Editing Industrial process control (section)

==History==
Early process control breakthroughs came most frequently in the form of water control devices. [[Ktesibios of Alexandria]] is credited for inventing float valves to regulate water level of [[water clock]]s in the 3rd century BC. In the 1st century AD, [[Heron of Alexandria]] invented a water valve similar to the fill valve used in modern toilets.<ref name="Young etal">{{cite book|last1=Young|first1=William Y|last2=Svrcek|first2=Donald P|last3=Mahoney|first3=Brent R|title=A Real Time Approach to Process Control|date=2014|publisher=John Wiley & Sons Inc.|location=Chichester, West Sussex, United Kingdom|isbn=978-1119993872|pages=1–2|edition=3|chapter=1: A Brief History of Control and Simulation}}</ref>

Later process controls inventions involved basic physics principles. In 1620, [[Cornelis Drebbel]] invented a bimetallic thermostat for controlling the temperature in a furnace. In 1681, [[Denis Papin]] discovered the pressure inside a vessel could be regulated by placing weights on top of the vessel lid.<ref name = 'Young etal'/> In 1745, Edmund Lee created the [[windmill fantail|fantail]] to improve windmill efficiency; a fantail was a smaller windmill placed 90° of the larger fans to keep the face of the windmill pointed directly into the oncoming wind.

With the dawn of the Industrial Revolution in the 1760s, process controls inventions were aimed to replace human operators with mechanized processes.  In 1784, [[Oliver Evans]] created a water-powered flourmill which operated using buckets and screw conveyors. [[Henry Ford]] applied the same theory in 1910 when the assembly line was created to decrease human intervention in the automobile production process.<ref name = 'Young etal'/>

For continuously variable process control it was not until 1922 that a formal control law for what we now call [[PID control]] or three-term control was first developed using theoretical analysis, by [[Russian American]] engineer [[Nicolas Minorsky]].<ref>{{cite journal |last=Minorsky |first=Nicolas |author-link=Nicolas Minorsky |title=Directional stability of automatically steered bodies |journal=Journal of the American Society for Naval Engineers |year=1922 |volume=34 |pages=280–309 |issue=2 |doi=10.1111/j.1559-3584.1922.tb04958.x}}</ref> Minorsky was researching and designing automatic ship steering for the US Navy and based his analysis on observations of a [[helmsman]]. He noted the helmsman steered the ship based not only on the current course error, but also on past error, as well as the current rate of change;<ref>{{cite book|title=A History of Control Engineering 1930-1955 |last=Bennett |first= Stuart |year=1993 |publisher =Peter Peregrinus Ltd. On behalf of the Institution of Electrical Engineers |location= London |isbn= 978-0-86341-280-6 |url=https://books.google.com/books?id=VD_b81J3yFoC&pg=PA67 |page= 67}}</ref> this was then given a mathematical treatment by Minorsky.<ref name="ben96">{{cite journal
| journal = IEEE Control Systems Magazine
| volume = 16
| issue = 3
| last = Bennett
| first = Stuart
| title = A brief history of automatic control
| year = 1996
| url = http://ieeecss.org/CSM/library/1996/june1996/02-HistoryofAutoCtrl.pdf
| pages = 17–25
| doi = 10.1109/37.506394
| access-date = 2018-03-25
| archive-url = https://web.archive.org/web/20160809050823/http://ieeecss.org/CSM/library/1996/june1996/02-HistoryofAutoCtrl.pdf
| archive-date = 2016-08-09
| url-status = dead
}}</ref>
His goal was stability, not general control, which simplified the problem significantly. While proportional control provided stability against small disturbances, it was insufficient for dealing with a steady disturbance, notably a stiff [[gale]] (due to [[#Steady-state error|steady-state error]]), which required adding the integral term. Finally, the derivative term was added to improve stability and control.