Progress does not stand still. Therefore, there are more and more new devices. Some of them are significant modifications of previously developed instruments. These include programmable controllers. What are they and where are they applied?
What is called a programmable controller
This is the designation of a microprocessor device that collects, converts, processes and stores information. Based on it, it can send control commands. Physically, this device is limited by a finite number of inputs and outputs. Sensors, keys, actuators are connected to them. Programmable controllers are designed to work in real time. How were they created?
How it all began
Industrial automation began with contact-relay circuits that controlled ongoing processes. They had a fixed logic of work, and when the algorithm changed, everything had to be redone. But over time, the inconvenience led to a gradual improvement in design and programmable logic controllers appeared.
Working principle
What is the basis of theirfunctioning? It should be noted that programmable controllers are quite different from other microprocessor devices. So, the program component consists of two parts:
- System software. This is a kind of operating system that controls the operation of the nodes, connects the components and conducts internal diagnostics.
- The software part that manages and performs all functions. So, it is responsible for polling inputs, executing a user program, setting output values, as well as some auxiliary operations (visualization, preparation for sending data to the debugger).
The response time to each event depends on the time it takes to execute one application program cycle. The more powerful ingredients are used, the smaller it will be.
PLC response
Freely programmable controllers have a memory that depends on the history of events. And based on what has already happened, they may react differently to what is happening now. Programmable controllers differ from simple combinational automata in that they can be controlled by time, have developed computing abilities and can perform digital signal processing.
Entries and exits
They come in three types: analog, discrete and special. In the first type, the electrical signal reflects the presence of a certain physical quantity at the current moment of time, whichdone with current or voltage level. So, they can transmit data about temperature, weight, position, pressure, frequency, speed and other similar information. Almost always they are multichannel. Digital inputs can work with one binary electrical signal. It can be described by two states - off or on. Digital inputs are typically sized to accept standard signals that have a DC current level of approximately 10mA at 24V. Given the fact that programmable controllers are digital computers, it is necessary to make appropriate transformations. The result is a discrete variable with a certain bit. As a rule, 8-12 pieces are used in one device. To manage at height most technological processes, this is enough. In addition, with an increase in the bit depth, the amount of industrial interference increases, which negatively affects the operation of other devices.
