title: Star Trek: Picard (season 2)

text: The season introduces a new starship, the USS "Stargazer" (NCC-82893). Designed by Eaves, Drexler, and Blass, it was based on an earlier USS "Stargazer" (NCC-2893), the first starship that Picard captained which was introduced in the "Next Generation" episode "". The new ship retains the original "Stargazer" unique design of having four nacelles. Goldsman said they wanted to revisit the "Stargazer", which Picard has a deep emotional connection to, as part of the season's theme of looking back at the past. Blass explained that the registry for the new version was not "NCC-2893-A", following the pattern used for the USS "Enterprise" of denoting the version with a letter, because the "Stargazer" "does not hold the status in the Federation that the "Enterprise" had... the "Stargazer" didn't have that legacy". The set for the "Stargazer" bridge is wider than the bridge set for the USS "Enterprise"-E in the "Next Generation"-era films to allow for multiple widescreen cameras to film inside the set at once, though it is not as wide as the bridge set of the USS "Discovery" from "".


title: Star Trek: Picard (season 2)

text: Filming was scheduled to begin in mid-June 2020, but was delayed to January 2021 by the COVID-19 pandemic. In December 2020, Ryan said filming would begin on February 1, but on that date she revealed that it was delayed again. Principal photography began on February 16, in California where the series received tax incentives to continue filming after the first season. Doug Aarniokoski directed the first two episodes, and Crescenzo Notarile served as cinematographer after doing so for the of "Discovery". Jimmy Lindsey was also a cinematographer for the season. Location filming took place later in February at the Walt Disney Concert Hall in Los Angeles, to portray Starfleet Academy in the first episode and the Confederation Presidential Palace in the second. SoFi Stadium in Inglewood was also used to depict part of Starfleet Academy in the premiere. In April, de Lancie said scenes for the second and third seasons of "Picard" were being filmed simultaneously. Matalas and Goldsman both worked on the second season until around halfway through filming, when Matalas switched focus to the third season and Goldsman continued running the second. The two seasons had one of the largest television series crews at the time with more than 450 crewmembers.


title: Star Trek: Picard (season 2)

text: Lea Thompson directed the third and fourth episodes, including the sequence where the main cast travel back in time to 2024. This was not initially in the third episode's script when Thompson joined the series, but it was moved from the second episode to the third following rewrites. Thompson noted that she has experience working with time travel stories after starring in the "Back to the Future" film trilogy, and also acknowledged that there were existing time travel sequences in "Star Trek" that they wanted to be consistent with. The crew still wanted to put their "own spin on what it would look like going back in time", and specific visuals that Thompson added to the sequence include falling sparks "suddenly rising off the ground", a tear on Jurati's cheek moving in reverse, and footage captured by moving a camera dolly forward while zooming out which was a technique popularized by Alfred Hitchcock. Thompson spent a lot of time discussing how to light the set of "La Sirena" with Notarile due to its large size and the complex lighting needed for the time travel sequence, including flashing lights, sparks, strobes, and a representation of the ship flying close to the sun. They also had to light the set with the Borg Queen's "signature green hue" for the scene where Picard and Jurati attempt to extract information from the Borg Queen. The Markridge Industrial Tower that Raffi and Seven visit in the third episode was filmed at the Wilshire Grand Center, the tallest building in Los Angeles. The name "Markridge" is a reference to "12 Monkeys". While at the tower, Raffi detects an alien signal coming from MacArthur Park, which is where Picard's meeting with Tallinn in the fourth episode was filmed.


title: Star Trek: Picard (season 2)

text: Frequent "Star Trek" director Jonathan Frakes helmed the fifth and sixth episodes. Filming for them began by the end of June 2021. Frakes discussed the change in tone between the first and second seasons with Matalas and Goldsman, but not any changes to his own directing style. He noted that there were several parallels between the episodes and the film "Star Trek: First Contact", which he directed, and he worked with Lindsey to replicate some of the techniques that cinematographer Matthew F. Leonetti used on the film. Frakes also acknowledged the similar approach in portraying 2024 to the "Deep Space Nine" two-part episode "", which he directed half of. Frakes explained that both depictions had "a lot to do with immigration and the mistreatment of brown people... being set in 2024 serves as a cautionary tale to all of us." He felt this element of the season helped make it feel like "Star Trek" despite the contemporary setting. Frakes was excited to be working with Stewart, Spiner, and de Lancie again after he starred with them on "Next Generation", particularly highlighting the scene where Soong and Q meet in a diner. He praised Spiner and de Lancie as having "gotten better with age. There is a real confidence in the way they embrace their characters." For the scene where Q pretends to be Renée Picard's therapist, Frakes and de Lancie decided on set that the latter should use a Sigmund Freud-inspired Austrian accent. Frakes acknowledged that this was "a little on the nose" and something that Matalas and Goldsman had questioned, but they felt it was fun for the scene. The interior of the gala in these episodes was primarily filmed at the Millennium Biltmore Hotel in Downtown Los Angeles while exteriors were filmed at the Fox Theater in Westwood Village.


title: Star Trek: Picard (season 2)

text: Joe Menendez directed the seventh and eighth episodes, after previously working with Matalas on "12 Monkeys". Michael Weaver directed the ninth and tenth episodes. The use of smoke on set during the filming of the last two episodes affected Stewart's vocal cords, making his voice more hoarse than usual. The producers planned to re-record his dialogue for the episodes, but Stewart encouraged them not to do that because "the weakness in [his] voice was reflecting the weakness in the character". Filming for the season ended on September 2, and the production segued fully into filming the third season.


title: Star Trek: Picard (season 2)

text: Visual effects vendors for the season included Crafty Apes VFX, Outpost VFX, and Gradient Effects. Outpost was initially just hired to work on the "La Sirena" crash and Chateau Picard location in the third episode, but their work was expanded to include four other episodes in the season when the producers liked the results. Shots featuring Chateau Picard used aerial footage of the chateau filming location which needed to be augmented to make it look rundown for the 2024 scenes and "pristine" for the 25th century scenes. The "La Sirena" crash required fire and spark effects on the ship as well as simulations of its impact on the chateau grounds.


title: Star Trek: Picard (season 2)

text: For the fleet of starships that appear in the season premiere, Blass wanted to address fan criticisms regarding the fleet from the first-season finale in which all of the ships looked very similar. Though he knew this was done due to practical limitations in modelling that many different ships, Blass looked for a viable solution for this season and contacted the creators of the "Star Trek Online" video game about using some of their starship models. He specifically wanted to use the most popular ships from the game, as long as none of them had four nacelles so the "Stargazer" could stand out beside them. "Star Trek Online" designer and associate art director Thomas Marrone and his team provided their digital models of existing "Next Generation"-era ships (including the "Akira"-class from "Star Trek: First Contact"), their own original models of potential 25th-century ships, and some new models created specifically for the season. Marrone updated the models with more detail to match the higher quality expected for a television series, and the "Picard" visual effects team used these models in the final sequence. This meant that fan-favorite starships from the game were now franchise canon (including the "Ross"-class exploration cruiser and the "Reliant"-class light cruiser) which Marrone said was a "dream come true".


title: Star Trek: Picard (season 2)

text: The user interfaces for the starships were created by visual effects company Twisted Media, based on the LCARS computer system. They referenced the designs from "The Next Generation" and the films of that era, as well as the "" (1991) reference guide by Rick Sternbach and Michael Okuda. Okuda consulted on the company's LCARS designs, as did Drexler who also provided digital models that were integrated into the interface screens. The original plan was to mostly add the user interfaces during post-production, but this changed after Todd A. Marks and his video playback company Images on Screen joined the series. They used a combination of LG OLED screens and Screen Innovations' FlexGlass projection screens (paired with rear screen projectors) to display the interfaces on set during filming for the first and last episodes.


title: Star Trek: Picard (season 2)

text: Composer Jeff Russo said in December 2020 that he was beginning to think about the score for the season, which features an "up-tempo rearrangement" of the series' main theme. Russo did this because he wanted "a little more pace and a little more hype" to reflect the swashbuckling, action-heavy tone of the second season compared to the more contemplative first season that he originally wrote the theme for. After referencing Jerry Goldsmith's theme from "The Next Generation" and Alexander Courage's original "Star Trek" theme in his initial music for the series, Russo also references Goldsmith's "First Contact" theme in the second season's score.


title: Star Trek: Picard (season 2)

text: In Thatcher's first appearance as the punk on the bus in "The Voyage Home", the character listens to a punk rock song titled "I Hate You" that Thatcher wrote and performed with members of the film's crew. For this season, Thatcher wrote and performed a new song for the character to listen to, titled "I Still Hate You". "The Voyage Home" sound editors Mark Mangini and Aaron Glascock returned to record the new song, respectively performing guitar and drums. For Ozell's cameo appearance, she and her band perform the song "Take You Down" from her album "Overnight Lows". Menendez chose the song, which Ozell called a "strong, sassy, bluesy powerful anthem".


