IM01-Industrial communications
Unit 1Introduction to industrial communications

Why do we need communications?

A complex automated system needs to decentralize its control, otherwise, it has complete control in a single cabinet brings too large wiring.

A decentralized control is called distributed control, but then we need to know the different controls, that is to say, what others are doing by just synchronizing the machines.

It has the following advantages:

  • Simple programming.
  • Cost reduction of wiring costs (less time and less bugs)
  • Simple extensions and less expensive
  • Simple modifications
  • Efficient management errors
  • Monitoring of the integrated transmission system communications
  • Simple maintenance

TO KNOW MORE
If you want to learn more, you can check the following information about this. This is from Siemens, a great company which develops a lot of information about communications.
/ SIMATIC PCS 7
  1. Types of nets of communications
  2. Setting bus

The basic distribution is about one cable segment to which the devices are connected.

The mode of transmission is random, a computer transmits when needed. If there are simultaneous transmissions (collisions), special algorithms solve the problem.

Among the highlights are the following:

  • High speed transmission.
  • Falling equipment does not affect the rest of the network.
  • Communication is bidirectional ( all computers can transmit as needed )
  • Easy expansion.

1.22 - Setting Ring

The transmission medium form is a closed loop (ring) to which the equipment is connected.

It is based on a series of point-to- point to the next station.

The mode of transmission is organized in turns by passing a permit transmission from one station to another (baton pass or token passing).

In such networks using optical fibre (security features to implement redundant power rings) is widespread.

The most important features of this topology are:

  • Master-slave system.
  • Fixed transmission time.
  • The fall of a computer does not affect the rest.

1.3Configuration star

In this configuration, all computers are connected to a computer or hub that performs the functions of control and coordination (Host).

The main features are:

  • Easy maintenance.
  • The core team, the Host, controls the entire network.
  • The network performance (speed) depends on the Host.
  • The fall of a computer does not affect the rest.
  • If the Host stops, the network also stops.

1.4Setup tree

Mix the characteristics of the star and the line.

It is in bus systems sensor-actuator type (AS-i)

1.5Setup network

It allows connection between two stations through multiple paths.

The main features are:

  • Reliability and fault tolerance. The fall of a transmission line is solved by redirecting traffic the other way.
  • High cost of implementation.
  • Not used in field buses.

HIGHLIGHTS
The distribution system communications depends on the type of cable used and the type of network you want to implement.
  1. Relations between net elements
  2. MASTER-SLAVE

When planning communications, there is usually a hierarchy between the teams in which one is in control of communications (temporary or permanent) is established. It is what is known as master-slave relationship.In the industrial environment, the Master is a robot that can read or write about the slaves of controlling network, while the slave receives the messages sent by the master and issues when it comes to order to do so.

Slaves In two categories:

  • Slaves Assets: They are teams with a PLC that receive commands and execute their own program.
  • Slaves liabilities: They act as dumb terminals, not running any program and performing the function of Input-Output Master remote controller.

An example of a network with master-slave relationship could be a network of Profibus-DP (Siemens) or Festo Fieldbus protocol (Festo)

2.22 – CLIENT-SERVER

Another type of communication is based on the provision of services by

some partners in a network, and the use of these services by the rest. Relations are called client-server type.

A client is a computer network that requests services to a station. The Server is a station that provides those services requested.

A server can be a slave to your network.

A station may be, in turn, Customer and Server.

An example of a network with client-relations could be a network server to MPI or Profibus-FDL protocol (Siemens)

2.33 - PASS TOKEN (TOKEN BUS) (VARIOUS MASTER)

Active bus stations connected to PROFIBUS form a logical token-passing ring in ascending numerical order by addresses PROFIBUS. This logical order is independent of the physical layout of the stations.

The witness confers the right to transmit information over the network. This witness is relayed between stations in the active bus through a telegram special witness. When a station has the token, it can send telegrams called the duration of the retention time of the control (configuration). Once it is passed the station can only send a high priority message. If a station has no message to send, it directly passes the token to the next station in the logical ring. This active station except with the existing highest address on the bus is also called HSA (Highest Station Address). The station is the only witness to the bus station with active low address bus, so that the ring closure steps softtoken again. This access method is independent of the physical network used PROFIBUS.

  1. Types of field bus
  2. Field bus MPI

The MPI bus is a field bus communication developed by Siemens and included as standard in their CPU. It was initially developed as a programming interface. It also serves as a means of communication between components working as a man / machine interface and as a means of communication between automation devices.

