{"id":8234557,"date":"2026-10-24T17:26:17","date_gmt":"2026-10-24T17:26:17","guid":{"rendered":"https:\/\/scn.eu\/?post_type=scn_guide&#038;p=8234557"},"modified":"2026-10-24T17:29:28","modified_gmt":"2026-10-24T17:29:28","slug":"hvad-er-en-plc","status":"publish","type":"scn_guide","link":"https:\/\/scn.eu\/da\/guider\/hvad-er-en-plc\/","title":{"rendered":"Hvad er en PLC? S\u00e5dan virker den \u2013 og s\u00e5dan v\u00e6lger du"},"content":{"rendered":"<div class=\"scn-guide\">\n<h1>Hvad er en PLC? S\u00e5dan virker den \u2013 og s\u00e5dan v\u00e6lger du<\/h1>\n<p class=\"g-lead\">En PLC er en industricomputer, der l\u00e6ser sensorer, tr\u00e6ffer beslutninger efter et program og styrer motorer, ventiler og lamper \u2013 igen og igen, nogle f\u00e5 millisekunder ad gangen. Her forklarer vi, hvordan den virker, hvilke programmeringssprog der findes, og hvordan du v\u00e6lger system.<\/p>\n<div class=\"g-short\"><b class=\"t\">Kort svar<\/b><\/p>\n<ul>\n<li><b>PLC<\/b> \u2013 Programmable Logic Controller, en programmerbar styring bygget til at styre maskiner og processer d\u00f8gnet rundt.<\/li>\n<li><b>Programcyklussen<\/b> \u2013 PLC&#8217;en l\u00e6ser alle indgange, k\u00f8rer programmet, skriver alle udgange og begynder forfra. En cyklus tager ofte nogle f\u00e5 millisekunder.<\/li>\n<li><b>Programmeringssprog<\/b> \u2013 standarden IEC 61131-3 definerer LD, FBD, ST og SFC. Instruktionslisten IL er udfaset.<\/li>\n<li><b>Kompakt, modul\u00e6r eller decentral<\/b> \u2013 v\u00e6lg efter antal I\/O, behov for udvidelse og hvor spredt anl\u00e6gget er.<\/li>\n<li><b>V\u00e6lg ud fra helheden<\/b> \u2013 I\/O, kommunikation, software og det, dine teknikere allerede kan, ikke kun prisen p\u00e5 CPU&#8217;en.<\/li>\n<\/ul>\n<\/div>\n<h2>Hvad er en PLC?<\/h2>\n<p>PLC st\u00e5r for <i>Programmable Logic Controller<\/i>, p\u00e5 dansk ofte bare kaldet en styring eller et styresystem. De f\u00f8rste kom i slutningen af 1960&#8217;erne for at erstatte store rel\u00e6tavler i bilindustrien. I stedet for at tr\u00e6kke nye ledninger, n\u00e5r en maskine skulle \u00e6ndres, kunne man \u00e6ndre programmet.<\/p>\n<p>En PLC er bygget til industrien: den t\u00e5ler vibrationer, elektriske forstyrrelser og varme i tavlen, og den k\u00f8rer det samme program d\u00f8gnet rundt i mange \u00e5r. Et PLC-system best\u00e5r af:<\/p>\n<ul>\n<li><b>CPU<\/b> \u2013 processoren, der k\u00f8rer programmet og rummer hukommelsen.<\/li>\n<li><b>Indgange<\/b> \u2013 digitale (24 V DC fra trykknapper og sensorer) og analoge (4\u201320 mA, 0\u201310 V, temperatur).<\/li>\n<li><b>Udgange<\/b> \u2013 transistor- eller rel\u00e6udgange til ventiler, kontaktorer og lamper og analoge udgange til frekvensomformere og reguleringsventiler.<\/li>\n<li><b>Kommunikation<\/b> \u2013 feltbusser og industrielt Ethernet til operat\u00f8rpaneler, drev og overordnede systemer.<\/li>\n<li><b>Str\u00f8mforsyning<\/b> \u2013 oftest 24 V DC.<\/li>\n<\/ul>\n<h3>Hvor bruges PLC&#x27;er?<\/h3>\n<ul>\n<li><b>Produktion<\/b> \u2013 pakkemaskiner, transportb\u00e5nd, robotceller, presser og testudstyr.