title: Star Trek: Picard (season 2)

text: Russo had begun recording the season's score with an orchestra at the Sony Pictures Scoring Stage by December 2021, and completed recording for the season finale on January 12, 2022. A soundtrack album was released digitally by Lakeshore Records on April 29, 2022, featuring Russo's score along with Alison Pill's version of "Shadows of the Night" from the episode "Two of One". All music by Jeff Russo, except where noted:


title: Star Trek: Picard (season 2)

text: CBS announced in June 2020 that it was participating in the "All In Challenge" to raise money for COVID-19 relief. Money donated to the campaign would go to charities including Feeding America, Meals on Wheels, World Central Kitchen, and No Kid Hungry, and fans who donated could win the chance to visit the series' set, meet Patrick Stewart, and have a walk-on role in an episode. In February 2021, Stewart appeared in a marketing campaign for Super Bowl LV advertising the rebranded streaming service Paramount+. A panel for the season was held during the "First Contact Day" virtual event on April 5, 2021, celebrating the franchise on the fictional holiday marking first contact between humans and aliens in the "Star Trek" universe. Stewart and de Lancie discussed the season at the panel, which debuted a teaser revealing the focus on time travel and the return of Q. A second teaser was released to coincide with "Capitan Picard Day" on June 16, featuring a look at de Lancie's return and teasing an alternate timeline for the characters. A teaser poster was also released featuring a contemporary-looking Los Angeles. Liz Shannon Miller of "Collider" highlighted the appearance of Q in the trailer as well as the emphasis on other characters such as Seven of Nine in alternate timeline scenarios. Matthew Jackson at "Syfy Wire" also highlighted the appearance of Q, saying it gave him goosebumps. James Whitbrook of "io9" focused on Seven of Nine appearing without her Borg implants and described the teaser poster as "cryptic".


title: Star Trek: Picard (season 2)

text: The ""Star Trek" Day" virtual event on September 8, celebrating the 55th anniversary of the "Star Trek: The Original Series" premiere, included a panel for the season where a new trailer was revealed. "io9" Germain Lussier felt it answered some questions about the season's plot, which he compared to "Back to the Future Part II" (1989), but also raised more questions. He noted that the time travelling plot allowed the season to film in modern-day Los Angeles in a similar way to "Star Trek IV: The Voyage Home". Joshua Meyer of "/Film" highlighted the reveal of the Borg Queen as well as the apparent social commentary of the trailer, including where it juxtaposes a "Nuremberg-esque rally" with images of Hong Kong in an apparent reference to the 2019–2020 Hong Kong protests. He saw this as evidence of "Picard" being the most overt of the current "Star Trek" series in its attempts at social commentary, bringing it more in-line with past "Star Trek" series. Meyer also compared the trailer's totalitarian imagery to similar scenes in "" (2015). The official trailer and key art for the season were released in January 2022 after the premiere date was revealed. Commentators said the trailer covered many of the same concepts as the previous teasers, including Q and time travel, but it also gave the first look at Goldberg's return in the season which was the highlight for many. Adam Holmes of "CinemaBlend", who believed Guinan was the most important recurring character on "The Next Generation", said the trailer "finally gives us our first taste" of Goldberg's role after she publicly agreed to return. He speculated on how the season would explain the fact that Goldberg has aged since she last portrayed Guinan despite her scenes seemingly being set in the past.


title: Star Trek: Picard (season 2)

text: Coinciding with the season's release, Paramount+ opened the "10 Forward: The Experience" pop-up event in Los Angeles on March 10, for 10 days. Each day featured a different local food truck as well as themed cocktails and the "10 Forward Canteen Store" where merchandise could be purchased. The event also featured "experiential environments", "digital interactions", and photo opportunities. Guests were encouraged to dress in cosplay. Paramount+ also brought the "10 Forward: The Experience" pop-up event to San Diego from July 21 to 24 for the 2022 San Diego Comic-Con. July 23 featured a surprise event with members of the cast. At the Las Vegas "Star Trek" convention in August, "Star Trek Wines" announced the 2401 Chateau Picard wine and a Risian wine based on those seen in "The Star Gazer". The bottles were based on scans of the props from the episode.


title: Star Trek: Picard (season 2)

text: The season premiered on March 3, 2022, on Paramount+ in the United States, and ran for 10 episodes until May 5. Each episode was broadcast in Canada by Bell Media on the same day as the U.S., on the specialty channels CTV Sci-Fi Channel (English) and Z (French) before streaming on Crave. Amazon Prime Video streamed the episodes within 24 hours of their U.S. release in over 200 other countries and territories.


title: Star Trek: Picard (season 2)

text: The season was released on DVD, Blu-Ray, and Limited Edition Steelbook formats in the U.S. on October 4, 2022. The release includes all 10 episodes, as well as deleted scenes, a gag reel, and behind-the-scenes featurettes on the creation and design of the USS "Stargazer", the making of the Chateau Picard sets, the season's props, Q's storyline with de Lancie, and the season's new prosthetics for the Borg Queen.


title: Star Trek: Picard (season 2)

text: Whip Media, who track viewership data for the 19 million worldwide users of their TV Time app, ranked "Picard" in the top 10 original streaming series for U.S. viewership each week the season was released except for the week of the season premiere. Parrot Analytics determines audience "demand expressions" based on various data sources, and the company calculated that "Picard" was the third-most in demand U.S. streaming series for March 2022 behind Disney+'s "The Mandalorian" and Netflix's "Stranger Things". This was the first time a Paramount+ series appeared in the company's monthly rankings in nine months, and they said the series was 32 times more in demand than the average U.S. streaming series. It dropped slightly to 31.4 times more in demand for April 2022, though this made it the sixth-most in demand series on Parrot's list after several new series were released. "Picard" was the ninth-most in demand series for May 2022, according to Parrot, down to 27.4 times more in demand than the average series. This was behind "", which debuted at fifth place.


title: Star Trek: Picard (season 2)

text: The review aggregator website Rotten Tomatoes reported a 85% approval score with an average rating of 7.95/10 based on 94 reviews. The website's critical consensus reads, ""Picard" gets some backup from franchise fan favorites in a sophomore season that charts a course towards recapturing more of the classical "Star Trek" spirit and makes it so." Metacritic, which uses a weighted average, assigned a score of 69 out of 100 based on reviews from 7 critics, indicating "generally favorable reviews".


title: Star Trek: Picard (season 2)

text: "IGN" gave the season a negative review saying, it "might just be the worst season of Star Trek ever produced." The review also stated that although the season "started off in a good place, looking to amend some of the missteps of the show's freshman year... in attempting to embrace and celebrate the things that fans love about Star Trek, the show fell into the trap of regurgitating old concepts."


title: Left–right political spectrum

text: The left–right political spectrum is a system of classifying political positions characteristic of left-right politics, ideologies and parties with emphasis placed upon issues of social equality and social hierarchy. In addition to positions on the left and on the right, there are centrists or moderates who are not strongly aligned with either end of the spectrum.


title: Left–right political spectrum

text: On this type of political spectrum, left-wing politics and right-wing politics are often presented as opposed, although a particular individual or group may take a left-wing stance on one matter and a right-wing stance on another; and some stances may overlap and be considered either left-wing or right-wing depending on the ideology. In France, where the terms originated, the left has been called "the party of movement" and the right "the party of order".


title: Left–right political spectrum

text: Ambrose Bierce's 1911 Devil's Dictionary characterized the right/left distinction, at the same time wryly noting each side's opinion of the other, by defining a conservative as "A statesman who is enamored of existing evils, as distinguished from the Liberal, who wishes to replace them with others."


title: Left–right political spectrum

text: The terms "left" and "right" appeared during the French Revolution of 1789 when members of the National Assembly divided into supporters of the king to the president's right and supporters of the revolution to his left. One deputy, the Baron de Gauville, explained: "We began to recognize each other: those who were loyal to religion and the king took up positions to the right of the chair so as to avoid the shouts, oaths, and indecencies that enjoyed free rein in the opposing camp".


title: Left–right political spectrum

text: When the National Assembly was replaced in 1791 by a Legislative Assembly composed of entirely new members, the divisions continued. "Innovators" sat on the left, "moderates" gathered in the centre, while the "conscientious defenders of the constitution" found themselves sitting on the right, where the defenders of the Ancien Régime had previously gathered. When the succeeding National Convention met in 1792, the seating arrangement continued, but following the coup d'état of 2 June 1793 and the arrest of the Girondins, the right side of the assembly was deserted and any remaining members who had sat there moved to the centre. However, following the Thermidorian Reaction of 1794, the members of the far left were excluded and the method of seating was abolished. The new constitution included rules for the assembly that would "break up the party groups". However, following the Restoration in 1814–1815, political clubs were again formed. The majority ultraroyalists chose to sit on the right. The "constitutionals" sat in the centre while independents sat on the left. The terms extreme right and extreme left as well as centre-right and centre-left came to be used to describe the nuances of ideology of different sections of the assembly.


title: Left–right political spectrum

text: The terms "left" and "right" were not used to refer to political ideology per se, but only to seating in the legislature. After 1848, the main opposing camps were the "democratic socialists" and the "reactionaries" who used red and white flags to identify their party affiliation. With the establishment of the Third Republic in 1871, the terms were adopted by political parties: the Republican Left, the Centre Right and the Centre Left (1871) and the Extreme Left (1876) and Radical Left (1881). The beliefs of the group called the Radical Left were actually closer to the Centre Left than the beliefs of those called the Extreme Left.


