From fly-balls to microchips
By C.J. Acker, Westinghouse Electric Corp., and Richard Colborn, Systems Consulting Inc.
Through Power Engineering`s 100-year history, control technology has evolved from simple, elegantly designed nineteenth-century mechanical devices to mind-boggling advanced computer technology. Today`s Westinghouse Process Control Division traces its ancestry through a century of control advancements, from fly-ball turbine governors (Figure 1) to advanced microprocessor technologies. It`s a history that follows the paths of two industry leaders, Westinghouse and the Hagan Controls Co.
Founded in 1886 by inventor George Westinghouse, The Westinghouse Electric Corp. became a world leader in the design and manufacture of generators, turbines, motors and a host of other industrial products. The Hagan Co., founded three decades later in 1916, also assumed a leadership role in combustion control and instrumentation technologies. Through the next five decades, Westinghouse and Hagan often worked together to meet their customers` needs while remaining focused on different aspects of power generation control technology. That changed in 1963 when Westinghouse and Hagan Controls combined forces and together launched a new era of computerized, plant-wide control systems technologies.
Hagan–controlling the furnace
The Hagan story began shortly before the United States entered World War I. George Hagan and John Hopwood had organized the George J. Hagan Co. in 1916 to manufacture stokers and automatic controls. Two years later, Hopwood and his close friend and associate Thomas A. Peebles acquired the controls portion of the business and incorporated it as the Hagan Corp., with Hopwood serving as president.
The company prospered in the combustion control and instrumentation field and acquired the first U.S. patents covering forced-draft furnace pressure control and equal division of load among boilers in service. Hagan boiler control equipment was quite sophisticated for its time and was capable of making fine adjustments in response to changing load demand. Hagan systems were the first in the United States to allow the efficient use of blast furnace gas, and their master regulator boiler controls, balanced float regulators and roto-reciprocating valves became standards in the industry.
As boiler control technology moved through the hydraulic and pneumatic stages of development from 1920 to the early 1950s, the Hagan Co. made major contributions with many products. These included master senders, ratio relays and regulators, compensating relays, diaphragm-type regulators, transfer valves, fuel- and air-control relays, the ring balance meter and a host of other products.
Westinghouse–controlling the turbine
By the time Hagan Controls Co. was founded, Westinghouse had al ready accumulated a quarter century of experience in the design and manufacture of steam-turbine generators. Westinghouse turbines employed fly-ball governors, an elegantly simple, direct mechanical linkage device that had been used since the days of James Watt to regulate steam flow in proportion to load. But as Westinghouse`s steam turbine-generators grew ever larger and more complex to meet the demands of the electric utility industry, new methods of controlling steam flow and turbine speed were required. The simple mechanical fly-ball governor could not provide the actuation force necessary to make adjustments to the much larger steam valves in these new designs. By 1916, Westinghouse engineers had developed a method to overcome this limitation. By incorporating hydraulic servo-motors with the fly-ball governor, they were able to significantly amplify the force of the speed signal and provide the higher actuation power necessary for large steam control valves.
Within a decade, however, the size of utility turbines continued to grow, inexorably pushing the theoretical limits of even the hydraulically augmented fly-ball governor`s capabilities. In 1930, Westinghouse engineers again overcame that size limitation with a revolutionary new design–the first internal, mechanical-hydraulic (MH) turbine control system. This MH system utilized an integral steam-driven impeller to control pressure in a fully hydraulic valve control mechanism. This design gave Westinghouse a unique advantage over competitors in developing even larger steam turbine designs for the rapidly growing electric utility industry. For the next 40 years, the MH controller remained the industry standard.
The electronic age
In the years after World War II, both Westinghouse and Hagan began developing expertise in the burgeoning field of electronics. Hagan`s instrumentation and control systems gradually migrated from basic hydraulic/pneumatic controls to electronic controls. Westinghouse was heavily involved in developing electronic capabilities in that period as well. Its efforts focused on advancements in radar and communications technologies, designing electronic controllers for industrial applications and, in a presage to future developments, basic research in computer technologies.
By the late 1950s, both Hagan and Westinghouse used magnetic amplifiers as solid state electronic controllers, and both were recognized for their high reliability standards. A Westinghouse magnetic amplifier, designated “CYPAK,” was widely applied in the steel industry beginning in 1955. Meanwhile, Hagan`s “PowrMAG” was the first such device used in the utility industry, at the H.B. Robinson Station of Carolina Power and Light Co. in 1958. The magnetic amplifier, coupled with an extensive line of electro-pneumatic instrumentation, pneumatic drives, chart recorders and other devices gave Hagan a major technological advantage.
