Industry at the current stage of its development can not exist without modern and reliable automation systems. Since the production processes in terms of the complexity of constantly go to the next level, of manual control, when program logic controllers GE, it becomes impossible. It is also necessary to consider the fact, that the automation system - it saves. Since staff costs (but it is also a greater risk of) It will mean greater, than spending on automation.
Even if you move away from the industry, today there is equipment in any building - from the office, finishing warehouse. Everywhere there is engineering systems with automatic control. Applied automation in numerous areas, but in all automation systems around the same principle - the same can be said about the structure. In this structure, the center is always in the programmable logic controller. It can be called the "brain" of the entire system.
The principle of operation of the controller - cyclic. Cycle Start - a scan of the inputs. These input signals are sent to, coming from the various devices and sensors. The next step - is the calculation of the output status. The cycle is completed, the controller completes the installation of each output in a certain, given state.
so, first reads the status of the inputs, further executes the user program, after recorded output status. In this case, the sequence of these steps mandatory. In other words, adjustment of input states are not noticed by the controller, when the program is executed. And then we gradually come to a very important parameter of the controller - this time the reaction. If the comparison with minimal period change input states it is more, series of events, resulting in the system, skipped controller.
We should not forget one more point - Sensor reaction to a change does not occur in the instant mode. Respectively, full time period control response - it's not only time controller response, and the reaction time but separately sensors.
There are systems hard and soft real-time.
- In the first case controller response must not be in excess of a predetermined time threshold,.
- In the second case, the reaction time may be extended. quality of management will decrease, but performance remains (hard real-time, she lost).
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