title: Left–right political spectrum

text: Beginning in the early twentieth century, the terms "left" and "right" came to be associated with specific political ideologies and were used to describe citizens' political beliefs, gradually replacing the terms "reds" and "the reaction". The words Left and Right were at first used by their opponents as slurs. Those on the Left often called themselves "republicans", which at the time meant favoring a republic over a monarchy, while those on the Right often called themselves "conservatives". By 1914, the Left half of the legislature in France was composed of Unified Socialists, Republican Socialists and Socialist Radicals, while the parties that were called "Right" now sat on the right side. The use of the words Left and Right spread from France to other countries and came to be applied to a large number of political parties worldwide, which often differed in their political beliefs. There was asymmetry in the use of the terms Left and Right by the opposing sides. The Right mostly denied that the left–right spectrum was meaningful because they saw it as artificial and damaging to unity. However, the Left, seeking to change society, promoted the distinction. As Alain observed in 1931: "When people ask me if the division between parties of the Right and parties of the Left, men of the Right and men of the Left, still makes sense, the first thing that comes to mind is that the person asking the question is certainly not a man of the Left." In British politics, the terms "right" and "left" came into common use for the first time in the late 1930s in debates over the Spanish Civil War. The Scottish sociologist Robert M. MacIver noted in "The Web of Government" (1947):


title: Left–right political spectrum

text: The right is always the party sector associated with the interests of the upper or dominant classes, the left the sector expressive of the lower economic or social classes, and the centre that of the middle classes. Historically this criterion seems acceptable. The conservative right has defended entrenched prerogatives, privileges and powers; the left has attacked them. The right has been more favorable to the aristocratic position, to the hierarchy of birth or of wealth; the left has fought for the equalization of advantage or of opportunity, for the claims of the less advantaged. Defence and attack have met, under democratic conditions, not in the name of class but in the name of principle; but the opposing principles have broadly corresponded to the interests of the different classes.


title: Left–right political spectrum

text: Generally, the left wing is characterized by an emphasis on "ideas such as freedom, equality, fraternity, rights, progress, reform and internationalism" while the right wing is characterized by an emphasis on "notions such as authority, hierarchy, order, duty, tradition, reaction and nationalism".


title: Left–right political spectrum

text: Political scientists and other analysts regard the left as including anarchists, communists, socialists, democratic socialists, social democrats, left-libertarians, progressives and social liberals. Movements for racial equality and trade unionism have also been associated with the left.


title: Left–right political spectrum

text: Political scientists and other analysts regard the right as including conservatives, right-libertarians, anarcho-capitalists, neoconservatives, imperialists, monarchists, fascists, reactionaries and traditionalists.


title: Left–right political spectrum

text: A number of significant political movements do not fit precisely into the left–right spectrum, including Christian democracy, feminism, and regionalism. Though nationalism is often regarded as a right-wing doctrine, many nationalists favor egalitarian distributions of resources. There are also "liberal nationalists" and left-wing nationalists. Populism is regarded as having both left-wing and right-wing manifestations in the form of left-wing populism and right-wing populism, respectively. Green politics is often regarded as a movement of the left, although there are also green conservatives. Andrew Dobson suggests that green politics contains an inherent conservatism as it is "adverse to anything but the most timid engineering of the social and natural world by human beings". As such, the green movement is perhaps difficult to definitively categorize as left or right.


title: Left–right political spectrum

text: Political scientists have observed that the ideologies of political parties can be mapped along a single left–right axis. Klaus von Beyme categorized European parties into nine families, which described most parties. Beyme was able to arrange seven of them from left to right: communist, socialist, green, liberal, Christian democratic, conservative and right-wing extremist. The position of agrarian and regional/ethnic parties varied. A study conducted in the late 1980s on two bases, positions on ownership of the means of production and positions on social issues, confirmed this arrangement.


title: Left–right political spectrum

text: There has been a tendency for party ideologies to persist and values and views that were present at a party's founding have survived. However, they have also adapted for pragmatic reasons, making them appear more similar. Seymour Martin Lipset and Stein Rokkan observed that modern party systems are the product of social conflicts played out in the last few centuries. They said that lines of cleavage had become "frozen".


title: Left–right political spectrum

text: The first modern political parties were liberals, organized by the middle class in the 19th century to protect them against the aristocracy. They were major political parties in that century, but declined in the twentieth century as first the working class came to support socialist parties and economic and social change eroded their middle class base. Conservative parties arose in opposition to liberals in order to defend aristocratic privilege, but in order to attract voters they became less doctrinaire than liberals. However, they were unsuccessful in most countries and generally have been able to achieve power only through cooperation with other parties.


title: Left–right political spectrum

text: Socialist parties were organized in order to achieve political rights for workers and were originally allied with liberals. However, they broke with the liberals when they sought worker control of the means of production. Christian democratic parties were organized by Catholics who saw liberalism as a threat to traditional values. Although established in the 19th century, they became a major political force following the Second World War. Communist parties emerged following a division within socialism first on support of the First World War and then support of the Bolshevik Revolution. Right-wing extremist parties are harder to define other than being more right-wing than other parties, but include fascists and some extreme conservative and nationalist parties. Green parties were the most recent of the major party groups to develop. They have mostly rejected socialism and are very liberal on social issues.


title: Left–right political spectrum

text: These categories can be applied to many parties outside of Europe. Ware (1996) asserted that in the United States both major parties were liberal, even though there are left–right policy differences between them.


title: Left–right political spectrum

text: In the 2001 book "The Government and Politics of France", Andrew Knapp and Vincent Wright say that the main factor dividing the left and right wings in Western Europe is class. The left seeks social justice through redistributive social and economic policies, while the Right defends private property and capitalism. The nature of the conflict depends on existing social and political cleavages and on the level of economic development.


title: Left–right political spectrum

text: Left-wing values include the belief in the power of human reason to achieve progress for the benefit of the human race, secularism, sovereignty exercised through the legislature, social justice and mistrust of strong personal political leadership. To the right, this is regularly seen as anti-clericalism, unrealistic social reform, doctrinaire socialism and class hatred. The Right are skeptical about the capacity for radical reforms to achieve human well-being while maintaining workplace competition.


title: Left–right political spectrum

text: The right wing believes in the established church both in itself and as an instrument of social cohesion, and they believe in the need for strong political leadership to minimize social and political divisions. To the Left, this is seen as a selfish and reactionary opposition to social justice, a wish to impose doctrinaire religion on the population and a tendency to authoritarianism and repression.


title: Left–right political spectrum

text: The differences between left and right have altered over time. The initial cleavage at the time of the French Revolution was between supporters of absolute monarchy (the Right) and those who wished to limit the king's authority (the Left). During the 19th century, the cleavage was between monarchists and republicans. Following the establishment of the Third Republic in 1871, the cleavage was between supporters of a strong executive on the Right and supporters of the primacy of the legislature on the Left.


title: Left–right political spectrum

text: A 2005 Harris Poll of American adults showed that the terms "left wing" and "right wing" were less familiar to Americans than the terms "liberal" or "conservative". Peter Berkowitz writes that in the U.S., the term "liberal" "commonly denotes the left wing of the Democratic Party" and has become synonymous with the word "progressive," a fact that is usefully contextualized for non-Americans by Ware's observation that both mainstream political parties in the United States, generally speaking, are liberal in the classic sense of the word.


title: Left–right political spectrum

text: Michael Kazin writes that the left is traditionally defined as the social movement or movements "that are dedicated to a radically egalitarian transformation of society" and suggests that many in the left in the United States who met that definition called themselves by various other terms. Kazin writes that American leftists "married the ideal of social equality to the principle of personal freedom" and that contributed to the development of important features of modern American society, including "the advocacy of equal opportunity and equal treatment for women, ethnic and racial minorities, and homosexuals; the celebration of sexual pleasure unconnected to reproduction; a media and educational system sensitive to racial and gender oppression and which celebrates what we now call multiculturalism; and the popularity of novels and films with a strongly altruistic and anti-authoritarian point of view." A variety of distinct left-wing movements existed in American history, including labor movements, the Farmer-Labor movement, various democratic socialist and socialist movements, pacifist movements, and the New Left.


title: Left–right political spectrum

text: Political scientists have frequently noted that a single left–right axis is too simplistic and insufficient for describing the existing variation in political beliefs and include other axes to compensate for this problem.


title: Left–right political spectrum

text: American libertarian writer David Boaz argued that the political terms "Left" and "Right" are used to spin a particular point of view rather than as simple descriptors, with those on the Left typically emphasizing their support for working people and accusing the Right of supporting the interests of the upper class; and those on the Right usually emphasizing their support for individualism and accusing the Left of supporting collectivism. Boaz asserts that arguments about the way these terms should be used often displace arguments about policy by raising emotional prejudice against a preconceived notion of what the terms mean.


title: Left–right political spectrum

text: In 2006, British Prime Minister Tony Blair described the main cleavage in politics as not left versus right, but open versus closed. According to Blair, attitudes towards social issues and globalism are more important than the conventional economic left–right issues. In this model, "open" voters tend to be culturally liberal, multicultural and in favour of globalisation while "closed" voters are culturally conservative, opposed to immigration and in favour of protectionism. The open–closed political spectrum has seen increased support following the rise of populist and centrist parties in the 2010s.


title: Left–right political spectrum

text: Elizabeth May, former leader of the Green Party of Canada, called the left–right political divide "something of an anachronism", arguing that "voters in modern democracies" are divided more along the lines of "'insiders' and 'outsiders.'" May cites "similarities in appeal between Donald Trump and Bernie Sanders" despite them being far apart "in policy terms".


title: Left–right political spectrum

text: Norberto Bobbio saw the polarization of the Italian Chamber of Deputies in the 1990s as evidence that the linear left–right axis remained valid. Bobbio thought that the argument that the spectrum had disappeared occurred when either the Left or Right were weak. The dominant side would claim that its ideology was the only possible one, while the weaker side would minimize its differences. He saw the Left and Right not in absolute terms, but as relative concepts that would vary over time. In his view, the left–right axis could be applied to any time period.


