page_title: Productivity-improving technologies
section_title: Automation, process control and servomechanisms
hierarchical_section_title: Productivity-improving technologies / Major sources of productivity growth in economic history / Automation, process control and servomechanisms
caption_attribution_description: English: Bras robot industriel 6 axes de soudure, ARC Mate 120iC/10L de FANUC.
context_page_description: The productivity-improving technologies are the technological innovations that have historically increased productivity.
  Productivity is often measured as the ratio of output to input in the production of goods and services. Productivity is increased by lowering the amount of labor, capital, energy or materials that go into producing any given amount of economic goods and services. Increases in productivity are largely responsible for the increase in per capita living standards.
context_section_description: Automation means automatic control, meaning a process is run with minimum operator intervention.  Some of the various levels of automation are: mechanical methods, electrical relay, feedback control with a controller and computer control.  Common applications of automation are for controlling temperature, flow and pressure. Automatic speed control is important in many industrial applications, especially in sectional drives, such as found in metal rolling and paper drying. 
  The earliest applications of process control were mechanisms that adjusted the gap between mill stones for grinding grain and for keeping windmills facing into the wind.  The centrifugal governor used for adjusting the mill stones was copied by James Watt for controlling speed of steam engines in response to changes in heat load to the boiler; however, if the load on the engine changed the governor only held the speed steady at the new rate.  It took much development work to achieve the degree of steadiness necessary to operate textile machinery.  A mathematical analysis of control theory was first developed by James Clerk Maxwell.  Control theory was developed to its "classical" form by the 1950s. See: Control theory#History
  Factory electrification brought simple electrical controls such as ladder logic, whereby push buttons could be used to activate relays to engage motor starters.  Other controls such as interlocks, timers and limit switches could be added to the circuit.
  Today automation usually refers to feedback control.  An example is cruise control on a car, which applies continuous correction when a sensor on the controlled variable (Speed in this example) deviates from a set-point and can respond in a corrective manner to hold the setting.  Process control is the usual form of automation that allows industrial operations like oil refineries, steam plants generating electricity or paper mills to be run with a minimum of manpower, usually from a number of control rooms.
  The need for instrumentation grew with the rapidly growing central electric power stations after the First World War.  Instrumentation was also important for heat treating ovens, chemical plants and refineries.  Common instrumentation was for measuring temperature, pressure or flow.  Readings were typically recorded on circle charts or strip charts.  Until the 1930s control was typically "open loop", meaning that it did not use feedback.  Operators made various adjustments by such means as turning handles on valves.  If done from a control room a message could be sent to an operator in the plant by color coded light, letting him know whether to increase or decrease whatever was being controlled.  The signal lights were operated by a switchboard, which soon became automated.  Automatic control became possible with the feedback controller, which sensed the measured variable, measured the deviation from the setpoint and perhaps the rate of change and time weighted amount of deviation, compared that with the setpoint and automatically applied a calculated adjustment.  A stand-alone controller may use a combination of mechanical, pneumatic, hydraulic or electronic analogs to manipulate the controlled device.  The tendency was to use electronic controls after these were developed, but today the tendency is to use a computer to replace individual controllers.
  By the late 1930s feedback control was gaining widespread use.   Feedback control was an important technology for continuous production.
  Automation of the telephone system allowed dialing local numbers instead of having calls placed through an operator.  Further automation allowed callers to place long-distance calls by direct dial. Eventually almost all operators were replaced with automation.
  Machine tools were automated with Numerical control (NC) in the 1950s.  This soon evolved into computerized numerical control (CNC).
  Servomechanisms are commonly position or speed control devices that use feedback.  Understanding of these devices is covered in control theory.  Control theory was successfully applied to steering ships in the
caption: A set of six-axis robots used for welding.  Robots are commonly used for hazardous jobs like paint spraying, and for repetitive jobs requiring high precision such as welding and the assembly and soldering of electronics like car radios.
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