One of its main features is its ease of configuration and commissioning underway.

The significant disadvantage to PROFIBUS is that the transmission protocol SIEMENS is Standard, which means that no product other than SIEMENS can be embedded into this type of bus.

It allows simultaneously connect to other programming elements such systems such as HMI (Operator Panels / Workstation), S7-300, M7-300, S7-400 and M7-400.

3.2PROFIBUS

It used for complex networks composed of elements. It allows connection of decentralized digital systems and single and multi master protocols astoken passing method and Master – Slave. It is based on DIN 19245, which provides use in field levels.The protocol fits the application level (PROFIBUS -DP I / S Distributed ). It allows up to 127 stations.

Average amounts of data (up to 240 bytes). The speed is from 9.6 Kbit / s to 12Mbit /s.Up to 100km, depending on the type of transmission used.

3.3AS -I

AS- I (Actuator Sensor Interface ) is applied to the lowest level .

It intended to replace conventional wiring of a machine by a pair of wires that can transmit data from different sensors and actuators.

It replaces all wiring cables, cabinets and specific connection terminals.

You can connect up to 248 binary input and 186 output signals via a single cable.

Power and data are on the same cable.

Ability to transmit analogue signals.

Maximum cycle time of 5ms .

Up to 100m in length in a single cable.

Operation as master-slave.

No need specialized personnel for installation.

3.4CAN Bus

The system CAN bus (Controller Area Network) was originally developed by Bosch in cooperation with Intel, to reduce wiring Automobile industry.

Its main features are:

  • Reduce costs.
  • Robust and safe
  • Efficiency and ease of data management
  • Facing control sensors and actuators.

3.5Industrial Ethernet

At the management level it is responsible for connecting large automation systems. The most common form of mapping Ethernet is the star, where one signal concentrator (Hub) distributes it to different places at once. Among Hub distribution there is also star.

Its main features are:

  • Large volumes of data and large distances.
  • Up to 100Mbit / s (Fast Ethernet)
  • Random access to the bus (CSMA / CD)
  • Over 1,000 stations.
  • 1500m in Electrical and 200km fibre optic network.
  1. Standards of communications

In a series transmission voltage levels are used to determine the characteristics of the communication. PC, useRS232 standard, updated to the USB port. PLC use RS485 communication standard for MPI communications and RS422 communications for PPI (a point to point interface). The different communications standards require us to use the PC to PLC adapters.

4.1RS232

Not used in industrial field buses, it has been the standard used in computer communications until recently it has been replaced by the USB connector. The RS- 232 interface is designed for short distances up to 15 meters as standard, and low communication speeds of no more than 20 Kilobits / second. However, it is often used at higher speeds with an acceptable result. The interface can work in asynchronous or synchronous communication channel and types of simplex, half duplex or full duplex. In a simplex channel data is always travelling in one direction, for example from DCE to DTE. In a half duplex channel , data can travel in either direction , but only for a certain period of time ; then the line should be switched before the data can travel in the other direction . In a full duplex channel, data can travel in both directions simultaneously. Handshaking lines of the RS- 232 is used to solve the problems associated with this mode of operation, as in what direction the data must travel at a given instant.

4.2RS 485

Is the most widespread hardware configuration for fieldbuses.

Key features are:

  • Up to 32 stations
  • Matching resistors in extreme
  • Speed ​​range spanning 9.6KBit/s to 12MBit / s
  • Shielded twisted pair cable.
  • According speed up to 1200m transmission distance.
  • Good immunity to interference signals since this voltage difference.
  • Allows multipoint connections: Red MPI
  • Range of bus-7V to +12 V

4.3RS422

It does not allow bus applications (it is point to point) PPI

4.4Comparative of standards

CHARACTERISTIC / RS 232C / RS 422A / RS485
Mode of work / One wire / Differential / Differential
Number of emissary and receptors / 1 emissary
1 receptor / 1 emissary
10 receptors / 32 emissaries
32 receptors
Speed of transmission Bits/s / 20K / 10M / 10M
Voltage in common mode / ± 25V / + 6V
-0.25V / +12 V
-7V
Voltage out emissary / ± 5 Vmin ±15Vmax / ±2Vmin / ± 1,5 Vmin
Emissary load / 3KΩ - 7KΩ / 100 Ω min / 60 Ω min
Wire length / 15 m / 1200m / 1200m
/ Video about Industrial communications

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IM01-Industrial communications/ Unit 1