title: Left–right political spectrum

text: A survey of Canadian legislative caucuses conducted between 1983 and 1994 by Bob Altemeyer showed an 82% correlation between party affiliation and score on a scale for right-wing authoritarianism when comparing right-wing and social democratic caucuses. There was a wide gap between the scores of the two groups, which was filled by liberal caucuses. His survey of American legislative caucuses showed scores by American Republicans and Democrats were similar to the Canadian Right and liberals, with a 44% correlation between party affiliation and score.


title: Bijou Phillips

text: Bijou Lilly Phillips Masterson (born April 1, 1980) is an American actress, model and singer. The daughter of musician John Phillips and Geneviève Waïte, she began her career as a model. Phillips made her singing debut with "I'd Rather Eat Glass" (1999), and since her first major film appearance in "Black and White" (1999), she has acted in "Almost Famous" (2000), "Bully" (2001), "The Door in the Floor" (2004), "" (2007), and "Choke" (2008). From 2010 to 2013, she played the recurring role of Lucy Carlyle on the television series "Raising Hope".


title: Bijou Phillips

text: Phillips was born on April 1, 1980, in Greenwich, Connecticut, and is the daughter of John Phillips of The Mamas and the Papas and his third wife, Geneviève Waïte, a South African model, artist, and actress. She was named for the song "My Petite Bijou" by Lambert, Hendricks & Ross ("bijou" means 'jewel' in French). She is the youngest of Phillips's children; she has one brother, Tamerlane, and three half-siblings (Mackenzie, Jeffrey, and Chynna). After her parents split up, both were found unfit to have custody of Bijou and she was placed in foster care with a family in Bolton Landing, New York. She lived there on and off, making extended visits with her parents, who had both acquired houses in the area. Her father won custody when she was in third grade, and she moved with him to Lloyd Harbor, a village of the Town of Huntington, Long Island.


title: Bijou Phillips

text: According to Waïte, when Phillips was 13 years old, her half-sister Mackenzie informed Bijou of her (Mackenzie's) ten-year incestuous relationship with their father, and the information had a devastating effect on Bijou's teenage years, stripping her of her innocence and leaving her "wary of [her] father."


title: Bijou Phillips

text: At 14, Phillips quit school and moved into her own apartment with a housekeeper, just off Fifth Avenue. Once described by "The Observer" as a "wild child", she experienced a rebellious childhood in New York City, where she used to party, drink and take drugs, such as cocaine, ecstasy, and heroin. On this period of her life, she remarked: "If you were 14 years old and able to live on your own in an apartment in New York City, and you got invited to all these clubs, and you got a bank account and you had a car service you could call so that you could go wherever you wanted ... What would happen?". At 15, she reportedly lost her virginity to singer Evan Dando. Growing up, she became somewhat of a local tabloids' fixture due to her late-night persona and association with other socialites like sisters Paris and Nicky Hilton. At 17, following the death of her friend, the 20-year-old Manhattan socialite Davide Sorrenti, due to a heroin overdose, her father sent her into rehab.


title: Bijou Phillips

text: Phillips was on the cover of "Interview" magazine when she was 13. Shortly thereafter, she appeared on the cover of "Vogue Italia". Phillips also became an image model for Calvin Klein and appeared in several advertising campaigns in which adolescents showed white underwear. The campaigns were widely condemned as eerily pedophilic. She has expressed her distaste for the modeling world, and once stated in an interview: "It was like, I wanted to go swimming in the ocean, but I was jumping up and down in a puddle."


title: Bijou Phillips

text: After signing a record deal at age 17, Phillips began working on her debut album "I'd Rather Eat Glass", produced by Jerry Harrison. It was released on May 11, 1999, by Almo Sounds, and remains her only full-length music release to date. The album's title refers to her past as a fashion model, saying she would "rather eat glass" than go back to modeling. Phillips collaborated with a number of artists when writing songs for the album, including Eric Bazilian, Greg Wells, Dave Bassett, Howard Jones and Jill Cunniff. Upon its release, "I'd Rather Eat Glass" received mixed reviews from music critics, mostly criticising the work for being immature, but her musical style has been positively compared to Natalie Imbruglia or Kay Hanley of Letters to Cleo.


title: Bijou Phillips

text: Phillips made her film debut in a brief role of the independent drama "Sugar Town" (1999). Her first major film role came the same year, as an Upper East Side girl trying to fit in with the black hip-hop crowd, in James Toback's drama "Black and White", opposite Robert Downey Jr., Jared Leto, Brooke Shields and Elijah Wood. The film received mixed reviews and found a limited audience in theaters, but "AllMovie" remarked: "[The film] starts off strong with a provocative performance by newcomer Bijou Phillips as the most unapologetic seeker of approval from her hip-hop-loving friends. Phillips eventually fades into the background, and the film becomes hampered by Toback's insistence upon grafting a standard crime-drama plot".


title: Bijou Phillips

text: Phillips appeared with Kate Hudson in Cameron Crowe's semi-biographical musical drama "Almost Famous" (2000). The film was a success and received four Academy Awards nominations. 2001 saw Phillips star in two independent coming-of-age films. In "Tart", opposite Dominique Swain and Melanie Griffith, she played the longtime friend of a young woman at a preparatory school in 1980s New York City. "PopMatters" found Phillips to be one of the only intriguing actors in the film, "thanks to yet another fearless performance". In "Bully", based on the 1993 murder of Bobby Kent, she took on the role of one in a group of several young adults in South Florida who enact a murder plot against a mutual friend who has emotionally, physically and sexually abused them for years. The film had a mixed critical response, but famed critic Roger Ebert was one of its notable admirers and gave it four out of four stars. Her performance in the film led "The Hollywood Reporter" to name her one of 2002's "Shooting Stars of Tomorrow".


title: Bijou Phillips

text: In 2003, Phillips starred as a member of a bizarre cult of young criminals, alongside Mischa Barton, in the thriller "Octane", which premiered at the Cannes Film Festival. In 2004, she played the nanny of an author's young daughter, with Jeff Bridges and Kim Basinger, in "The Door in the Floor" (2004), a drama with heavy sexual themes adapted from the novel "A Widow for One Year" by John Irving. Phillips starred with Anne Hathaway in the drama "Havoc" (2005) as a spoiled socialite, appearing nude in some of its scenes. "ViewLondon" wrote that the "supporting cast are superb, particularly Bijou Phillips" as the "trashy best friend", while "Variety" asserted: "As played by Hathaway and Phillips, the friendship between [their characters] rings girlish and true, and comes complete with tantalizing, lesbian-flavored moments". "Havoc" was not released in theaters in the United States due to unfavorable critical reception. She appeared as an ill-fated high school senior in the slasher film "Venom" (also 2005), produced by Kevin Williamson.


title: Bijou Phillips

text: In 2007, Phillips starred in the independent horror film "The Wizard of Gore", as the girlfriend of a magic magazine's publisher, and collaborated with actress Lauren German in three films, the first being the comedy drama "Spin", about seven people at a popular Los Angeles nightclub. In "", which served as a sequel to "Hostel" (2005), Phillips starred as one of three American female art students in Rome who are directed to a Slovak village where they are kidnapped and taken to a facility in which rich clients pay to torture and kill people. She claimed that her torture sequence, which entails her being scalped by a power saw, required around forty-five setups. "I don't think I could do something like this again", she stated in a 2007 interview. "I'm glad that I had the experience, and I love my job, but we went into places that I didn't know existed, and I don't need to do that again." Banned from theatrical release in several countries, "Hostel: Part II" was released theatrically in the United States, to lackluster box office returns.


title: Bijou Phillips

text: The biographical film "What We Do Is Secret" featured Phillips as Lorna Doom, the Germs' bassist and a close friend of singer Darby Crash. Director Rodger Grossman cast Phillips when she was 17 years old, and she stayed committed to the project for the entire time it took to bring the film into production, which was almost one decade. She received critical acclaim for her portrayal; Phil Gallo for "Variety" found her performance to be "striking" and stated that her character "lights up in a unique way whenever she's in Crash's company or simply talking about him." In 2008, Phillips appeared in the documentary "Chelsea on the Rocks", about the Hotel Chelsea, directed by Abel Ferrara, and starred as a milkmaid, opposite Sam Rockwell and Anjelica Huston, in the well-received black comedy "Choke", based on the Chuck Palahniuk's novel of the same name. In "Dark Streets" (her last 2008 film), Phillips played a love interest and the alluring star singer of a club in 1930s New York City.


title: Bijou Phillips

text: In 2009, Phillips had starring roles in four independent feature films, three of which were opposite Danny Masterson. Her first release in the year was the romantic comedy "Wake", in which she played an emotionally isolated, modern woman who meets a man mourning his fiancée at a funeral. The horror film "It's Alive", a remake of the 1974 film of the same name written and directed by Larry Cohen, saw Phillips star as a mother who has a murderous baby. "Dread Central", in its review for the film, noted: "Bijou Philips is undoubtedly the star here, jumping into her role in what is admittedly just a piece of schlock cinema with great aplomb". In the comedy "Made for Each Other", Phillips would reunite with Lauren German and also play a woman whose husband decides the only way to morally rectify his cheating is to get his wife to cheat on him. Her last 2009 film was the crime drama "The Bridge to Nowhere", portraying a sex worker.


