What is Input/Output?
In the most basic definition, I/O stands for inputs and outputs. In industrial automation, inputs and outputs are associated with buttons, switches, and sensors. For example, a person would create an input signal by pressing a button. As a result, a light will come on, which is the output signal. As you can imagine, industrial equipment may have hundreds of input and output signals of varying complexity. A fieldbus I/O system can help group signals from instruments on a machine and monitor and control the entire industrial equipment.
Fieldbus systems provide:
- Processor communication
- Device communication
- Control and timing
- Data buffering
- Error detection
Traditional Discrete Wiring
The traditional method of connecting field devices to a monitoring unit is point-to-point wiring. With discrete wiring, you connect field devices to junction boxes in the control panel. This method of I/O wiring works for smaller, less complex devices. However, larger devices can have hundreds of I/O points, making it a labor-intensive project. Not only that, but it becomes increasingly difficult to keep track of which wires go where. As a result, human error increases. But the headaches don't stop there. Sometimes there are late I/O changes, which can mean redesigning drawings, dividing control systems, moving wires, or even building new cabinets.
From Discrete Wiring to Fieldbus I/O Systems
Fieldbus, on the other hand, consists of a series of networked field devices that communicate serially over a 31.25kHz bus. On a fieldbus system, devices can use a pair of wires to pass data between each other and the host control system. With fieldbus, your data is not limited to measured variables, but also includes diagnostic data, status information, and alarms.
If you're on the fence about integrating fieldbus into your equipment, consider the following advantages and disadvantages:
Fieldbus I/O Advantages:
Instruments connected to a single trunk cable
Less wiring More
Smaller cabinet footprint
Ability to transfer diagnostic data
Control can be performed in the field device, reducing the control system's workload
Measurement of variables is more accurate because it is not converted to a current loop
Fieldbus I/O Disadvantages:
Requires further training
Limitations of intrinsically safe applications Safety
Systems are not universally accepted
Devices need to be tested for interoperability with host systems
Additional design work required (segmented calculations, control system requires additional configuration data)