<\/li>\n<li><b>F\u00f8devarer og proces<\/b> \u2013 dosering, batchprocesser og reng\u00f8ringssekvenser, ofte programmeret i SFC.<\/li>\n<li><b>Vand og spildevand<\/b> \u2013 pumpestationer og renseanl\u00e6g med fjernoverv\u00e5gning via SCADA.<\/li>\n<li><b>Energi<\/b> \u2013 vindm\u00f8ller, solcelleparker, batterilagre og koblingsstationer.<\/li>\n<li><b>Jernbane og infrastruktur<\/b> \u2013 styring om bord p\u00e5 tog, ved sporet og i tunneler.<\/li>\n<li><b>Bygninger<\/b> \u2013 ventilation, varme og belysning i st\u00f8rre bygninger.<\/li>\n<\/ul>\n<h2>Hvordan virker en PLC? Programcyklussen<\/h2>\n<p>En PLC arbejder i en fast l\u00f8kke, programcyklussen (scan). F\u00f8rst l\u00e6ser den alle indgange og gemmer v\u00e6rdierne. Derefter k\u00f8res programmet fra start til slut med de gemte v\u00e6rdier. S\u00e5 skrives resultaterne til udgangene, og PLC&#8217;en tager sig af kommunikation og diagnose. Derefter begynder det hele forfra.<\/p>\n<figure><img loading=\"lazy\" src=\"https:\/\/scn.eu\/wp-content\/uploads\/2026\/10\/scn-guide-plc-f1-da.webp\" alt=\"PLC&#x27;ens programcyklus: l\u00e6s indgange, k\u00f8r programmet, skriv udgange, kommunikation og diagnose, og s\u00e5 forfra\" width=\"1520\" height=\"600\" loading=\"lazy\" decoding=\"async\"><figcaption>PLC&#8217;en gentager de samme fire trin igen og igen.<\/figcaption><\/figure>\n<p>Cyklustiden afh\u00e6nger af programmets st\u00f8rrelse og processorens hastighed. En watchdog-funktion stopper PLC&#8217;en og s\u00e6tter udgangene i en sikker tilstand, hvis cyklussen tager for lang tid. H\u00e6ndelser, der er hurtigere end cyklussen, som pulser fra en encoder, h\u00e5ndteres med interrupts eller hurtige t\u00e6llermoduler.<\/p>\n<p>Til kommunikation bruges feltbusser og industrielt Ethernet som PROFINET, EtherNet\/IP, Modbus TCP, EtherCAT og PROFIBUS. Mod IT-systemer og skyen bruges OPC UA og MQTT oftere og oftere.<\/p>\n<h2>Programmeringssprog efter IEC 61131-3<\/h2>\n<p>Standarden IEC 61131-3 beskriver f\u00e6lles programmeringssprog til PLC&#8217;er, s\u00e5 en tekniker kan finde sig til rette p\u00e5 tv\u00e6rs af fabrikater. De fleste projekter blander flere sprog.<\/p>\n<div class=\"g-tbl\">\n<table>\n<thead>\n<tr>\n<th>Sprog<\/th>\n<th>Type<\/th>\n<th>Velegnet til<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td class=\"n\">LD \u2013 Ladder Diagram<\/td>\n<td>Grafisk, ligner et rel\u00e6diagram<\/td>\n<td>Logik og forriglinger. Let for elektrikere at fejlfinde i.<\/td>\n<\/tr>\n<tr>\n<td class=\"n\">FBD \u2013 Function Block Diagram<\/td>\n<td>Grafisk, blokke der forbindes<\/td>\n<td>Regulering og analoge signaler, for eksempel PID.<\/td>\n<\/tr>\n<tr>\n<td class=\"n\">ST \u2013 Structured Text<\/td>\n<td>Tekstbaseret, ligner Pascal<\/td>\n<td>Beregninger, l\u00f8kker og datah\u00e5ndtering.<\/td>\n<\/tr>\n<tr>\n<td class=\"n\">SFC \u2013 Sequential Function Chart<\/td>\n<td>Grafisk, trin og overgange<\/td>\n<td>Sekvenser som maskincyklusser og batchprocesser.