title: Bijou Phillips

text: In FOX's sitcom "Raising Hope" (2010–2014), Phillips played the title character's biological mother, and a serial killer sentenced to death. Until its finale, she appeared in a total of seven episodes of the series. In 2010 and 2012, she guest-starred in episodes of the police procedural television series "Hawaii Five-0" and "", and in 2011 she appeared in the video for Broken Social Scene's song "Sweetest Kill". Phillips has not acted since her last appearance in "Raising Hope", opting to focus on her family and health.


title: Bijou Phillips

text: Phillips dated Sean Lennon at some point in the mid-2000s and she became the muse and subject matter of his 2006 album "Friendly Fire".


title: Bijou Phillips

text: In 2004, Phillips began dating Danny Masterson; the couple met at a poker tournament in Las Vegas. They are both Scientologists. The couple announced their engagement in March 2009. They were married on October 18, 2011, in a private castle in Ireland. On February 14, 2014, Phillips gave birth to their daughter.


title: Bijou Phillips

text: On February 17, 2017, Masterson revealed that Phillips had been suffering from kidney disease for five years. She was born with small kidneys and had been battling the disease by living a stress-free life, eating a vegan diet, and getting dialysis. She suffered from a blood infection and was in need of a transplant. On April 7, 2017, she received a kidney transplant.


title: Bijou Phillips

text: In November 2017, actor Daniel Franzese alleged that Phillips had "ridiculed" him about his sexuality and weight and physically assaulted him on the set of "Bully". Phillips subsequently apologized for her behavior. The same month, actress Heather Matarazzo claimed that Phillips had held her against a wall and choked her shortly before filming for "" began.


title: Bijou Phillips

text: Phillips has defended both her father and her husband (the former accused of rape and incest by Phillips's half-sister Mackenzie; the latter accused of rape and sexual assault by multiple women) in the face of allegations of sexual abuse.


title: Bijou Phillips

text: Of Mackenzie's allegations against their father, Phillips said, "I'm 29 now, I've talked to everyone who was around during that time, I've asked the hard questions. I do not believe my sister. Our father [was] many things. This is not one of them." In contrast, Phillips also stated that Mackenzie told her about their incestuous relationship, and that the news was "confusing and scary" and that she was "heartbroken" to think that her family left her alone with her father. In a 2000 interview with Bruce LaBruce she discussed a song she had written about her father with the refrain, "He touched me wrong," but didn't go into detail about whether the lyrics referred to herself or someone else.


title: Bijou Phillips

text: Between 2017 and 2020, Phillips's husband Danny Masterson was accused of rape, harassment and stalking of several women (including Chrissie Carnell-Bixler, the wife of musician Cedric Bixler-Zavala). Masterson has not responded directly to any of the allegations, but on Instagram, Phillips mocked Carnell-Bixler's police report detailing Masterson's alleged rape.


title: The Impossible (2012 film)

text: The Impossible () is a 2012 English-language Spanish disaster drama film directed by J. A. Bayona and written by Sergio G. Sánchez. It is based on the experience of María Belón and her family in the 2004 Indian Ocean tsunami. It features an international cast including Naomi Watts, Ewan McGregor and Tom Holland in his film debut.


title: The Impossible (2012 film)

text: The film received positive reviews from critics for its direction and its acting, especially for Watts who was nominated for the Academy Award for Best Actress, the Golden Globe Award for Best Actress – Motion Picture Drama, and a Screen Actors Guild Award for Outstanding Performance by a Female Actor in a Leading Role.


title: The Impossible (2012 film)

text: In 2004, Doctor Maria Bennett, her husband Henry, and their three sons Lucas, Simon and Thomas go on a Christmas holiday to Khao Lak, Thailand. Arriving on Christmas Eve, they settle in and begin to enjoy the brand new Orchid Beach Resort. Two days later on December 26, the massive Indian Ocean tsunami inundates the area.


title: The Impossible (2012 film)

text: Maria and Lucas eventually emerge from the swirling water and find one another, with Maria having sustained serious injuries to her leg and chest. They help a toddler, Daniel, from the debris and are soon found by locals who dress and transfer them to a hospital in the city of Takua Pa. Daniel is separated from them during the journey. At the hospital, Maria encourages Lucas to help others find their family members while she goes into surgery for her chest injuries.


title: The Impossible (2012 film)

text: Meanwhile, Henry and the two younger boys have also survived and are together. Henry leaves Simon and Thomas with another family who are then taken to the mountains for safety by local relief crews. Henry stays behind to search for Maria and Lucas in the rubble. While out looking, injured and alone, he is picked up by a passer-by and driven to a nearby bus station with other survivors.


title: The Impossible (2012 film)

text: Communication facilities are scarce, but a European tourist named Karl, who has also been separated from his family, lends Henry his cell phone to contact his relatives in England. Henry promises Maria's father he will look everywhere for his family and that he will find them. Karl volunteers to accompany Henry to look for Maria and Lucas as well as his own family, who were at the beach when the tsunami hit.


title: The Impossible (2012 film)

text: While Maria is in surgery, her medical chart is mixed up with a patient named Muriel Barnes, who has died. Lucas returns to find his mother's bed empty and is then taken to a tent where children without families are kept safe. The mistake is discovered when Lucas cannot identify any of the dead woman's jewelry and he is subsequently reunited with his mother, who had been moved to a private room in the ICU. While he waits in the hospital, Lucas sees Daniel, who has been reunited with his father.


title: The Impossible (2012 film)

text: Henry and Karl search for their families in various places before they arrive at the hospital, where Henry is given five minutes to look. Karl gives him a piece of paper with the names of his family members.


title: The Impossible (2012 film)

text: A vehicle carrying Simon and Thomas also stops outside the hospital, and the boys get off so Thomas can urinate. From a distance, Lucas recognizes his father, and while searching for him in the chaotic crowd outside, Lucas's brothers spot him and they reunite. Henry finds the three of them together. He learns that Maria is in the hospital, ready to undergo more surgery for her leg.


title: The Impossible (2012 film)

text: As the anesthesia puts her to sleep, Maria experiences flashbacks of how she came to be injured and how she surfaced the water. While she is in surgery, Lucas tells Henry he has something really important to tell Maria.


title: The Impossible (2012 film)

text: The following day, the family boards an ambulance airplane to Singapore so Maria may receive further medical treatment. A representative from their insurance company, Zurich Insurance, assures them everything will be taken care of as Lucas sees countless people outside the hospital looking through patient lists. On the plane, Lucas tells his mother that Daniel is safe with his father. Maria cries and looks out the window at the chaos left behind as the plane takes off.


title: The Impossible (2012 film)

text: The film was a co-production of Spanish film companies Apaches Entertainment and Telecinco Cinema, and employed much of the crew from "The Orphanage", including the director, writer, production manager, cinematographer, composer, and editor. Filmed between the Ciudad de la Luz studio in Alicante (Spain) and Thailand. Principal photography began 23 August 2010 in Alicante and continued in October in Thailand.


title: The Impossible (2012 film)

text: Director Juan Antonio Bayona decided not to specify the nationalities of the main characters in order to create a universal film in which nationalities were irrelevant to the plot.


title: The Impossible (2012 film)

text: The tsunami was recreated with a mixture of digital effects and real water surges filmed in slow motion created in a water tank in Spain using miniatures that were destroyed by a huge wave. Bayona committed to working with real water rather than a computer-generated wave because he wanted the story to be authentic. This meant Watts and Holland spent five weeks filming physically and psychologically demanding scenes in a massive water tank. Holland, aged 14 at the time of filming, later described it as a "scary environment ...You can imagine how tiring and brutal that was."


title: The Impossible (2012 film)

text: Warner Bros. Pictures released the film in Spain on 11 October 2012. The United States distribution rights were pre-bought by Summit Entertainment. A teaser trailer was released on 26 December 2011. After a full-length English language trailer was released on 20 August 2012, a United States release date of 21 December 2012 was confirmed by Summit. It was released on 11 October 2012 in Spain and in Ireland and the United Kingdom on 1 January 2013. The film was released in the United States on 4 January 2013 and was made available by Summit Entertainment through a website streaming the film to members of SAG-AFTRA for consideration of the SAG awards.


title: The Impossible (2012 film)

text: It was released on DVD/Blu-ray in the United States and Canada on Tuesday, 19 March 2013, with a European release 13 May 2013.


title: The Impossible (2012 film)

text: Review aggregation website Rotten Tomatoes gave the film an approval rating of 81% based on 202 reviews, with an average rating of 7.3/10. The site's critical consensus reads, "The screenplay isn't quite as powerful as the direction or the acting, but with such an astonishing real-life story at its center, "The Impossible" is never less than compelling." At Metacritic, which assigns a weighted mean rating to reviews, the film had an average score of 73 out of 100, based on 42 critics, indicating "generally favourable reviews."


title: The Impossible (2012 film)

text: Roger Ebert of the "Chicago Sun-Times" gave a perfect four-star rating, praising the performances of Watts and McGregor, and the direction of Bayona. He called it "one of the best films of the year".


title: The Impossible (2012 film)

text: Deborah Young of "The Hollywood Reporter" gave a very positive review, praising the performances of the two leading stars, stating that "Watts packs a huge charge of emotion as the battered, ever-weakening Maria whose tears of pain and fear never appear fake or idealised. McGregor, cut and streaked with excessive blood he seems too distraught to wash away, keeps the tension razor-sharp as he pursues his family in a vast, shattered landscape." About the film she added, ""The Impossible" is one of the most emotionally realistic disaster movies in recent memory – and certainly one of the most frightening in its epic re-creation of the catastrophic 2004 Indian Ocean tsunami."


