. Goossens, M. Dente, and E. Ranzi, Process Control and Optimi tion Handbook, p. 30. 

Historical DataBase Subsystem We have discussed the use of on-hne databases. An historical database is built similar to an on-line database. Unlike their on-line counterparts, the information stored in a historical database is not normally accessed directly by other subsystems for process control and monitoring. Periodic reports and longterm trends are generated based on the archived data. The reports are often used for long-term planning and system performance evaluations such as statistical process (quality) control. The trends may be used to detect process drifts or to compare process variations at different times. 

More microprocessor-based process equipment, such as smart instruments and single-loop controllers, with digital communications capability are now becoming available and are used extensively in process plants. A fieldbus, which is a low-cost protocol, is necessary to perform efficient communication between the DCS and these devices. So-called mini-MAP architec ture was developed to satisfy process control and instrumentation requirements while incorporating existing ISA standards. It is intended to improve access time while... 

The process controller is the master of the process-control system. It accepts a set point and other inputs and generates an output or outputs that it computes from a rule or set of rules that are part of its internal configuration. The controller output seiwes as an input to another controller or, more often, as an input to a final control element. The final control element is the device that affects the flow in the piping system of the process. The final control element seiwes as an interface between the process controller and the process. Control valves and adjustable speed pumps are the principal types discussed. 

Currently, the trend in process control is away from centrahzed process control and toward an increased number of small distributed-control or PLC systems. This trend will put emphasis on the evolution of the fieldbus controller and continued growth of the PC-based controller. Also, as hardware and software improves, the functionality of the controller will increase, and the supporting hardware will be physically smaller. Hence, the traditional lines between the DCS and the PLC will become less distinct as systems will be capable of supporting either function set. 

Transducers The ciirrent-to-pressiire transducer (I/P transducer) is a conversion interface that accepts a standard 4-20 rnA input current from the process controller and converts it to a pneumatic output in a standard pneumatic pressure range (normally (),2-L0 bar [3-15 psig] or, less frequently, 0,4-2,0 bar [6-30 p.sig]). The output pressure generated by the transducer is connected directly to the pressure connection on a spring-opposed diaphragm actuator or to the input of a pneumatic valve positioner. 

The difference in the nature of process controls and safety interlock systems leads to the conclusion that these two should be physically separated (see Fig. 8-89). That is, safety interlocks should not be piggy-backed onto a process-control system. Instead, the safety interlocks should be provided by equipment, either hard-wired or programmable, that is dedicated to the safety functions. As the process controls become more complex, faults are more likely. Separation means that faults within the process controls have no consequences in the safety interlock system. 

Polarization probe.s. Polarization methods other than LPR are also of use in process control and corrosion analysis, but only a few systems are offered commercially. These systems use such polarization techniques as galvanodynamic or potentiodynamic, potentiostatic or galvanostatic, potentiostaircase or galvanostaircase, or cyclic polarization methods. Some systems involving these techniques are, in fact, used regularly in processing plants. These methods are used in situ or... 

The fact that batch processes are not carried out at steady state conditions imposes broad demands on the control system. The instrumentation and control system have to be selected to provide adequate control for a wide variety of operating conditions and a wide variety of processes. In addition, basic process control and shutdown systems have to deal with sequencing issues. This chapter presents issues and concerns related to safety of instrumentation and control in batch reaction systems, and provides potential solutions. 

This control activity includes process control and unit management. Process control includes those loops and devices that perform sequential control, regulatory control, and discrete control. Unit management is responsible for coordinating the activities associated with the batch units (e.g., allocating resources within the unit, ensuring that batch sequences proceed in the proper order, etc.). 

EMEC 1974. Chemical Process Control and Control Rooms. Eoss Prevention Data Sheet No.7-45. Eactory Mutual Engineering Corporation, Norwood, MA. 

Repetitive, irregular or non-symmetrical features require greater process control and complex set-up or tooling requirements. This can be an added source of variability. 

Process control and safety shutdowns must be provided during all modes of operation, not only in the RUN mode. Other modes will require a BPCS configured for the mode operating algorithm and very likely a different set of safety interlocks must provide appropriate protection. Hardwire devices, like timers or software logic, can be used to actuate the SIS pertinent to the operating mode. 

Emission measurements are required for many purposes. They can be used as the basis for emission and air quality studies, as well as for process control and specific technologies to reduce emissions. The reliability of the measured values is constantly improving with developments in monitoring techniques. 

This clause requires the designation of special characteristics that should have been accomplished during product realization (as required by clause 4.2.4.7). As for the documentation of special characteristics, the symbols should have been applied both when establishing the process controls and preparing the control plan (also clause 4.2.4.7) and associated documentation during the planning phase. Therefore the requirements not previously addressed are for the control of special characteristics and evidence of compliance i.e. quality records. 

The object of a process control system is to make economic and sound decisions about the actions affecting the process. Data concerning the variations in process performance are collected and analyzed and decisions taken as to whether action on the process is or is not necessary to maintain production of conforming product (see Figure 9.1). However, process control and process capability are not one and the same, as illustrated in Figure 9.5. 

They mainly apply to products as most of them are concerned with protecting the product from damage and deterioration. They apply to the end product and any items that either form part of the product or are used to produce the product, including any tools, test equipment, and processing materials. Although it is possible for some types of services to deteriorate, this use of the term preservation is covered by the process control and auditing requirements. The only requirements that do apply to services are those for identification, unless product is used in the delivery of a service. If the servicing is done to a product, whether or not the product is owned by the supplier, protection of that product is important. 

If a spillage about once in five years (or however often we think the operator will fail) cannot be accepted, then it is necessary to have two protective devices, one trip (or alarm) to act as a process controller and another to take over when the controller fails. It is unrealistic to expect an operator to watch a level when a trip (or alarm) is provided (see Section 14.7 a). 

However, it did not work out like this. The operator decided to rely on the trip and stopped watching the level. The manager and foreman knew this but were pleased that the operator s time was being utilized better. A simple trip fails about once every two years so the tank was bound to overflow after a year or two. The trip was being used as a process controller and not as an emergency instrument. 

Install two trips, one to act as a process controller and the other to take over if the first one fails. 

Process validation is the procedure that allows one to establish the critical operating parameters of a manufacturing process. Hence, the constraints imposed by the FDA as part of process control and validation of an SMB process. The total industrial SMB system, as described, is a continuous closed-loop chromatographic process, from the chromatographic to recycling unit and, with the use of numerical simulation software allows the pharmaceutical manufacturer rapidly to design and develop worst-case studies. 

Just as in offices, energy efficiency improvements in manufacturing can generate increases in overall productivity far in excess of the gains in output per unit energy. This occurs in two principal ways improved process control and systemic process redesign. 

Better process control and stability because the plenum covers 60% of the bundle fece area, reducing the effects of sun, rain, and hail. 

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