<\/td>\n<\/tr>\n<tr>\n<td class=\"n\">IL \u2013 Instruction List<\/td>\n<td>Tekstbaseret, ligner assembler<\/td>\n<td>Udfaset i tredje udgave (2013) og fjernet i fjerde (2025). Bruges i \u00e6ldre programmer.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"g-short\">\n<p style=\"margin:0\">I Siemens STEP 7 og TIA Portal hedder modstykkerne LAD, FBD, SCL og GRAPH. STL svarer nogenlunde til IL.<\/p>\n<\/div>\n<h2>Kompakt PLC, modul\u00e6r PLC eller decentral I\/O?<\/h2>\n<figure><img loading=\"lazy\" src=\"https:\/\/scn.eu\/wp-content\/uploads\/2026\/10\/scn-guide-plc-f2-da.webp\" alt=\"Tre m\u00e5der at bygge et PLC-system p\u00e5: kompakt enhed, modul\u00e6rt system p\u00e5 skinne og decentral I\/O via netv\u00e6rk\" width=\"1520\" height=\"460\" loading=\"lazy\" decoding=\"async\"><figcaption>Tre m\u00e5der at bygge et PLC-system p\u00e5.<\/figcaption><\/figure>\n<ul>\n<li><b>Kompakt PLC<\/b> \u2013 CPU, indgange og udgange i \u00e9n enhed, ofte med mulighed for udvidelse med nogle f\u00e5 moduler. Passer til mindre maskiner, pumpestationer og bygningsautomation.<\/li>\n<li><b>Modul\u00e6r PLC<\/b> \u2013 CPU, str\u00f8mforsyning og I\/O-moduler p\u00e5 DIN-skinne eller bagplan. Du v\u00e6lger pr\u00e6cis de moduler, du har brug for, og kan bygge ud. Passer til st\u00f8rre maskiner og processer.<\/li>\n<li><b>Decentral I\/O<\/b> \u2013 I\/O-stationer ude ved maskinen, forbundet til CPU&#8217;en via feltbus eller Ethernet. Sparer meget kabel og g\u00f8r det nemmere at bygge maskiner i moduler.<\/li>\n<\/ul>\n<h2>PLC, PC-baseret styring eller mikrocontroller?<\/h2>\n<div class=\"g-tbl\">\n<table>\n<thead>\n<tr>\n<th>L\u00f8sning<\/th>\n<th>Styrke<\/th>\n<th>Passer n\u00e5r<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td class=\"n\">PLC<\/td>\n<td>Robust, forudsigelig cyklustid, nem fejlfinding og lang levetid<\/td>\n<td>Maskiner og processer, der skal k\u00f8re i mange \u00e5r og vedligeholdes af teknikere<\/td>\n<\/tr>\n<tr>\n<td class=\"n\">PC-baseret styring<\/td>\n<td>Meget regnekraft. Styring, HMI, billedbehandling og database i samme computer<\/td>\n<td>Avanceret motion control og datatunge applikationer<\/td>\n<\/tr>\n<tr>\n<td class=\"n\">Mikrocontroller<\/td>\n<td>Lav pris pr. enhed i store serier<\/td>\n<td>Produkter i store m\u00e6ngder, hvor du selv konstruerer og certificerer elektronikken<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>En <b>sikkerheds-PLC<\/b> bruges til n\u00f8dstop, beskyttelsesafsk\u00e6rmninger og lysgardiner. Den har dobbelte kanaler og selvdiagnose og er certificeret til for eksempel SIL 3 efter IEC 61508 eller PL e efter EN ISO 13849-1. Sikre signaler kan g\u00e5 i samme netv\u00e6rk som \u00f8vrige data med protokoller som PROFIsafe og FSoE.<\/p>\n<h2>S\u00e5dan v\u00e6lger du PLC \u2013 fem faldgruber<\/h2>\n<ol class=\"g-pit\">\n<li><b>For lidt I\/O.<\/b> Maskiner vokser. Planl\u00e6g med 10\u201320 procent reserve og plads til flere moduler.<\/li>\n<li><b>Kommunikationen bliver glemt.<\/b> Kontroll\u00e9r, hvilke protokoller frekvensomformere, paneler og andre maskiner bruger, f\u00f8r du v\u00e6lger CPU.<\/li>\n<li><b>Softwaren regnes ikke med.