title: The Impossible (2012 film)

text: Justin Chang of "Variety" magazine gave a positive review, praising Bayona's directing and Sánchez's writing: "Collaborating again after their impressive 2007 debut feature, "The Orphanage", Bayona and Sanchez get many things right here, starting with their decision to eschew a more panoramic view of the disaster to follow one family's journey from start to finish." About the performances of the main cast members he added, "Watts has few equals at conveying physical and emotional extremes, something she again demonstrates in a mostly bedridden role, and McGregor, in one of his better recent performances, manages to turn a simple phone call home into a small aria of heartbreak. Holland, in his live-action bigscreen debut, is wonderful as a kind, somewhat short-tempered kid who still has plenty to learn, setting the tone for similarly heartrending turns by young Joslin and Pendergast."


title: The Impossible (2012 film)

text: Damon Wise of "The Guardian" gave the film four stars out of five. He also praised the performances, stating that "as Maria, Watts is both brave and vulnerable, and her scenes with the young Lucas (the excellent Tom Holland) are among the film's best, with adult and child now unexpected equals, the mother humbled, the son rising to the challenge. McGregor, meanwhile, gives one of his best performances as the sad and desperate Henry, trying to play the hero, the provider, while knowing his cause is almost certainly lost." About the film, he added: "Part of the appeal of this affecting and powerful drama is that it puts the viewer right in the moment at every stage, using authentic locations and tsunami survivors to hammer home the reality of this tragedy."


title: The Impossible (2012 film)

text: Eric Kohn of "IndieWire" gave the film a "B−" grade and stated that the film "suffers from the greater problem of emphasising a feel-good plot within the context of mass destruction."


title: The Impossible (2012 film)

text: According to "The New York Times" reviewer A. O. Scott, this narrowly-defined cinematic framing of the disaster through European and not Thai lenses represents "a troubling complacency and a lack of compassion in "The Impossible"," a movie which he found to be "less an examination of mass destruction than the tale of a spoiled holiday."


title: The Impossible (2012 film)

text: Simon Jenkins, a British survivor from Portsmouth, wrote to "The Guardian", stating the film is "beautifully accurate". This was in response to critics commenting that the film is "overdramatic" and "whitewashed". He says of the comments, "As I must, I've never been the sort of person to revisit and analyse events of the past, but some of these articles frustrated me. Had this film been purely about the tale of a western middle class family's 'ruined' holiday then I would have agreed. For me, it was the exact opposite. Rather than concentrating on the 'privileged white visitors', the film portrayed the profound sense of community and unity that I experienced in Thailand, with this family at the centre of it. Both for my (then) 16-year-old self and the Belón family, it was the Thai people who waded through the settled water after the first wave had struck to help individuals and families... The Thai people had just lost everything – homes, businesses, families – yet their instinct was to help the tourists."


title: The Impossible (2012 film)

text: "The Impossible" was a box office success. In Spain the film was released on 11 October 2012, and opened in 638 cinemas, grossing $11,569,306 on its opening weekend, ranking No. 1 with a per-cinema average of $18,134, the highest-grossing opening weekend for a film in Spain. On its second weekend the film remained at No. 1 and grossed $9,016,065 with a per-cinema average of $14,022. On its third weekend it remained at No. 1 and made $5,768,184 with a per-cinema average of $9,098. The film ended up earning $54,536,668 at the Spanish box office and $180,274,123 worldwide, compared with its estimated $45 million production budget.


title: PID controller

text: A proportional–integral–derivative controller (PID controller or three-term controller) is a control loop mechanism employing feedback that is widely used in industrial control systems and a variety of other applications requiring continuously modulated control. A PID controller continuously calculates an "error value" formula_1 as the difference between a desired setpoint (SP) and a measured process variable (PV) and applies a correction based on proportional, integral, and derivative terms (denoted "P", "I", and "D" respectively), hence the name.


title: PID controller

text: In practical terms, PID automatically applies an accurate and responsive correction to a control function. An everyday example is the cruise control on a car, where ascending a hill would lower speed if constant engine power were applied. The controller's PID algorithm restores the measured speed to the desired speed with minimal delay and overshoot by increasing the power output of the engine in a controlled manner.


title: PID controller

text: The first theoretical analysis and practical application of PID was in the field of automatic steering systems for ships, developed from the early 1920s onwards. It was then used for automatic process control in the manufacturing industry, where it was widely implemented in at first pneumatic and then electronic controllers. Today the PID concept is used universally in applications requiring accurate and optimized automatic control.


title: PID controller

text: The distinguishing feature of the PID controller is the ability to use the three "control terms" of proportional, integral and derivative influence on the controller output to apply accurate and optimal control. The block diagram on the right shows the principles of how these terms are generated and applied. It shows a PID controller, which continuously calculates an "error value" formula_1 as the difference between a desired setpoint formula_3 and a measured process variable formula_4: formula_5, and applies a correction based on proportional, integral, and derivative terms. The controller attempts to minimize the error over time by adjustment of a "control variable" formula_6, such as the opening of a control valve, to a new value determined by a weighted sum of the control terms.


title: PID controller

text: Tuning – The balance of these effects is achieved by loop tuning to produce the optimal control function. The tuning constants are shown below as "K" and must be derived for each control application, as they depend on the response characteristics of the complete loop external to the controller. These are dependent on the behavior of the measuring sensor, the final control element (such as a control valve), any control signal delays and the process itself. Approximate values of constants can usually be initially entered knowing the type of application, but they are normally refined, or tuned, by "bumping" the process in practice by introducing a setpoint change and observing the system response.


title: PID controller

text: Control action – The mathematical model and practical loop above both use a "direct" control action for all the terms, which means an increasing positive error results in an increasing positive control output correction. The system is called "reverse" acting if it is necessary to apply negative corrective action. For instance, if the valve in the flow loop was 100–0% valve opening for 0–100% control output – meaning that the controller action has to be reversed. Some process control schemes and final control elements require this reverse action. An example would be a valve for cooling water, where the fail-safe mode, in the case of loss of signal, would be 100% opening of the valve; therefore 0% controller output needs to cause 100% valve opening.


title: PID controller

text: where formula_9, formula_10, and formula_11, all non-negative, denote the coefficients for the proportional, integral, and derivative terms respectively (sometimes denoted "P", "I", and "D").


title: PID controller

text: In the "standard form" of the equation (see later in article), formula_10 and formula_11 are respectively replaced by formula_14 and formula_15; the advantage of this being that formula_16 and formula_17 have some understandable physical meaning, as they represent an integration time and a derivative time respectively. formula_15 is the time constant with which the controller will attempt to approach the set point. formula_14 determines how long the controller will tolerate the output being consistently above or below the set point.


title: PID controller

text: Although a PID controller has three control terms, some applications need only one or two terms to provide appropriate control. This is achieved by setting the unused parameters to zero and is called a PI, PD, P or I controller in the absence of the other control actions. PI controllers are fairly common in applications where derivative action would be sensitive to measurement noise, but the integral term is often needed for the system to reach its target value.


title: PID controller

text: The use of the PID algorithm does not guarantee optimal control of the system or its control stability . Situations may occur where there are excessive delays: the measurement of the process value is delayed, or the control action does not apply quickly enough. In these cases lead–lag compensation is required to be effective. The response of the controller can be described in terms of its responsiveness to an error, the degree to which the system overshoots a setpoint, and the degree of any system oscillation. But the PID controller is broadly applicable since it relies only on the response of the measured process variable, not on knowledge or a model of the underlying process.


title: PID controller

text: Continuous control, before PID controllers were fully understood and implemented, has one of its origins in the centrifugal governor, which uses rotating weights to control a process. This was invented by Christiaan Huygens in the 17th century to regulate the gap between millstones in windmills depending on the speed of rotation, and thereby compensate for the variable speed of grain feed.


title: PID controller

text: With the invention of the low-pressure stationary steam engine there was a need for automatic speed control, and James Watt’s self-designed "conical pendulum" governor, a set of revolving steel balls attached to a vertical spindle by link arms, came to be an industry standard. This was based on the millstone-gap control concept.


title: PID controller

text: Rotating-governor speed control, however, was still variable under conditions of varying load, where the shortcoming of what is now known as proportional control alone was evident. The error between the desired speed and the actual speed would increase with increasing load. In the 19th century, the theoretical basis for the operation of governors was first described by James Clerk Maxwell in 1868 in his now-famous paper "On Governors". He explored the mathematical basis for control stability, and progressed a good way towards a solution, but made an appeal for mathematicians to examine the problem. The problem was examined further in 1874 by Edward Routh, Charles Sturm, and in 1895, Adolf Hurwitz, all of whom contributed to the establishment of control stability criteria.


title: PID controller

text: In subsequent applications, speed governors were further refined, notably by American scientist Willard Gibbs, who in 1872 theoretically analyzed Watt's conical pendulum governor.


title: PID controller

text: About this time, the invention of the Whitehead torpedo posed a control problem that required accurate control of the running depth. Use of a depth pressure sensor alone proved inadequate, and a pendulum that measured the fore and aft pitch of the torpedo was combined with depth measurement to become the pendulum-and-hydrostat control. Pressure control provided only a proportional control that, if the control gain was too high, would become unstable and go into overshoot with considerable instability of depth-holding. The pendulum added what is now known as derivative control, which damped the oscillations by detecting the torpedo dive/climb angle and thereby the rate-of-change of depth. This development (named by Whitehead as "The Secret" to give no clue to its action) was around 1868.


