{"id":71,"date":"2021-02-12T20:00:16","date_gmt":"2021-02-13T01:00:16","guid":{"rendered":"https:\/\/opentextbc.ca\/basichvac\/chapter\/thermocouple\/"},"modified":"2023-03-02T11:40:57","modified_gmt":"2023-03-02T16:40:57","slug":"thermocouple","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/basichvac\/chapter\/thermocouple\/","title":{"raw":"Thermocouples","rendered":"Thermocouples"},"content":{"raw":"Click play on the following audio player to listen along as you read this section.\r\n\r\nhttps:\/\/media.bccampus.ca\/id\/0_y1si44r4?width=608&amp;height=80&amp;playerId=23449753\r\n\r\nA <strong>[pb_glossary id=\"208\"]thermocouple[\/pb_glossary]<\/strong> is constructed from two dissimilar metals that utilize thermoelectric generation to create a small voltage when heated. When one junction is subjected to presence of heat at the pilot light flame, a small DC current flows through the cold junction of the thermocouple, which is connected to the pilot safety shut-off gas valve circuit.\r\n\r\n[caption id=\"attachment_70\" align=\"aligncenter\" width=\"710\"]<img class=\"wp-image-70 size-full\" src=\"https:\/\/opentextbc.ca\/accessibilitytoolkit\/wp-content\/uploads\/sites\/336\/2021\/02\/Thermocouple-Circuit.png\" alt=\"\" width=\"710\" height=\"424\" \/> Thermocouple and pilot light safety control circuit.[\/caption]\r\n\r\nIf the pilot flame is extinguished, the voltage source disappears and the normally closed, held-open valve re-closes, thus preventing gas from filling the space.\r\n\r\nThis small value of voltage, usually around 25 \u2013 30 DC millivolts, provides the power to hold the pilot light valve open during normal operation. The types of metals used in the construction of the thermocouple depend upon the values of temperature they are to be subjected to.\r\n\r\nIf a higher value of voltage is required, a <strong>[pb_glossary id=\"209\"]thermopile[\/pb_glossary]<\/strong>, which is manufactured from several <strong>[pb_glossary id=\"210\"]series-aiding[\/pb_glossary]<\/strong> connected thermocouples, can provide voltages of typically 250 DC millivolts or 750 DC millivolts. Certain stand-alone gas fired furnaces and fire-places will utilize a <strong>[pb_glossary id=\"209\"]thermopile[\/pb_glossary] <\/strong>to provide control circuit power to a low-voltage thermostat installed in the room.","rendered":"<p>Click play on the following audio player to listen along as you read this section.<\/p>\n<p><iframe loading=\"lazy\" id=\"kaltura_player\" title=\"2.19 Thermocouples.mp3\" src=\"https:\/\/api.ca.kaltura.com\/p\/148\/sp\/14800\/embedIframeJs\/uiconf_id\/23449753\/partner_id\/148?iframeembed=true&#38;playerId=kaltura_player&#38;entry_id=0_y1si44r4&#38;flashvars[leadWithHTML5]=true&#38;flashvars[streamerType]=auto&#38;flashvars[localizationCode]=en&#38;flashvars[sideBarContainer.plugin]=true&#38;flashvars[sideBarContainer.position]=left&#38;flashvars[sideBarContainer.clickToClose]=true&#38;flashvars[chapters.plugin]=true&#38;flashvars[chapters.layout]=vertical&#38;flashvars[chapters.thumbnailRotator]=false&#38;flashvars[streamSelector.plugin]=true&#38;flashvars[EmbedPlayer.SpinnerTarget]=videoHolder&#38;flashvars[dualScreen.plugin]=true&#38;flashvars[Kaltura.addCrossoriginToIframe]=true&#38;wid=0_ekcvepwo\" width=\"608\" height=\"80\" allowfullscreen=\"allowfullscreen\" sandbox=\"allow-downloads allow-forms allow-same-origin allow-scripts allow-top-navigation allow-pointer-lock allow-popups allow-modals allow-orientation-lock allow-popups-to-escape-sandbox allow-presentation allow-top-navigation-by-user-activation\" frameborder=\"0\"><\/iframe><\/p>\n<p>A <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_71_208\">thermocouple<\/a><\/strong> is constructed from two dissimilar metals that utilize thermoelectric generation to create a small voltage when heated. When one junction is subjected to presence of heat at the pilot light flame, a small DC current flows through the cold junction of the thermocouple, which is connected to the pilot safety shut-off gas valve circuit.