The control of a long and complex process is divided into several levels of automation. The system architecture is oriented to the performance of different teams and facilitates the management of all thanks to a timely and clearly defined allocation of tasks and defined interfaces for exchanging data.
From now on, try the different levels of automation in an industrial plant, describing the functions to be performed on the network and the computers that comprise it, as well as the definition of some generic networks.
BE FIELD BUS (Fieldbus)
Often hear of "fieldbus" (field bus) is akin to "a network with its own characteristics," which allows us to connect field devices in industrial plants located in order to converse among themselves.
To some extent yes, but not the definition that best fieldbus (fieldbus).
So ... How can we define fieldbus (fieldbus)?
First, it is necessary to define what field. The "field" is the area of production or manufacture, ie the area where the machines are located and transmitters, along with their sensors (level, pressure, temperature, etc.) and actuators (valves, solenoids, relays, lamps, among others).
FIELDBUS or fieldbus, refers to communication technologies and protocols used in automation and industrial process control. The task is fieldbus sensors and actuators communicate with intelligent systems such as PLCs and computers so that they can provide information that can travel information systems throughout the plant.
Figure 3.1 Actuators and sensors in an industrial process
The fieldbus must strictly comply with the requirements of modularity, security, flexibility, resistance to interference, ease of installation, maintenance and programming. In addition, a fieldbus should cover mainly two different applications:
- The sequential control machinery or factories where protection against the danger of explosion is not critical. It is characterized by short reaction times, high data rate and bus length of 300 meters.
- Process control, where protection against explosion hazards should be safe ntrínsicamente. You can have cycle times of 100 ms for control and can cover distances greater than 1 500 meters.
And what types of field buses are there?
There fieldbus "owners" and "open."
FIELD BUS OWNER
These are systems that are characterized by their restriction: the product components from one manufacturer, therefore, there is no compatibility with products from other manufacturers.
One of the main advantages of these fieldbus is closed or owners upon request with configuration and setup, since all components are derived from a single manufacturer and therefore standardized. The disadvantage is the dependence of the products and prices from a manufacturer.
OPEN FIELD BUS
The open field buses are the opposite. These are systems that facilitate communication between devices from different manufacturers without further adaptations. In short, users can use or develop products based on these open field buses at a reasonable cost and without much effort. A complete availability of tools and hardware and software components.
But let ...
A field bus must allow at least three things:
- Interconnectivity: the equipment of various manufacturers can be connected to the bus safely.
- Interoperability: the ability to connect various components from various manufacturers,
- Exchange: a manufacturer's equipment can be replaced with equivalent functionality for other manufacturers' equipment.
Interconnectivity is the common denominator. If interoperability can not be achieved, the same operation is limited fieldbus and fieldbus such an option becomes unhelpful. The ultimate goal is the exchange capacity. This can only be possible if the specifications are complete and have a proper system of testing and validation of equipment.
... We have defined a field bus and we know that ios haf of two types: open and closed, but WHY USE A FIELD BUS?
Selecting a fieldbus correctly for a given application can provide the user with many tangible and intangible benefits.
- Reduce the complexity of the control system in terms of hardware. Reduces the amount of control equipment, such as PLC, DCS, hardware, etc. This in turn reduces the need to install large control rooms for such equipment. Since the wiring is drastically reduced in the field, the number of mounting accessories also dramatically reduced. All this implies a direct and significant savings in costs.
- By reducing the hardware requirements also reduce installation time and labor requirements. MPLEMENTATION The physical site is much faster. In addition, fieldbus diagnostic functions identified any errors in the connections.
- Because it reduces the complexity of control system design stage (Engineering) develops in less time and therefore costs less. The need to design complicated control schemes and wiring is simplified significantly.
- The future modifications, updates or upgrades are easily implemented and at lower cost.
- Selecting a recognized, open and well established, the field team of plant can be interchangeable with other manufacturers' equipment without worrying about compatibility issues.
- The downtime and production losses are reduced because the diagnostic procedures and troubleshooting fieldbus system allow you to take action quickly.
... And what fieldbus options currently exist?
At present there are many options. Some manufacturers have developed systems based on available technology (such as RS-232 or MODBUS protocol) with the constraints. Other companies, however, have developed new and more powerful management standards that provide greater amounts of information faster than MODBUS. An example of them is PROFIBUS.
We can list those that are very popular. Some of them are completely defined field bus, others are only basic technologies. Some are proprietary systems and others are open architecture.
The following buses are considered obsolete field, with a good past, but without much future:
Modbus.
HART.
Data Highway.
Data Highway Plus.
Some systems with better performance:
Profibus DP.
Modbus Plus ..
FIPIO
SINEC.
Omron SYSMAC.
Profibus FMS.
Allen-Bradley Remote I / O.
DeviceNet.
AS-I.
FIP.
Smart distribuite System.
Figure 3.2 Example of Fieldbus
