There are various communication networks designed to connect different industrial field devices and I/O modules. They are described based on certain protocols. A protocol is a set of rules used in communication between two or more devices. Based on these protocols, communication networks are classified into several categories. Some common and popular industry communication standards are described below
1. Serial Communication
The serial protocol is the basic communication system provided for all controllers such as PLCs. This protocol is implemented using standard protocols such as RS232, RS422 and RS485. The abbreviation RS stands for Recommended Standard – The proposed standard which defines the serial communication characteristics in terms of electrical, mechanical and practical features.
The serial communication interface is either integrated into the CPU or the processing module (in the Programmable Logic Controller) or it may be a separate communication module. These RS interfaces are mainly used to transmit data reasonably at a high data rate between the PLC and the remote device. Barcode readers, printers and vision systems are examples of these interfaces.
The RS-232 serial protocol is designed to support a transmitter and a receiver and thus it provides communication between a controller and a computer. Maximum cable length must be up to 50 feet. The serial communication standards RS 422 (1Tx, 10 Rx) and RS485 (32Tx, 32 Rx) are designed to communicate between a computer and multiple controllers. These standards are limited to lengths of 1650 feet (in the case of RS422) and 650 feet (in the case of RS485).
2. HART (Highway Addressable Remote Transducer)
HART is an open process control network protocol, superimposing digital communication signals on top of 4-20mA signals using the Bell 202 Frequency Shift Keying (FSK) technique.
It is the only communication network that facilitates both analog and two-way digital communication at the same time by the same wiring, and thus these networks are also called hybrid networks. This digital signal, called the HART signal, carries diagnostic information, device configuration, calibration and other additional process measurements.
HART network operates in point-to-point or multi-point mode. In point-to-point mode, 4-20 mA current signals are used to control the process while HART signals remain unaffected. HART multipoint network is used when devices are widely spaced. HART-compatible multivariable smart field devices are widely used in many industries. HART communication network is mainly used in SCADA applications.
3. DeviceNet
This is an open device hierarchy based on CAN technology. It is designed to interface field devices (such as sensors, switches, barcode readers, control panel displays, etc.) with higher level controllers (such as PLCs) with acceptance. unique basic CAN protocol. It can support up to 64 nodes and supports up to a total of 2048 devices.
It reduces network costs by integrating all devices on four-wire cables that carry both data and power. Power on the network allows devices to be powered directly from the system and thus reduces the physical connection points. This network is commonly used in the automotive and semiconductor industries.
4. ControlNet
It is an open control network that uses Common Industrial Protocol (CIP) to combine the function of peer-to-peer and I/O networks by providing high-speed performance. This network is a combination of Data Highway Plus (DH +) and remote I/O. It is used for real-time data transmission of time-critical and non-time-critical data between I/O or microprocessors on the same network.
It can communicate with up to 99 nodes at a data rate of 5 million bits per second. It is designed for use on both equipment and field levels of industrial automation systems. It provides media and media redundancy at all nodes of the network.
5. Modbus
It is an open system protocol that can run on many different physical layers. It is the most widely used protocol in industrial control applications. It is a serial communication technique that provides a master / slave relationship to communicate between devices connected on the network. It can be done on any transmission medium, but is often used with RS232 and RS485.
Modbus serial with RS232 or RS485 (as physical layers) facilitates connection of Modbus devices with controllers (such as PLCs) in the bus structure. It can communicate between a master and a number of slaves up to 247 with a data transfer rate of 19.2 kbits/s.
A newer version of Modbus TCP / IP uses Ethernet as a physical layer to facilitate data exchange between PLCs in different networks. Regardless of the physical network type, it facilitates the method of accessing and controlling one device by another device.
6. Profibus
Profibus is one of the widely known and widely implemented field networks. These networks are mainly used in process automation and factory automation fields. It is best suited for complex communication tasks and time-critical applications. There are three different versions of Profibus, Profibus-DP (Decentralized Periphery), Profibus-PA (Process Automation) and Profibus-FMS (Fieldbus Message Specification).
7. Foundation Fieldbus
It is an open fieldbus standard specifically designed to meet the mission-critical needs of a safe environment. It is a type of LAN for fieldbus compatible devices and controllers used in manufacturing and processing industries.
It is an open fieldbus standard specifically designed to meet the mission-critical needs of a safe environment. It is a type of LAN for fieldbus compatible devices and controllers used in manufacturing and processing industries.
This is a two-way digital protocol standard, defined by safety standard IEC 61158-2 (for FF H1) and compatible with Ethernet equipment (in the case of FF HSE). The three types of FF networks include low speed H1, high speed H2 and high speed Ethernet HSE.
- The H1 network supports a speed of 31.25 kbps.
- The H2 network supports 2 speeds of 1.0 Mbps and 2.5 Mbps.
- HSE network supports 10 or 100 Mbps speeds because it uses the Ethernet protocol.
