Progress does not stand still. Therefore, there are more and more new devices. Some of them are a significant modification of previously developed devices. These include programmable controllers. What are they and where are they used?
What is called a programmable controller
This is the name of a microprocessor device that collects, converts, processes and stores information. Based on it, it can send control commands. Physically, this device is limited to a finite number of inputs and outputs. Sensors, keys,
actuators are connected to them
. Programmable controllers are aimed at real-time operation. How did they create them?
How it all began
Industrial automation began with contact relay circuits that controlled the ongoing processes. They had a fixed logic of work, and when changing the algorithm had to redo everything. But over time, inconvenience led to a gradual improvement of the design and programmable logic controllers arose.
Principle of operation
What is the basis of their functioning? It should be noted that programmable controllers are quite different from other microprocessor devices. So, the software component consists of two parts:
- System support. This is a kind of operating system that controls the operation of nodes, links components and conducts internal diagnostics.
- The software part that deals with the management and implementation of all functions. So, it is entrusted with the tasks of polling inputs, executing a user program, setting output values, as well as some auxiliary operations (visualization, preparation for sending data to the debugger).
The reaction time for each event depends on the time that is spent on executing one cycle of the application program. The more powerful components are used, the less it will be.
Programmable Controller Response
Freely programmable controllers have memory, which depends on the history of events. And based on what has already happened, they can react differently to what is happening now. Programmable controllers differ from simple combinational machines in that they can be time-controlled, have advanced computing abilities, and can perform digital signal processing.
Inputs and outputs
They are of three types: analog, discrete and special. In the first type, an electrical signal reflects the presence of a certain physical quantity at the current instant of time, which is done using a current or voltage level. So, they can transmit data about temperature, weight, position, pressure, frequency, speed and other similar information. Almost always they are multi-channel. Discrete inputs can work with one binary electric signal. It can be described in two states - off or on. The digital inputs are usually designed to receive standard signals with a constant current level of approximately 10 mA at 24 V. Given the fact that programmable controllers are digital computers, it is necessary to make the appropriate conversions. The result is a discrete variable with a certain rank. As a rule, in one device they use 8-12 pieces. To control most technological processes at altitude, this is enough. In addition, with an increase in bit depth, the amount of industrial interference increases, which negatively affects the operation of other devices.