It offers distinct advantages over traditional analog and discretewiring or even other digital buses — at lower total installed cost andlower ongoing costs.
FOUNDATION fieldbus is an all-digital, serial, two-way communications systemthat serves as the base-level network in a plant or factory automationenvironment.
Two related implementations of FOUNDATION fieldbus have beenintroduced to meet different needs within the process automationenvironment.• H1 works at 31.25 Kbit/sec and generally connects to fielddevices. It provides communication and power over standardtwisted-pair wiring. H1 is currently the most commonimplementation.• HSE (High-speed Ethernet) works at 100 Mbit/sec and generallyconnects input/output subsystems, host systems, linking devices,gateways, and field devices using standard Ethernet cabling. Itdoesnt currently provide power over the cable, although work isunder way to address this.
•Conventional analog and discrete field instruments use point-to-point wiring:one wire pair per device. As a digital bus, FOUNDATION fieldbus doesnt havethose limitations.•Multidrop wiring. FOUNDATION fieldbus will support up to 32 devices on asingle pair of wires (called a segment) -- more if repeaters are used. In actualpractice, considerations such as power, process modularity, and loop executionspeed make 4 to 16 devices per H1 segment more typical.•That means if you have 1000 devices -- which would require 1000 wire pairswith traditional technology -- you only need 60 to 250 wire pairs withFOUNDATION fieldbus.•Multivariable instruments. That same wire pair can handle multiple variablesfrom one field device. For example, one temperature transmitter mightcommunicate inputs from as many as eight sensors -- reducing both wiring andinstrument costs.
•Other benefits of reducing several devices to one can include fewer pipepenetrations (for improved safety and reduced risk of fugitive emissions) andlower engineering costs.•Two-way communication. Information flow can now be two-way. A valvecontroller can accept a control output from a host system or other source andsend back the actual valve position for more precise control.•New types of information. Traditional analog and discrete devices have noway to tell you if theyre operating correctly, or if the process informationtheyre sending is valid. But FOUNDATION fieldbus devices can tell you if theyreoperating correctly, and if the information theyre sending is good, bad, oruncertain.•Control in the field. FOUNDATION fieldbus also offers the option of executingsome or all control algorithms in field devices rather than a central hostsystem.
Savings in engineering & design 50%No additional cost in instrumentation 85%Savings in commissioning & startup 80%Reduced overall staff time 72%Reduced wiring cost 77%Achieved return in less than two years 75%
Enhanced device diagnostics 90%Enhanced process diagnostics 72%Reduction in unnecessary visit to field 72%ID problems before may happen 70%Tighter control of the plant 60%Enhanced effectiveness of system 61%Increased system availability 59%Ease of device replacement 59%
The Fieldbus Foundation is an independent, not-profitorganization based on the following principles:• Fieldbus technology is an enabling technology; not adifferentiating technology.• Fieldbus technology is open and available to all parties.• Fieldbus technology is based on the work of theInternational Electrotechnical Commission (IEC) andISA (the international society for measurement andcontrol).• Fieldbus Foundation members support and work withthe international and national standards committees.
Interoperability simply means that FOUNDATION fieldbusdevices and host systems can work together while giving youthe full functionality of each component.Host interoperability testing. Host systems undergo Foundation-supervised tests to demonstrate their support for specific interoperabilityfeatures.Interoperable isnt interchangeable. Interchangeable means you can freelysubstitute one device for another and still get exactly the same functionality.Interoperable, on the other hand, means different devices from differentmanufacturers can work together -- but individual devices can have differentfunctionality.
The Stack Conformance Test ensures that the deviceinterfaces correctly with the bus; that is, electricalcharacteristics and bus access are consistent with thefieldbus specification.The Device Interoperability Test ensures that thedevices function blocks will interact with other blockscorrectly, and will provide accurate information andmode behavior.
A systems reliability is only as good as the reliability of eachof its parts. So it makes sense that the fewer the parts, the higherthe potential reliability of the system. Fieldbus allows the control "system" to have fewer partsbecause control can now be done in the field. That is, control does not have to go through all the hostsystems terminations, input cards, controllers, output cards, andso on — each a potential failure point.