Editing Proportional–integral–derivative controller (section)

===Industrial control===
[[File:Nozzle and flapper proportional controller.png|thumb|Proportional control using nozzle and flapper high gain amplifier and negative feedback]]
The wide use of feedback controllers did not become feasible until the development of wideband high-gain amplifiers to use the concept of [[negative feedback]]. This had been developed in telephone engineering electronics by [[Harold Stephen Black|Harold Black]] in the late 1920s, but not published until 1934.<ref name="ben96" /> Independently, Clesson E Mason of the Foxboro Company in 1930 invented a wide-band pneumatic controller by combining the [[nozzle and flapper]] high-gain pneumatic amplifier, which had been invented in 1914, with negative feedback from the controller output. This dramatically increased the linear range of operation of the nozzle and flapper amplifier, and integral control could also be added by the use of a precision bleed valve and a bellows generating the integral term. The result was the "Stabilog" controller which gave both proportional and integral functions using feedback bellows.<ref name="ben96" /> The integral term was called ''Reset''.<ref>{{citation|last=Shinskey|first=F Greg|title=The power of external-reset feedback|publisher=Control Global|year=2004|url=https://classes.engineering.wustl.edu/2009/spring/che433/2009-LAB/Control%20Theory/external-reset.pdf}}</ref>  Later the derivative term was added by a further bellows and adjustable orifice.

From about 1932 onwards, the use of wideband pneumatic controllers increased rapidly in a variety of control applications. Air pressure was used for generating the controller output, and also for powering process modulating devices such as diaphragm-operated control valves.  They were simple low maintenance devices that operated well in harsh industrial environments and did not present explosion risks in [[Electrical equipment in hazardous areas|hazardous locations]]. They were the industry standard for many decades until the advent of discrete electronic controllers and [[distributed control system]]s (DCSs).

With these controllers, a pneumatic industry signaling standard of {{cvt|3|-|15|psi|bar|1}} was established, which had an elevated zero to ensure devices were working within their linear characteristic and represented the control range of 0-100%.

[[File:DTK4848V01.jpg|thumb|Typical setup for temperature controlling process. From left to right: [[resistance thermometer]], Delta DTK4848V01 temperature controller with PID function, a [[solid-state relay]]]]

In the 1950s, when high gain electronic amplifiers became cheap and reliable, electronic PID controllers became popular, and the pneumatic standard was emulated by 10-50 mA and 4–20 mA [[current loop]] signals (the latter became the industry standard). Pneumatic field actuators are still widely used because of the advantages of pneumatic energy for control valves in process plant environments.
[[File:Analogue control loop evolution.png|thumb|Showing the evolution of analog control loop signaling from the pneumatic to the electronic eras]]
[[File:Smart current loop positioner.png|thumb|Current loops used for sensing and control signals. A modern electronic "smart" valve positioner is shown, which will incorporate its own PID controller.]]

Most modern PID controls in industry are implemented as [[computer software]] in DCSs, [[programmable logic controller]]s (PLCs), or discrete [[compact controller]]s.