<\/b> Licenser og uddannelse kan koste mere end hardwaren. Kontroll\u00e9r, hvad der er inkluderet, og hvad opgraderinger koster.<\/li>\n<li><b>Man ser bort fra, hvad teknikerne kan.<\/b> V\u00e6lg et milj\u00f8, som dem, der skal fejlfinde klokken tre om natten, kender. Det kan betyde et system, der programmeres med de samme v\u00e6rkt\u00f8jer som eksisterende anl\u00e6g.<\/li>\n<li><b>Milj\u00f8et undervurderes.<\/b> Almindelige PLC-systemer er ofte specificeret til 0\u201360 \u00b0C. Tog, udend\u00f8rs skabe og mobile applikationer kr\u00e6ver et bredere temperaturomr\u00e5de, og tog desuden EN 50155.<\/li>\n<\/ol>\n<h2>PLC-systemer hos SCN<\/h2>\n<p>Vi har PLC-systemer fra Yaskawa (tidligere VIPA) i familierne Micro PLC, SLIO og 300S+. De kan programmeres i Siemens SIMATIC Manager (STEP 7) eller TIA Portal, og SLIO og Micro PLC ogs\u00e5 i Yaskawas Speed 7 Studio. Derudover har vi CODESYS-styringer fra Weintek og programmerbare controllere og remote I\/O fra Moxa.<\/p>\n<h3>Eksempler fra vores sortiment<\/h3>\n<div class=\"g-prod\"><a class=\"g-pc\" href=\"https:\/\/scn.eu\/da\/vare\/m13-ccf0000-da\/\"><img loading=\"lazy\" src=\"https:\/\/scn.eu\/wp-content\/uploads\/2025\/01\/M13-CCF0000.jpg\" alt=\"Yaskawa M13-CCF0001\" width=\"800\" height=\"800\" loading=\"lazy\" decoding=\"async\"><span class=\"g-pb\">Yaskawa<\/span><span class=\"g-pn\">M13-CCF0001<\/span><span class=\"g-pw\">Kompakt PLC med 16 DI, 12 DO, 2 AI og 2 PWM indbygget. Programmeres i Speed 7 Studio, SIMATIC Manager eller TIA Portal.<\/span><\/a><a class=\"g-pc\" href=\"https:\/\/scn.eu\/da\/vare\/cmt-ctrl01-da\/\"><img loading=\"lazy\" src=\"https:\/\/scn.eu\/wp-content\/uploads\/2025\/01\/cmt-ctrl01.png\" alt=\"Weintek cMT-CTRL01 CODESYS PLC og IIoT-gateway\" width=\"800\" height=\"800\" loading=\"lazy\" decoding=\"async\"><span class=\"g-pb\">Weintek<\/span><span class=\"g-pn\">cMT-CTRL01 CODESYS PLC og IIoT-gateway<\/span><span class=\"g-pw\">CODESYS-PLC og IIoT-gateway i \u00e9n \u2013 sender data via MQTT eller OPC UA.<\/span><\/a><a class=\"g-pc\" href=\"https:\/\/scn.eu\/da\/vare\/iologik-e1200-da\/\"><img loading=\"lazy\" src=\"https:\/\/scn.eu\/wp-content\/uploads\/2026\/10\/moxa-iologik-e1200-main.webp\" alt=\"Moxa ioLogik E1200 Ethernet remote I\/O-moduler\" width=\"800\" height=\"800\" loading=\"lazy\" decoding=\"async\"><span class=\"g-pb\">Moxa<\/span><span class=\"g-pn\">ioLogik E1200 Ethernet remote I\/O-moduler<\/span><span class=\"g-pw\">Ethernet remote I\/O med Modbus TCP og EtherNet\/IP og to porte til daisy-chain.<\/span><\/a><\/div>\n<div class=\"g-links\"><a href=\"https:\/\/scn.eu\/da\/vare-kategori\/produkter\/control-systems-da\/plc-systems-da\/\">PLC-systemer<\/a><a href=\"https:\/\/scn.eu\/da\/vare-kategori\/produkter\/control-systems-da\/plc-systems-da\/micro-plc-da\/\">Micro PLC<\/a><a href=\"https:\/\/scn.eu\/da\/vare-kategori\/produkter\/control-systems-da\/plc-systems-da\/slio-da\/\">SLIO<\/a><a href=\"https:\/\/scn.eu\/da\/vare-kategori\/produkter\/control-systems-da\/plc-systems-da\/300s-da\/\">300S+<\/a><a href=\"https:\/\/scn.eu\/da\/vare-kategori\/produkter\/control-systems-da\/gateways-da\/\">Gateways<\/a><\/div>\n<div class=\"g-cta\">\n<p>Skal du bygge nyt eller udskifte et \u00e6ldre styresystem? Sp\u00f8rg en af vores ingeni\u00f8rer \u2013 du f\u00e5r svar inden for 24 timer.