Hagan`s focus through this period remained on boiler and furnace control products for the steel and electric utility markets. Westinghouse, on the other hand, recognized a growing need to bring the accuracy, reliability and flexibility of electronic systems to plant-wide control applications. That need stemmed from several factors:
z Plant systems had become too large to be effectively controlled with pneumatic control systems.
z The time lag for metering response had become too great for accurate control.
z Volume boosters used to speed up response time were very expensive.
Westinghouse also recognized the potential of using a common electronic control technology in different applications. The same electronics that could control a boiler could also control a turbine, blast furnace, caster or other large industrial process. Between 1950 and 1960, Westinghouse`s work in automatic steel mill controls led to the development and successful application of one of the first direct digital control (DDC) process computers–the PRODAC 4449. The PRODAC introduced several novel concepts to industrial computing such as “priority interrupts” and separate central processing units for mathematics and control logic. It also incorporated discrete logic devices with transistor switching speeds of three microseconds. Four of these revolutionary systems were shipped to steel companies in 1960-61. The last of these systems was taken out of service in 1983 after more than 20 years of service. Westinghouse subsequently succeeded in applying the concept to utility applications in the form of a computer called the PRODAC IV, at the Sewaren Plant of Public Service Electric and Gas.
The success of these systems confirmed Westinghouse`s strategy of providing a common computer platform for a variety of applications, and spurred the development of the PRODAC-500 process control computer which incorporated a new line of input/output and a number of internal improvements. Recognizing the potential for a smaller system for controlling individual processes, Westinghouse designed a scaled version of the PRODAC-500, and in the process developed the world`s first mini-computer, the P-50. Ironically, while among the first digital controls ever developed, many of the original P-50s are still in operation, a testament to their overall design and fundamental reliability. Through the 1960s and 70s, new models were introduced including the P-250, P-550, P-2000, W-2000 and W-2500 systems. These process computers were applied to a wide range of applications from steam and gas turbine control to steel mill controls, chemical processing, energy management and plant computer systems in nuclear power plants.
Recognizing that their individual capabilities in utility control complemented each other, Hagan and Westinghouse had been bidding jointly on a number of power plant projects in the early 1960s. These projects typically featured Westinghouse process computer systems that incorporated Hagan boiler controls, digital logic and final control elements. This partnership culminated in 1963 when Westinghouse purchased the Controls Division of Hagan Chemicals and Controls Inc., along with the Hagan name and the expertise of some 500 Hagan employees. Combined with the Westinghouse Computer Systems department, the resulting organization quickly introduced a series of new technologies and applications including the first “printed circuit card” transistorized electronic boiler controls in 1966 for Arkansas Power & Light Co.`s Ritchie No. 2 Station.
Another system, a combination of transistorized controls and Hagan`s PowrMAG, was installed at Pennsylvania Electric Co.`s Homer City plant in 1969 and at New England Power Co.`s Brayton Point Station. This combination incorporated a “Plant Unit Master” and marked the first complete integration of boiler and turbine controls in a single coordinated logic system.
In 1972, the next generation of printed circuit card systems was introduced. Designated the Westinghouse 7300 System, it was among the first power plant control systems in the industry to employ programmable logic and to use a redundant, diode-switched, single-level dc power supply. The 7300 system was first installed at Virginia Electric Power Co.`s Yorktown Station and later became the primary choice for both process control and reactor protection at more than 40 nuclear power stations in the United States, Europe and Asia. The 7300 Series was one of the most successful control technologies ever introduced. Nearly 20 years after the last of these workhorse systems was manufactured, more than 100 are still in full operation.
Westinghouse continued its development work in both analog and direct digital control areas and ultimately became a leader in applying advanced control technologies for utility applications. In 1969, the venerable MH turbine controller was replaced with the first application of the analog electro-hydraulic control system. Within two years, digital electro-hydraulic turbine controls were introduced using a series of Westinghouse computers, including the P-2000 and W-2500.
The microprocessor revolution
While new developments in control technology mushroomed in the 1960s and early 70s, they paled in comparison to what lay ahead. The emergence of microprocessors in the mid 1970s revolutionized computer technology and with it the process control industry. In a few years, computing power and speed were increasing at exponential rates, with equally dramatic reductions in computing costs. How significant was the microprocessor revolution? Consider this. The magnetic core memory modules used on vintage P-50 computers weighed approximately two pounds, had a stor age capacity of approximately 7,000 bytes of data and cost about $4,000 per unit in 1960s dollars. Today, a fingernail-sized memory chip, one of many used on current systems, offers more than one million bytes of data storage for less than $2.
