Personal Computer Controllers

The component controllers used in the controller subsystem portion of the DCS can be of various types and include multiloop controllers, programmable logic controllers, personal computer controllers, singleloop controllers, and fieldbus controllers. The type of elec tronic con-troUer utihzed depends on the size and func tional characteristic of the process apphcation being controlled. See the earlier section on distributed control systems. 

Personal Computer Controller Because of its high performance at low cost and its unexcelled ease of use, apphcation of the personal computer (PC) as a platform for process controllers is growing. When configured to perform scan, control, alarm, and data acquisition (SCADA) functions and combined with a spreadsheet or database management apphcation, the PC controller can be a low-cost, basic alternative to the DCS or PLC. 

The team should have a wide range of knowledge and experience. If a contractor designs the plant, then the HAZOP team should include people from both tlie contractor and client organizations. On a computer-controlled batch plant, the software engineer should be a member of the HAZOP team, which should include at least one other person who understands the computer logic. 

The instrumentation for voltammetry is relatively simple. With the advent of analog operational amplifiers, personal computers, and inexpensive data acquisition-control system, many computer-controlled electrochemical systems are commercially available or custom made. Programming complex excitation waveforms and fast data acquisition have become a matter of software writing. 

Electronic Records and Electronic Signatures Considerations ERES compliance testing for computerized (personal-computer-controlled) instruments is required to demonstrate the functional requirements in the following three key areas [12-14] ... 

Data backup and restore Active data are periodically copied from the hard drive or the personal computer controlling the instrument to a suitable medium such as CD-ROM or DVD or to a separate location such as a controlled file server. 

Business Continuity Planning (Disaster Recovery) A disaster recovery plan should be in place to ensure the continued operation of the laboratory in case of an adverse event that renders the instrument out of commission and hence causes interruption to the business processes which the system supports. Adverse events like the failure of the critical hardware components of the instrument and the failure of the application software do happen in the day-to-day operation of a laboratory. The disaster recovery plan should provide the necessary steps to restore the systems back to a functional state. The steps typically include instructions to reinstall the application software to the personal computer controlling the instrument, to reconfigure the instrument, and to restore the backup data to the instrument. 

The Millilab 1A workstation is a personal computer-controlled automated robotic system which performs sample extraction from filters and SPE devices according to user-defined programs. This was used to compare the efficiency of different SPE materials, as manual error is substantially reduced. The results are listed in Table 26.1. 

An automatic control system consists of various pressure, temperature, and flow sensors, valves and components controlled by a programmable logic controller (PLC), and an operator interface device. The operator interface control device can be as simple as a stop-go for totally dedicated systems, or a personal computer. A personal computer connected to the PLC to provide operator interface, data collection and analysis capability is recommended especially if the system parameter and/or the parts being processed will be changing. More importantly, a computer control system assures consistent and repeatable operation. 

A fully automated, personal computer-controlled spotter (e.g., the Camag Automatic TLC Sampler III), which consists of a stainless steel capillary connected to a dosage syringe operated by a stepper motor, can sequentially apply constant or variable volume samples, chosen from a rack of vials, within the range of 10 nl to 50 pi as spots or bands. 

Automated Computer controlled usually through a personal computer or programmable logic controller. Less frequently by a central control computer or as part of a distributed control system Better repeatability Better process control Lower operating labor costs Data gathering automatic although some analytical instrumentation may remain off line Some to all routine operations may be automated... 

The different types of computer control systems are shown in Fig. 8, while their advantages and disadvantages listed in Table 7. Most new systems are stand-alone systems based on personal computers except for larger research organizations, which may be able to justify the more expensive distributed control systems (see Fig. 9 for a roadmap to selecting a pilot plant control system). 

It is appropriate at this point to indicate our personal motivation for carrying out structural studies, the types of compounds we study, and the experimental conditions we employ. In a very general sense we are interested in the bonding of small molecules and ions, e.g., 02, N2, NO, N2 R+, olefins, and acetylenes, to transition-metal complexes. Because of our interest in bonding, we seek the best solutions we can attain. Rapid, qualitative answers to conformational problems are not our interest. Since those transition-metal systems that bind small molecules generally have the metal in a low oxidation state, and since a low oxidation state is usually stabilized by ligands of the type PR3 (R = alkyl or aryl), solution to our problems involves typically the determination of a large number of structural parameters. With only a few exceptions the intensity data are obtained at room temperature on a Picker FACS-1 computer-controlled diffractometer. Usually the ratio of observations to variables is at least 10, and it is often 20 to 30. 

ENEA (Comitato Nazionale per la Ricerca e per lo Sviluppo dell Energia Nucleare e delle Energie Alternative) in cooperation with CISE (Centro Informazione Studi e Esperienze) developed an advanced automatic corrosimeter for monitoring corrosion in power plants, consisting of two modules the first one acquires data from the probes, and the second one (an IBM personal computer) controls the first module and performs all the required calculations. Several probes can be connected to a single corrosimeter [12]. 

The electrolyte consisted of p.a. chemicals and was deaerated by a nitrogen stream, the temperature being kept at approximately 23°C. Electrochemical results could be stored digitally by using a galvanostat/potentiostat (HEKA Electronics) under computer control, connected by an IEEE interface to a personal computer. The capacity measurements were performed with an impedance workstation (Zahner). All potentials are quoted against the saturated calomel electrode (SCE). 

---