<\/p>\n<p><a href=\"https:\/\/scn.eu\/da\/kontakt\/\">Sp\u00f8rg en ingeni\u00f8r<\/a><\/div>\n<h2>Ofte stillede sp\u00f8rgsm\u00e5l<\/h2>\n<details>\n<summary>Hvad st\u00e5r PLC for?<\/summary>\n<p>Programmable Logic Controller, en programmerbar styring. P\u00e5 dansk siger man ofte styring, styresystem eller bare PLC.<\/p>\n<\/details>\n<details>\n<summary>Hvilket PLC-sprog er mest udbredt?<\/summary>\n<p>Ladder (LD) er stadig almindeligt til logik, mens Structured Text (ST) bruges mere og mere til beregninger og st\u00f8rre programmer. De fleste projekter blander sprog.<\/p>\n<\/details>\n<details>\n<summary>Hvad er forskellen p\u00e5 PLC og DCS?<\/summary>\n<p>Et DCS (Distributed Control System) er et styresystem til store procesanl\u00e6g, hvor styring, operat\u00f8rbilleder og databaser er integreret fra starten. En PLC er mere selvst\u00e6ndig og mest udbredt i maskiner og mindre anl\u00e6g.<\/p>\n<\/details>\n<details>\n<summary>Kan jeg bruge en anden PLC end Siemens i et Siemens-milj\u00f8?<\/summary>\n<p>Ja. Der findes S7-kompatible PLC-systemer, for eksempel fra Yaskawa, der programmeres i SIMATIC Manager eller TIA Portal. Kontroll\u00e9r, hvilke funktioner og moduler der underst\u00f8ttes.<\/p>\n<\/details>\n<details>\n<summary>Hvad er en soft-PLC?<\/summary>\n<p>En PLC, der k\u00f8rer som software p\u00e5 en industri-PC i stedet for p\u00e5 sin egen PLC-hardware. Den giver mere regnekraft, men kr\u00e6ver en computer, der er bygget til industrimilj\u00f8.<\/p>\n<\/details>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>En PLC er en industricomputer, der l\u00e6ser sensorer, tr\u00e6ffer beslutninger efter et program og styrer motorer, ventiler og lamper \u2013 igen og igen, nogle f\u00e5 millisekunder ad gangen. Her forklarer vi, hvordan den virker, hvilke programmeringssprog der findes, og hvordan du v\u00e6lger system.<\/p>\n","protected":false},"author":11,"featured_media":8234364,"template":"","meta":{"_yoast_wpseo_focuskw":"hvad er en plc","_yoast_wpseo_metadesc":"Hvad er en PLC? L\u00e6r, hvordan en styring virker, programcyklussen, sprogene i IEC 61131-3, og hvordan du v\u00e6lger mellem kompakt, modul\u00e6r og decentral PLC.","_kad_post_transparent":"","_kad_post_title":"hide","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"hide","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","_scn_guide_cats":[670,882,896,884],"_scn_guide_sectors":[1011],"_scn_guide_type":"tech","_scn_guide_order":14,"footnotes":""},"class_list":["post-8234557","scn_guide","type-scn_guide","status-publish","has-post-thumbnail","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Hvad er en PLC? S\u00e5dan virker den \u2013 og s\u00e5dan v\u00e6lger du | SCN<\/title>\n<meta name=\"description\" content=\"Hvad er en PLC? 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