Basic Features of Foundation Fieldbus (FF)

Foundation fieldbus (FF) and Profibus are the two most universal serial data bus formats that are used for interfacing between the central processor and smart devices in the process control system.

The Foundation Fieldbus is mainly used in U.S. while Profibus format is primarily used in Europe.

A serial data bus is a single pair of twisted copper wires that allows communications between a central processing computer and multiple monitoring points and actuators where smart sensors are employed as illustrated in the figure below:

Figure 1(a) Foundation Fieldbus Connection

The bus system uses time division multiplexing. The serial data word from the central processor contains the address of the peripheral unit being addressed in a given time slot and the data being sent. Foundation Fieldbus current from a constant current supply is digitally modulated. The information on the Foundation Fieldbus is provided in ISA 50.02 standards.

The comparison of characteristics of serial data buses is presented in table 1 below:

The original Foundation Fieldbus was designated H1, a new generation of the H1 is the HSE, which use Ethernet LAN to provide operation under the TCP/IP protocol employed for the Internet. The Foundation Fieldbus HSE offers advantages like increased speed, unlimited addresses, and standardization.

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You can also read: Types of Sensors used in Measurement and Process Control

Contents

1 Advantages of Serial data bus formats
2 Shortcoming of Serial data bus

Advantages of Serial data bus formats

Higher accuracies are achieved compared to analog signal transmission.
They system replaces all the leads to all the monitoring points by one pair of leads.
New units can be added to the bus with no extra wiring; a plug and play feature is provided giving faster control and programming is the same for all systems.
It provides more powerful diagnostics.

Shortcoming of Serial data bus

Failure of the bus, such as broken wire can shut the whole process down, whereas with the direct connection method only one sensor is disabled. Nevertheless, this weakness can be overcome by employing a redundant or backup bus in parallel to the first bus, so that if one bus malfunctions, the backup can be used.

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John Mulindi

John Mulindi is an Industrial Instrumentation and Control Professional with a wide range of experience in electrical and electronics, process measurement, control systems and automation. In free time he spends time reading, taking adventure walks and watching football.