A bus terminal is an advanced terminal block that can process different analog and digital input and output signals. It is housed and wired in a simple and compact way like a conventional terminal block, but unlike the terminal block, it has intelligent electronics. In control cabinets and terminal boxes, bus terminals with bus couplers such as EtherCAT or SERCOS are increasingly being used.
Construction of Bus Terminal
A bus terminal unit usually consists of a bus coupler and a larger number of electronic terminal blocks. The bus coupler has an interface to a fieldbus and thus integrates the bus terminals into the control system. Bus couplers with their own intelligence are called bus terminal controllers. They already have PLC functionality on a small scale and can handle smaller control tasks decentrally, without the intervention of the control computer.
Communication between the bus coupler and the individual bus terminals usually takes place via an internal terminal bus. The connection between the bus terminals is made wirelessly via contacts.
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A bus terminal unit is mounted in a control cabinet on a DIN rail. State-of-the-art systems allow the arbitrary arrangement of bus terminals of various signal types. The replacement of individual bus terminals or the subsequent expansion of the bus terminal unit is also possible with these systems within the limits of system physics. Usually, bus terminals are plugged together sorted by signal type, which benefits the clarity in a control cabinet.
Application of Bus Terminal
Bus terminals are used wherever analog and digital inputs and outputs (I/Os) are to be wired and transmitted to a controller via a fieldbus. The main task is to bundle the large number of different signals, e.g. on one machine, and to forward them to the controller via a uniform bus signal or to pass on commands from the controller to the actuators. By using master terminals within a bus terminal string, it is possible to transfer signals from sub-levels that communicate with each other via another fieldbus signal to the higher-level fieldbus. In addition, special terminals make it possible to control drives directly from the terminal network.
Originally, the bus terminal was developed for industrial automation technology. Their main area of application is mechanical and plant engineering. Due to the ongoing development in the field of building automation, bus terminals are now also used in the automation of buildings. In the meantime, special terminals have been developed for this area, which are designed to meet the special requirements of building automation. These include, for example, dimmer terminals for controlling lighting equipment, triac terminals for controlling blind motors, and communication or master terminals that integrate the bus systems commonly used in building technology into the higher-level bus system.