title: PID controller

text: Another early example of a PID-type controller was developed by Elmer Sperry in 1911 for ship steering, though his work was intuitive rather than mathematically-based.


title: PID controller

text: It was not until 1922, however, that a formal control law for what we now call PID or three-term control was first developed using theoretical analysis, by Russian American engineer Nicolas Minorsky. 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; this was then given a mathematical treatment by Minorsky.


title: PID controller

text: 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), which required adding the integral term. Finally, the derivative term was added to improve stability and control.


title: PID controller

text: Trials were carried out on the USS "New Mexico", with the controllers controlling the "angular velocity" (not the angle) of the rudder. PI control yielded sustained yaw (angular error) of ±2°. Adding the D element yielded a yaw error of ±1/6°, better than most helmsmen could achieve.


title: PID controller

text: The Navy ultimately did not adopt the system due to resistance by personnel. Similar work was carried out and published by several others in the 1930s.


title: PID controller

text: 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 Black in the late 1920s, but not published until 1934. 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. The integral term was called "Reset". Later the derivative term was added by a further bellows and adjustable orifice.


title: PID controller

text: 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 hazardous locations. They were the industry standard for many decades until the advent of discrete electronic controllers and distributed control systems (DCSs).


title: PID controller

text: With these controllers, a pneumatic industry signaling standard of was established, which had an elevated zero to ensure devices were working within their linear characteristic and represented the control range of 0-100%.


title: PID controller

text: 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.


title: PID controller

text: Most modern PID controls in industry are implemented as computer software in DCSs, programmable logic controllers (PLCs), or discrete compact controllers.


title: PID controller

text: Electronic analog PID control loops were often found within more complex electronic systems, for example, the head positioning of a disk drive, the power conditioning of a power supply, or even the movement-detection circuit of a modern seismometer. Discrete electronic analog controllers have been largely replaced by digital controllers using microcontrollers or FPGAs to implement PID algorithms. However, discrete analog PID controllers are still used in niche applications requiring high-bandwidth and low-noise performance, such as laser-diode controllers.


title: PID controller

text: Consider a robotic arm that can be moved and positioned by a control loop. An electric motor may lift or lower the arm, depending on forward or reverse power applied, but power cannot be a simple function of position because of the inertial mass of the arm, forces due to gravity, external forces on the arm such as a load to lift or work to be done on an external object.


title: PID controller

text: By measuring the position (PV), and subtracting it from the setpoint (SP), the error (e) is found, and from it the controller calculates how much electric current to supply to the motor (MV).


title: PID controller

text: The obvious method is proportional control: the motor current is set in proportion to the existing error. However, this method fails if, for instance, the arm has to lift different weights: a greater weight needs a greater force applied for the same error on the down side, but a smaller force if the error is low on the upside. That's where the integral and derivative terms play their part.


title: PID controller

text: An integral term increases action in relation not only to the error but also the time for which it has persisted. So, if the applied force is not enough to bring the error to zero, this force will be increased as time passes. A pure "I" controller could bring the error to zero, but it would be both slow reacting at the start (because the action would be small at the beginning, depending on time to get significant) and brutal at the end (the action increases as long as the error is positive, even if the error has started to approach zero).


title: PID controller

text: Applying too much integral when the error is small and decreasing will lead to overshoot. After overshooting, if the controller were to apply a large correction in the opposite direction and repeatedly overshoot the desired position, the output would oscillate around the setpoint in either a constant, growing, or decaying sinusoid. If the amplitude of the oscillations increases with time, the system is unstable. If they decrease, the system is stable. If the oscillations remain at a constant magnitude, the system is marginally stable.


title: PID controller

text: A derivative term does not consider the magnitude of the error (meaning it cannot bring it to zero: a pure D controller cannot bring the system to its setpoint), but the rate of change of error, trying to bring this rate to zero. It aims at flattening the error trajectory into a horizontal line, damping the force applied, and so reduces overshoot (error on the other side because of too great applied force).


title: PID controller

text: In the interest of achieving a controlled arrival at the desired position (SP) in a timely and accurate way, the controlled system needs to be critically damped. A well-tuned position control system will also apply the necessary currents to the controlled motor so that the arm pushes and pulls as necessary to resist external forces trying to move it away from the required position. The setpoint itself may be generated by an external system, such as a PLC or other computer system, so that it continuously varies depending on the work that the robotic arm is expected to do. A well-tuned PID control system will enable the arm to meet these changing requirements to the best of its capabilities.


title: PID controller

text: If a controller starts from a stable state with zero error (PV = SP), then further changes by the controller will be in response to changes in other measured or unmeasured inputs to the process that affect the process, and hence the PV. Variables that affect the process other than the MV are known as disturbances. Generally, controllers are used to reject disturbances and to implement setpoint changes. A change in load on the arm constitutes a disturbance to the robot arm control process.


title: PID controller

text: In theory, a controller can be used to control any process that has a measurable output (PV), a known ideal value for that output (SP), and an input to the process (MV) that will affect the relevant PV. Controllers are used in industry to regulate temperature, pressure, force, feed rate, flow rate, chemical composition (component concentrations), weight, position, speed, and practically every other variable for which a measurement exists.


title: PID controller

text: The PID control scheme is named after its three correcting terms, whose sum constitutes the manipulated variable (MV). The proportional, integral, and derivative terms are summed to calculate the output of the PID controller. Defining formula_6 as the controller output, the final form of the PID algorithm is


title: PID controller

text: The proportional term produces an output value that is proportional to the current error value. The proportional response can be adjusted by multiplying the error by a constant "K", called the proportional gain constant.


title: PID controller

text: A high proportional gain results in a large change in the output for a given change in the error. If the proportional gain is too high, the system can become unstable (see the section on loop tuning). In contrast, a small gain results in a small output response to a large input error, and a less responsive or less sensitive controller. If the proportional gain is too low, the control action may be too small when responding to system disturbances. Tuning theory and industrial practice indicate that the proportional term should contribute the bulk of the output change.


title: PID controller

text: The steady-state error is the difference between the desired final output and the actual one. Because a non-zero error is required to drive it, a proportional controller generally operates with a steady-state error. Steady-state error (SSE) is proportional to the process gain and inversely proportional to proportional gain. SSE may be mitigated by adding a compensating bias term to the setpoint AND output or corrected dynamically by adding an integral term.


title: PID controller

text: The contribution from the integral term is proportional to both the magnitude of the error and the duration of the error. The integral in a PID controller is the sum of the instantaneous error over time and gives the accumulated offset that should have been corrected previously. The accumulated error is then multiplied by the integral gain ("K") and added to the controller output.


title: PID controller

text: The integral term accelerates the movement of the process towards setpoint and eliminates the residual steady-state error that occurs with a pure proportional controller. However, since the integral term responds to accumulated errors from the past, it can cause the present value to overshoot the setpoint value (see the section on loop tuning).


title: PID controller

text: The derivative of the process error is calculated by determining the slope of the error over time and multiplying this rate of change by the derivative gain "K". The magnitude of the contribution of the derivative term to the overall control action is termed the derivative gain, "K".


title: PID controller

text: Derivative action predicts system behavior and thus improves settling time and stability of the system. An ideal derivative is not causal, so that implementations of PID controllers include an additional low-pass filtering for the derivative term to limit the high-frequency gain and noise. Derivative action is seldom used in practice though – by one estimate in only 25% of deployed controllers – because of its variable impact on system stability in real-world applications.


title: PID controller

text: "Tuning" a control loop is the adjustment of its control parameters (proportional band/gain, integral gain/reset, derivative gain/rate) to the optimum values for the desired control response. Stability (no unbounded oscillation) is a basic requirement, but beyond that, different systems have different behavior, different applications have different requirements, and requirements may conflict with one another.


title: PID controller

text: Even though there are only three parameters and it is simple to describe in principle, PID tuning is a difficult problem because it must satisfy complex criteria within the limitations of PID control. Accordingly, there are various methods for loop tuning, and more sophisticated techniques are the subject of patents; this section describes some traditional, manual methods for loop tuning.


title: PID controller

text: Designing and tuning a PID controller appears to be conceptually intuitive, but can be hard in practice, if multiple (and often conflicting) objectives, such as short transient and high stability, are to be achieved. PID controllers often provide acceptable control using default tunings, but performance can generally be improved by careful tuning, and performance may be unacceptable with poor tuning. Usually, initial designs need to be adjusted repeatedly through computer simulations until the closed-loop system performs or compromises as desired.


title: PID controller

text: Some processes have a degree of nonlinearity, so parameters that work well at full-load conditions do not work when the process is starting up from no load. This can be corrected by gain scheduling (using different parameters in different operating regions).


title: PID controller

text: If the PID controller parameters (the gains of the proportional, integral and derivative terms) are chosen incorrectly, the controlled process input can be unstable; i.e., its output diverges, with or without oscillation, and is limited only by saturation or mechanical breakage. Instability is caused by "excess" gain, particularly in the presence of significant lag.


title: PID controller

text: Generally, stabilization of response is required and the process must not oscillate for any combination of process conditions and setpoints, though sometimes marginal stability (bounded oscillation) is acceptable or desired.


title: PID controller

text: where formula_36 is the PID transfer function and formula_37 is the plant transfer function. A system is "unstable" where the closed loop transfer function diverges for some formula_31. This happens in situations where formula_39. Typically, this happens when formula_40 with a 180-degree phase shift. Stability is guaranteed when formula_41 for frequencies that suffer high phase shifts. A more general formalism of this effect is known as the Nyquist stability criterion.