In the process control industry, the emergence of microprocessor technology led to an entirely new concept–the distributed control system (DCS). DCS architecture replaced the single-function, centralized process computer with a network of low-cost, microprocessor-based controllers. Benefits of the DCS architecture include: elimination of a central point of failure; physical and functional separation of control areas; lower installation costs; the ability to incorporate system-wide redundancy; built-in self diagnostics; ease of system expansion or upgrade; the ability to quickly change or modify control strategies; and overall system reliability exceeding 99 percent.
In the late 1970s, Westinghouse initiated development of a powerful, multi-function DCS system designated WDPF, or the Westinghouse Distributed Processing Family. Since its introduction in 1981, thousands of WDPF systems have been installed in power plants, steel mills, water and wastewater treatment plants, and a host of other industrial process facilities. A significant advantage of the DCS architecture is its ability to easily incorporate new features, components and technology developments, evolving in a modular fashion without disrupting the underlying system structure. Today`s technology options include advanced UNIX workstations or commercially available PCs for operator interfaces, the latest generation of high-speed processors, optical disk mass storage and retrieval, on-line process trending packages, prioritized “intelligent” alarming programs and the incorporation of a host of sophisticated software applications ranging from economic modeling to expert systems.
DCS technology has also moved well beyond traditional process-control applications. With the ability to move data in real time from individual processes to local- and wide-area computer networks, sophisticated distributed control systems have become an integral part of the rapidly advancing information technology arena–the merging of process and plant data with business-wide information systems.
Past as prologue
If the past is an accurate predictor, control technology will continue to evolve at warp speed–a prospect that may create apprehension for those investing large sums in new systems. In the last several years, however, a trend known as open computing has emerged that bodes well for both users and suppliers of control systems technologies. Open computing involves the introduction of recognized standards, both formal and de-facto, that provide a framework for future development. An analogy to open computing is the standards for electrical distribution and transmission, mostly established when the fly-ball governor was still an advanced control technology. While electrical standards define the physical and functional bounds to which manufactures must conform (voltage, frequency, plug and socket types, etc.), the application layer is wide open for new developments over time. For instance, a 1920s vintage vacuum-tube radio or a 1990s compact-disc player will both operate on the same power system.
Similar trends are developing in the computing and control technology arena where standards are taking hold in real-time computer operating systems and communications protocols. With open standards, users will be better able to preserve their system investment over time, more easily incorporate incremental upgrades to newer technologies and avoid the risk of relying on a single vendor`s proprietary technology. Control systems suppliers will also reap many similar benefits. They will be able to focus on development of advanced applications and performance improvement features in a much more predictable and stable environment. They will lower their risk of being frozen out of the market by a single dominant competing technology or finding themselves dependent on a single vendor`s proprie tary product.
As we enter the 21st century, digital control system technology, in many respects, is just now coming of age. Computer power and speed is creating the potential for applications and control strategies that would have been considered science fiction just a few years ago. Neural networks–software applications that “learn” and become more capable over time–are beginning to be applied in distributed control systems. Sophisticated artificial intelligence applications are also under development, as are fuzzy-logic programs that strive to “predict” seemingly random events by employing advanced chaos theory mathematics.
Looking to the future, it is important to consider lessons from the past. The evolution from the simple fly-ball governor to the microprocessor occurred in the span of a single lifetime. The history of Westinghouse and Hagan demonstrate that control technology has continually evolved in order to keep pace with advancements in plant and process equipment. They had to respond to ever-changing needs, keep pace with technology developments and meet the demands of industry for ever-increasing productivity and efficiency. Exactly what forms control technology will assume in the future is anyone`s guess. But it seems likely that a century from now, readers of Power Engineering`s bi-centennial edition will look back with nostalgia at those simple, “elegantly designed,” but thoroughly obsolete 1990s microprocessors. z
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On the left is a magnetic core memory module used on Westinghouse P-50 process control computers in the 1960s.
Memory size 64,000 bits
Clock speed 0.2 MHz
Cost (1966) $4,000.00
On the right is a controller memory chip currently used in Westinghouse WDPF Distributed Control Systems.
Memory size 1,000,000 bytes (dynamic RAM)
Clock speed 66 MHz
(Left) State-of-the-art control technology
(Above) 1940s-style control room with pneumatic control systems