The total number of relays, cam timers and drum sequencers can number into the hundreds or even thousands in some factories. Early programming techniques and languages were needed to make such systems manageable, one of the first being ladder logic, where diagrams of the interconnected relays resembled the rungs of a ladder. Special computers called programmable logic controllers were later designed to replace these collections of hardware with a single, more easily re-programmed unit.
Relay logic was introduced with factory electrification, which underwent rapid adaption from 1900 though the 1920s. Central electric power stations were also undergoing rapid growth and operation of new high pressure boilers, steam turbines and electrical substations created a large demand for instruments and controls. Central control rooms became common in the 1920s, but as late as the early 1930s, most process control was on-off. Operators typically monitored charts drawn by recorders that plotted data from instruments. To make corrections, operators manually opened or closed valves or turned switches on or off. Control rooms also used color coded lights to send signals to workers in the plant to manually make certain changes.[25]
Tout d'abord, qu'est-ce que ZennoPoster ? Le programme ZennoPoster est un nouveau logiciel russe qui a été conçu par ZennoLab et a été développé spécialement pour les webmasters (en particulier les experts en référencement) ; y compris ceux qui sont vraiment dans des activités dynamiques sur Internet qui impliquent de travailler dans divers domaines de l'optimisation pour les moteurs de recherche (SEO). ZennoPoster peut également être utilisé facilement par ceux qui ont des connaissances de base en programmation et est fortement recommandé pour le répertoire de n'importe quel programmeur professionnel. Donc, si vous pensez que vous êtes l'une de ces personnes, lisez ce qui suit.
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