title: PID controller

text: Two basic requirements are "regulation" (disturbance rejection – staying at a given setpoint) and "command tracking" (implementing setpoint changes). These terms refer to how well the controlled variable tracks the desired value. Specific criteria for command tracking include rise time and settling time. Some processes must not allow an overshoot of the process variable beyond the setpoint if, for example, this would be unsafe. Other processes must minimize the energy expended in reaching a new setpoint.


title: PID controller

text: There are several methods for tuning a PID loop. The most effective methods generally involve developing some form of process model and then choosing P, I, and D based on the dynamic model parameters. Manual tuning methods can be relatively time-consuming, particularly for systems with long loop times.


title: PID controller

text: The choice of method depends largely on whether the loop can be taken offline for tuning, and on the response time of the system. If the system can be taken offline, the best tuning method often involves subjecting the system to a step change in input, measuring the output as a function of time, and using this response to determine the control parameters.


title: PID controller

text: If the system must remain online, one tuning method is to first set formula_42 and formula_43 values to zero. Increase the formula_44 until the output of the loop oscillates; then set formula_44 to approximately half that value for a "quarter amplitude decay"-type response. Then increase formula_42 until any offset is corrected in sufficient time for the process, but not until too great a value causes instability. Finally, increase formula_43, if required, until the loop is acceptably quick to reach its reference after a load disturbance. Too much formula_43 causes excessive response and overshoot. A fast PID loop tuning usually overshoots slightly to reach the setpoint more quickly; however, some systems cannot accept overshoot, in which case an overdamped closed-loop system is required, which in turn requires a formula_44 setting significantly less than half that of the formula_44 setting that was causing oscillation.


title: PID controller

text: Another heuristic tuning method is known as the Ziegler–Nichols method, introduced by John G. Ziegler and Nathaniel B. Nichols in the 1940s. As in the method above, the formula_42 and formula_43 gains are first set to zero. The proportional gain is increased until it reaches the ultimate gain, formula_53, at which the output of the loop starts to oscillate constantly. formula_53 and the oscillation period formula_55 are used to set the gains as follows:


title: PID controller

text: These gains apply to the ideal, parallel form of the PID controller. When applied to the standard PID form, only the integral and derivative gains formula_42 and formula_43 are dependent on the oscillation period formula_55.


title: PID controller

text: This method was developed in 1953 and is based on a first-order + time delay model. Similar to the Ziegler–Nichols method, a set of tuning parameters were developed to yield a closed-loop response with a decay ratio of formula_59. Arguably the biggest problem with these parameters is that a small change in the process parameters could potentially cause a closed-loop system to become unstable.


title: PID controller

text: Published in 1984 by Karl Johan Åström and Tore Hägglund, the relay method temporarily operates the process using bang-bang control and measures the resultant oscillations. The output is switched (as if by a relay, hence the name) between two values of the control variable. The values must be chosen so the process will cross the setpoint, but they need not be 0% and 100%; by choosing suitable values, dangerous oscillations can be avoided.


title: PID controller

text: As long as the process variable is below the setpoint, the control output is set to the higher value. As soon as it rises above the setpoint, the control output is set to the lower value. Ideally, the output waveform is nearly square, spending equal time above and below the setpoint. The period and amplitude of the resultant oscillations are measured, and used to compute the ultimate gain and period, which are then fed into the Ziegler–Nichols method.


title: PID controller

text: Specifically, the ultimate period formula_55 is assumed to be equal to the observed period, and the ultimate gain is computed as formula_61 where is the amplitude of the process variable oscillation, and is the amplitude of the control output change which caused it.


title: PID controller

text: where k is the process gain, τ is the time constant, θ is the dead time, and u(s) is a step change input. Converting this transfer function to the time domain results in:


title: PID controller

text: It is important when using this method to apply a large enough step change input that the output can be measured; however, too large of a step change can affect the process stability. Additionally, a larger step change ensures that the output does not change due to a disturbance (for best results, try to minimize disturbances when performing the step test).


title: PID controller

text: One way to determine the parameters for the first-order process is using the 63.2% method. In this method, the process gain (k) is equal to the change in output divided by the change in input. The dead time (θ) is the amount of time between when the step change occurred and when the output first changed. The time constant (τ) is the amount of time it takes for the output to reach 63.2% of the new steady-state value after the step change. One downside to using this method is that it can take a while to reach a new steady-state value if the process has large time constants.


title: PID controller

text: Most modern industrial facilities no longer tune loops using the manual calculation methods shown above. Instead, PID tuning and loop optimization software are used to ensure consistent results. These software packages gather data, develop process models, and suggest optimal tuning. Some software packages can even develop tuning by gathering data from reference changes.


title: PID controller

text: Mathematical PID loop tuning induces an impulse in the system and then uses the controlled system's frequency response to design the PID loop values. In loops with response times of several minutes, mathematical loop tuning is recommended, because trial and error can take days just to find a stable set of loop values. Optimal values are harder to find. Some digital loop controllers offer a self-tuning feature in which very small setpoint changes are sent to the process, allowing the controller itself to calculate optimal tuning values.


title: PID controller

text: Another approach calculates initial values via the Ziegler–Nichols method, and uses a numerical optimization technique to find better PID coefficients.


title: PID controller

text: Other formulas are available to tune the loop according to different performance criteria. Many patented formulas are now embedded within PID tuning software and hardware modules.


title: PID controller

text: Advances in automated PID loop tuning software also deliver algorithms for tuning PID Loops in a dynamic or non-steady state (NSS) scenario. The software models the dynamics of a process, through a disturbance, and calculate PID control parameters in response.


title: PID controller

text: While PID controllers are applicable to many control problems, and often perform satisfactorily without any improvements or only coarse tuning, they can perform poorly in some applications and do not in general provide "optimal" control. The fundamental difficulty with PID control is that it is a feedback control system, with "constant" parameters, and no direct knowledge of the process, and thus overall performance is reactive and a compromise. While PID control is the best controller in an observer without a model of the process, better performance can be obtained by overtly modeling the actor of the process without resorting to an observer.


title: PID controller

text: PID controllers, when used alone, can give poor performance when the PID loop gains must be reduced so that the control system does not overshoot, oscillate or hunt about the control setpoint value. They also have difficulties in the presence of non-linearities, may trade-off regulation versus response time, do not react to changing process behavior (say, the process changes after it has warmed up), and have lag in responding to large disturbances.


title: PID controller

text: The most significant improvement is to incorporate feed-forward control with knowledge about the system, and using the PID only to control error. Alternatively, PIDs can be modified in more minor ways, such as by changing the parameters (either gain scheduling in different use cases or adaptively modifying them based on performance), improving measurement (higher sampling rate, precision, and accuracy, and low-pass filtering if necessary), or cascading multiple PID controllers.


title: PID controller

text: PID controllers work best when the loop to be controlled is linear and symmetric. Thus, their performance in non-linear and asymmetric systems is degraded.


title: PID controller

text: A non-linear valve, for instance, in a flow control application, will result in variable loop sensitivity, requiring dampened action to prevent instability. One solution is the use of the valve's non-linear characteristic in the control algorithm to compensate for this.


title: PID controller

text: An asymmetric application, for example, is temperature control in HVAC systems using only active heating (via a heating element), where there is only passive cooling available. When it is desired to lower the controlled temperature the heating output is off, but there is no active cooling due to control output. Any overshoot of rising temperature can therefore only be corrected slowly; it cannot be forced downward by the control output. In this case the PID controller could be tuned to be over-damped, to prevent or reduce overshoot, but this reduces performance by increasing the settling time of a rising temperature to the set point. The inherent degradation of control quality in this application could be solved by application of active cooling.


title: PID controller

text: A problem with the derivative term is that it amplifies higher frequency measurement or process noise that can cause large amounts of change in the output. It is often helpful to filter the measurements with a low-pass filter in order to remove higher-frequency noise components. As low-pass filtering and derivative control can cancel each other out, the amount of filtering is limited. Therefore, low noise instrumentation can be important. A nonlinear median filter may be used, which improves the filtering efficiency and practical performance. In some cases, the differential band can be turned off with little loss of control. This is equivalent to using the PID controller as a PI controller.


title: PID controller

text: The basic PID algorithm presents some challenges in control applications that have been addressed by minor modifications to the PID form.


title: PID controller

text: One common problem resulting from the ideal PID implementations is integral windup. Following a large change in setpoint the integral term can accumulate an error larger than the maximal value for the regulation variable (windup), thus the system overshoots and continues to increase until this accumulated error is unwound. This problem can be addressed by:


title: PID controller

text: For example, a PID loop is used to control the temperature of an electric resistance furnace where the system has stabilized. Now when the door is opened and something cold is put into the furnace the temperature drops below the setpoint. The integral function of the controller tends to compensate for error by introducing another error in the positive direction. This overshoot can be avoided by freezing of the integral function after the opening of the door for the time the control loop typically needs to reheat the furnace.


title: PID controller

text: A PI controller (proportional-integral controller) is a special case of the PID controller in which the derivative (D) of the error is not used.


title: PID controller

text: A PI controller can be modelled easily in software such as Simulink or Xcos using a "flow chart" box involving Laplace operators:


title: PID controller

text: Setting a value for formula_70 is often a trade off between decreasing overshoot and increasing settling time.


title: PID controller

text: The lack of derivative action may make the system more steady in the steady state in the case of noisy data. This is because derivative action is more sensitive to higher-frequency terms in the inputs.