Tag: Industrial automation
-
Key Requirements for Industrial Control Computers
A computer is often used as part of a control system. The input data is typically from the operator’s commands and signals from the plant (flows, pressure, temperatures, limit switches, etc.). The output data comes in form of control actions to the plant and status displays to the operator. The instructions fed into the computer…
-
A Basic Introduction to Ladder Diagrams for PLC Programming
The ladder diagram which is a special type of wiring diagram consists of two power rails, which are placed vertically on each side of the diagram, and rungs, which are placed horizontally between the power rails. The power rails are the source of power in the circuit (ac or dc), where the left rail is…
-
Centralised vs. Decentralised Control Systems
Centralised control is usually carried out via computer software, having as inputs all the available sensors and producing signals for all the available actuators in the system. This control strategy is the most powerful, at least in theory, capable of extracting “optimal” performance. However, in practice, it requires non-standard apparatus (industrial computer data acquisition cards,…
-
Actuators as Automation Components
An actuator is normally controlled by the controller. The actuator, in turn, changes the output of an automated process. The actuator in an automated process may in actual fact be several actuators, each of which provides an output that drives another in the series of actuators. Let’s consider the hydraulic actuator that controls the position…
-
The Performance Limits for PID Controllers
PID Controllers can be applied successfully to most control problems in process control, electrical drive systems and servo mechanisms due to the fact that most of these processes have a dynamic behaviour that can be adequately approximated by a second-order process. However, the PID controller is not enough to control processes with additional complexities like…
-
How Modbus is used in Industrial Networks
Modbus is an open standardized communication protocol that was founded by Modicon. Initially it was designed for the communication among PLCs in industrial applications but it also gained significance use in building automation domain for instance in HVAC systems, DDCs and room control. In a nutshell, Modbus is an application layer messaging, protocol placed at…
-
Network Access Control Techniques
Access control methods are required in a network to ensure that only one user of the network is able to transmit at any one time. In ring-based local area networks (LANs), two commonly employed techniques are: Token Passing In this technique, a token i.e. a special bit pattern, is circulated. When a station wishes to…
-
Analog vs. Digital Controllers
Analog signals pass continuously through a full range of values for example a measuring device converts the process variable (PV), say temperature, into a signal corresponding to this temperature. Each temperature value corresponds to a value of the electrical signal. Digital signals belong to the group of discrete signals; here the individual signals are represented…
-
Position Control System using a Microprocessor-Based Controller
Consider the following figure illustrating a position control system employing a microprocessor-based controller with parallel ports: The system above has one output port and three input ports (each port has its own address). The output port is partitioned: Six bits are converted in a Digital Analog Converter (DAC) to provide the analog motor-drive signal, the…