<\/p>\n<figure id=\"attachment_70\" aria-describedby=\"caption-attachment-70\" style=\"width: 710px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-70 size-full\" src=\"https:\/\/opentextbc.ca\/accessibilitytoolkit\/wp-content\/uploads\/sites\/336\/2021\/02\/Thermocouple-Circuit.png\" alt=\"\" width=\"710\" height=\"424\" srcset=\"https:\/\/opentextbc.ca\/basichvac\/wp-content\/uploads\/sites\/336\/2021\/02\/Thermocouple-Circuit.png 710w, https:\/\/opentextbc.ca\/basichvac\/wp-content\/uploads\/sites\/336\/2021\/02\/Thermocouple-Circuit-300x179.png 300w, https:\/\/opentextbc.ca\/basichvac\/wp-content\/uploads\/sites\/336\/2021\/02\/Thermocouple-Circuit-65x39.png 65w, https:\/\/opentextbc.ca\/basichvac\/wp-content\/uploads\/sites\/336\/2021\/02\/Thermocouple-Circuit-225x134.png 225w, https:\/\/opentextbc.ca\/basichvac\/wp-content\/uploads\/sites\/336\/2021\/02\/Thermocouple-Circuit-350x209.png 350w\" sizes=\"auto, (max-width: 710px) 100vw, 710px\" \/><figcaption id=\"caption-attachment-70\" class=\"wp-caption-text\">Thermocouple and pilot light safety control circuit.<\/figcaption><\/figure>\n<p>If the pilot flame is extinguished, the voltage source disappears and the normally closed, held-open valve re-closes, thus preventing gas from filling the space.<\/p>\n<p>This small value of voltage, usually around 25 \u2013 30 DC millivolts, provides the power to hold the pilot light valve open during normal operation. The types of metals used in the construction of the thermocouple depend upon the values of temperature they are to be subjected to.<\/p>\n<p>If a higher value of voltage is required, a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_71_209\">thermopile<\/a><\/strong>, which is manufactured from several <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_71_210\">series-aiding<\/a><\/strong> connected thermocouples, can provide voltages of typically 250 DC millivolts or 750 DC millivolts. Certain stand-alone gas fired furnaces and fire-places will utilize a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_71_209\">thermopile<\/a> <\/strong>to provide control circuit power to a low-voltage thermostat installed in the room.<\/p>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_71_208\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_71_208\"><div tabindex=\"-1\"><p>A device made of two dissimilar metals, which produce a DC voltage of approximately 25 \u2013 30 millivolts\u00a0 when one end is subjected to heat.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_71_209\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_71_209\"><div tabindex=\"-1\"><p>Several thermocouples connected together to provide a higher value of DC voltage. Typically either 250 or 750 DC millivolts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_71_210\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_71_210\"><div tabindex=\"-1\"><p>When multiple voltage sources are connected so that their potential differences add together, providing a higher voltage than any one individual device<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":90,"menu_order":13,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-71","chapter","type-chapter","status-publish","hentry"],"part":37,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/71","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/users\/90"}],"version-history":[{"count":3,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/71\/revisions"}],"predecessor-version":[{"id":345,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/71\/revisions\/345"}],"part":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/parts\/37"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/71\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/media?parent=71"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapter-type?post=71"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/contributor?post=71"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/license?post=71"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}