Читать книгу Control of Mechatronic Systems - Patrick O. J. Kaltjob - Страница 20

Data acquisition and transmission units are used: (i) to interface with various control devices (e.g. operator panel, detecting and measuring field devices); (ii) to transport process data between network nodes; (iii) to integrate process data from different sources on a single platform; and (iv) to integrate control functions (e.g. machine control and process control). These units operate through data transfer platforms and their data distribution service protocols. They can be designed based on the Open Systems Interconnection model, which is summarized as:

1 the physical layer, being either wired or wireless connection, such as twisted-pair wiring, fiber-optic cable or radio link, and the commutation unit connecting the network to the devices (e.g. field buses for data transfer between primary controllers and field control devices);

2 the network, transmission, and transport layers performing functions such as data routing over the network, data flow control, packet segmentation and desegmentation, error control and clock synchronization. In addition, these layers provide mechanisms for packet tracking and the retransmission of failed packets; and

3 the session and presentation layers mainly used for data formatting.