joji books

Tag: PLC

  • PLC Communication Services

    A PLC system with communication interfacing capabilities is configured using several networked components, such as PLCs, a computer, communication modules, and HMI. These components can exchange data between two or more communication partners through the network using specific protocols for handling the data traffic.

    A network is characterized by the type of hardware involved, the communication procedure, and the data transfer rate. Accordingly, PLC communication networks are multi-point interface (MPI), Profibus, Industrial Ethernet, and point-to-point (PTP) connections.

    Multi-Point Interface (MPI)

    Multi-point interface (MPI), used in SIEMENS PLC systems, is designed as a programming device interface and is intended for networking a small number of CPUs to exchange small volumes of data.

    PROFIBUS

    Profibus complies with the standard EN 50170 and is used for networking field devices for communication. This type of connection is a local area network that provides a high-speed data communication bus to which devices within the local area can be connected.

    Industrial Ethernet

    Industrial Ethernet is a network for connecting PLCs and computers. It is suitable for the high-speed exchange of large quantities of data and facilitates communication between the communication partners.

    Point-to-point (PTP) Connection

    In a point-to-point connection, a communications processor forms the interface between a PLC and a communications partner. Serial communication occurs when bits belonging to each byte of information are transmitted one after the other in a serial order.

    Programmable Logic Controllers and Programming Concepts


    With Electrical, Pneumatic, and Hydraulic Applications

    Joji Parambath

    Cables

    Cables are used as the transmission medium for communication among devices connected in a PLC system. There are two types of cables available. They are: (1) Copper cables and (2) Fibre-optic cables.

    • Copper cable can be sub-divided into: (1) 2-core cable, (2) coaxial cable, and (3) shielded twisted-pair cable
    • Fibre-optic cable can be sub-divided into: (1) glass fibre-optic cables and (2) plastic fibre-optic cables

    RS-232C

    RS-232C interface is a kind of serial physical interface standard. This method is based on 1:1 communication, which is generally applied to the point-to-point communication within a short distance of 15 meters.

    RS-485

    RS-485 is a network interface that uses a master-slave communication method. That is one master communicating with multiple slaves (1: N). This network can be used as a two-wire or four-wire network. RS-485 network supports long-distance links, and the cable length can be up to 1200 m.

    RS-422A

    RS-422A is a network interface that also uses a master-slave communication method. This network can be used as a two-wire or four-wire network. RS-422A network supports long-distance links, and the cable length can be up to 1200 m.

    Authored by

    Joji Parambath

    Author

    Fluid Power Educational Series

    If you are interested in a PLC course with pneumatic applications, we invite you to explore the comprehensive training program offered by Fluidsys Training Centre Pvt Ltd., Bangalore.

  • Proximity Sensor Circuit Technology

    Proximity Sensor Circuit Technology

    Discrete output proximity sensors are most important for industrial applications. They gain importance in such applications where it is necessary to record or count moving objects or work-pieces on machines or conveyors. Based on the way of connection of the final output amplifier transistor of a discrete proximity sensor to the power supply terminals, proximity sensors can be categorized into two types:

    • Sinking (NPN) output sensors
    • Sourcing (PNP) output sensors

    Sourcing (PNP) Output sensor

    The sourcing output sensor has a PNP transistor output with its emitter connected to the +Vcc of the supply for positive switching, as shown in Figure 1. The load is connected between the proximity sensor output and the negative potential. This connection means that the sensor output will be pulled up to the positive potential, and hence the grounded load will be connected to the positive potential through the transistor in the switched state. This connection will allow the current to flow from the positive potential through the sensor to the output (hence sourcing). This sensor is best selected when all electrical devices in the control system use a single source of the supply voltage.

    Figure 1 | A sourcing output proximity sensor and its load connection

    Discrete Sensor connection to PLC Input

    As discussed, the output of a discrete proximity sensor can be sinking or sourcing type. Similarly, a discrete PLC input can be sinking or sourcing type. Remember, it is important to interface a proximity sensor to the associated PLC input correctly for the proper operation of the PLC system. In general, a sourcing proximity sensor should be connected to a sinking PLC input, and a sinking proximity sensor should be connected to a sourcing PLC input to avoid the erratic operation of the system. For the sourcing sensor output, the PLC input circuit is wired with the common terminal connected to the common of the sensor, as shown in Figure 2.

    Figure 2 | A sourcing sensor output connected to a sinking PLC input

    Electro-pneumatics and Automation

    Joji Parambath

    This book explains the functioning of primary solenoid valves and various electrical control components. Many typical single-actuator and multiple-actuator electro-pneumatic circuits are also developed to illustrate various applications of electro-pneumatics.

    Joji Parambath

    Author

    Fluid Power Educational Series Books