Industrial automation incorporates programmable logic controllers in the manufacturing process. Programmable logic controllers (PLCs) use a processing system which allows for variation of controls of inputs and outputs using simple programming. PLCs make use of programmable memory, storing instructions and functions like logic, sequencing, timing, counting, etc. Using a logic based language, a PLC can receive a variety of inputs and return a variety of logical outputs, the input devices being sensors and output devices being motors, valves, etc. PLCs are similar to computers, however, while computers are optimized for calculations, PLCs are optimized for control task and use in industrial environments. They are built so that only basic logic-based programming knowledge is needed and to handle vibrations, high temperatures, humidity and noise. The greatest advantage PLCs offer is their flexibility. With the same basic controllers, a PLC can operate a range of different control systems. PLCs make it unnecessary to rewire a system to change the control system. This flexibility leads to a cost-effective system for complex and varied control systems.
An early development of sequential control was relay logic, by which electrical relays engage electrical contacts which either start or interrupt power to a device. Relays were first used in telegraph networks before being developed for controlling other devices, such as when starting and stopping industrial-sized electric motors or opening and closing solenoid valves. Using relays for control purposes allowed event-driven control, where actions could be triggered out of sequence, in response to external events. These were more flexible in their response than the rigid single-sequence cam timers. More complicated examples involved maintaining safe sequences for devices such as swing bridge controls, where a lock bolt needed to be disengaged before the bridge could be moved, and the lock bolt could not be released until the safety gates had already been closed.
Par défaut, les navigateurs et leurs drivers doivent être disponibles sur la même machine que le serveur WebDriver (on verra plus tard dans cet article qu'il est possible de faire autrement). Mais grâce à l'architecture client-serveur, les machines peuvent être distantes (Remote WebDriver). Ce qui vous permet par exemple de continuer à manipuler votre serveur de développement pendant que des serveurs distants exécutent vos tests. Vous n'avez pas de blocage de votre interface graphique.
Si vous pensez aux tâches en ligne que vous réalisez, il y a probablement des actions qui viennent à l’esprit et pour lesquels le logiciel serait très utile pour mais qui ne serait simplement pas commercialisable ou rentable pour un développeur. Ces actions seraient trop spécifiques pour en justifier le développement d’un logiciel pour les executer.
I used Firebug to find the ID of the search button (magnifying glass) on the page, then used .getElementById again to grab it, and the .Click method to click it. Alternatively, we could have submitted the search box form like this instead objIE.document.getElementById("search_form_homepage").Submit. Actually, there’s a simpler method still that would allow us to skip the previous 3 steps altogether. Can you see it? Hint: take a look at the url we ended up with… https://duckduckgo.com/?q=auto+parts+in+Houston+TX. Got it? If you still don’t see it, and you don’t think you’ll be able to sleep tonight, email me 🙂