Time-shared control

A typical meter site in the Conroe unit was shown in Fig. 8. The three-way, two-position divert valve is the First point in the system where CPC has control. An RTU provides signals to the meter site with an electronic output, which controls the divert valves to direct individual wells to production or test. Since emulsion from both the production and test separators flow through a common NOD, net oil measurement must be kept separate to record total meter site production and individual well production. Separate measurements are accomplished through time-sharing control circuits in the automation control panel. Control signals open and close... 

Sometimes the control loop is opened intentionally. A single contlnu ous analyzer may be used to sample two streams, being alternately a member of each loop. Recently single controllers have been shared among a number of loops, an operation called time shared control. ... 

The distinction between mini - and microcomputers is becoming essentially one of size and price. Minicomputers, which use 16- or 32-bit words, had much larger memories than microcomputers and could be used for the control of several laboratory instruments on a time-sharing basis. However, microcomputers are becoming ever more powerful. Although some still use 8-bit words, 16-bit and 32-and 64-bit word machines are becoming stan-... 

Digital computers are used in process control systems on a time-shared basis. A single digital computer (or microprocessor) services a number of control... 

In the late 1970s, Hewlett-Packard introduced the HP-3300 series data-acquisition system, which was able to connect to 60 chromatographic instruments through an A/D converter. This was the beginning of what would become a revolution in CDS development within the analytical instrument industry. By the mid-1980s, all of the major analytical instrument manufacturers offered network-based data-acquisition systems Beckman, HP, PE, VG, and Waters. These were multi-user, time-sharing systems that used A/D converters to acquire data from the instruments. Instrument control, both HPLC and GC, was a capability that would soon follow. Several CDS manufacturers offered serial control of the HP 5890 GC while Waters also offered instrument control for their own HPLCs. 

In the initial candidate architecture (control structure), a decision is made to introduce a human operator in order to supervise robot movement as so many of the hazards are related to movement. At the same time, it may be impractical for an operator to monitor aU the activities so the first version of the system architecture is to have the TTPS control system in charge of the non-movement activities and to have both the TTPS and the control room operator share control of movement. The safety-guided design process, including STPA, will identify the implications of this decision and wUl assist in analyzing the allocation of tasks to the various components to determine the safety tradeoffs involved. 

Spray pyrolysis polycrystalUne Amorphous to 5-60 pm h" Economical upscaling, time sharing of laser, relatively low deposition rate Robust technology, upscaUng possible, easy control of... 

Control zone This is the area of connectivity to control systems such as controllers (PLCs), human—machine interfaces (HMIs), and basic I/O devices such as actuators and sensors. Basically, there are three sections shown, namely, a management information system for plant management (which at times shares data with the database zone as discussed earlier), a main process control (namely, closed/open loop control system and data monitoring), and an applicable area control (e.g., choke kill control in offshore drilling, or offsite control like a coal handling plant in a power station). All I/Os are connected to this zone either by hardware directly or by a fieldbus system. This zone has very high priority and firewalls like a control firewall may be deployed. Additional external firewalls may also be used. 

In the operation of time-sharing, each controlled variable is sampled, just as if the measurement were discontinuous. Consequently the properties of the sampled loops that have just been examined apply. Figure 4.27 is a skeleton representation of a DDC system. As each variable is scanned, its respective set point and control adjustments are selected, and the output sent to the appropriate valve. 

---