FOUNDATION Fieldbus features intrinsic safety, long wiring run length, and delivery of blocks of data over a two-wire system. In intrinsically safe applications, only 83mA of power are available for each segment, so it is important that field devices consume very little power. TopWorx FF products consume less than 17mA of power, so up to five devices can be used on each segment.

FOUNDATION Fieldbus is the ideal digital replacement for the traditional 4-20mA analog standard. Although it is tailor-made for analog instruments, such as control valves and transmitters, it is often appropriate for on/off valves as well. For example, in continuous processes (low discrete population), it is often logical to tie the on/off valves into the FF system rather than use conventional wiring or a completely different bus network for a small number of valves. And in batch operations (high discrete population) that are intrinsically safe, FF is often the only logical choice for networking on/off valves. TopWorx has recognized these issues and has created several cost-effective ways to extend the benefits of FF to on/off valves and other discrete devices.

FOUNDATION Fieldbus Network Highlights

Type of Network	Process Control Network
Physical Media	Twisted pair, fiber
Network Topology	Star, Bus
Maximum Devices	32 nodes/segment (16 nodes/segment on some Host systems)
Maximum Devices using Intrinsically Safe wiring	4-6 per repeated segment depending on power requirements of devices and the type of I.S. barrier used.
Maximum Distance
Maximum Distance	1,900 meters
Maximum Distance with repeaters (max. of 4 repeaters can be used)	9,500 meters
Communication Methods	Client/server, Publisher/subscriber, Event
	Both scheduled and onscheduled communications
Primary usage	Used for analog and discrete process control devices
Power and Communications on same twisted pair	Requires FF power supply (conditioner) to protect the digital communications
Device Power Supply	Can be supplied from bus (typical)
Wiring Types
Type A:	(Recommend using Type A cable only for new installations) Shielded Twisted Pair #18AWG (0.8mm) 1900m (6232 ft.)
Type B:	Multi-twisted Pair with shield #22AWG (0.32mm) 1200m (3936 ft.)
Type C:	Multi-twisted Pair without shield #26AWG (0.13mm) 400m (1312 ft.)
Type D:	Multi-core without twisted pairs and having an overall shield #16AWG (1.25mm) 200m (656 ft.)
Grounding aspects	Wiring is ungrounded. If bus wires are grounded or shorted, communication to all devices is interrupted. (short circuit protection is recommended)
Shielding	Shields should be grounded at only one point
Terminators	2 near each end of each bus segment
Hazardous Area Installations	Intrinsically Safe devices available
Device Addressing	Automatic when connected to segment
Governing Body	Fieldbus Foundation
Web Site	www.fieldbus.org

Conventional I/O System	FF Network
Advantages	Advantages
Technology is already understood	Excellent support for analog I/O
Slightly lower device cost	Incorporates discrete devices into same segments
Independent wiring from devices to the control system means wiring problems with one device don’t affect other field devices	Provides control in the field capabilities
Drawbacks	Provides redundancy options for power and communications devices
Higher installed cost	Available for Intrinsically Safe installations
Point-to-point wiring is expensive	Largely supported by process control manufacturers
Many wiring connections: - are labor intensive to install - create many points of failure - increase complexity when troubleshooting - require large amounts of cabinet or rack space for installation of terminal blocks - create time-consuming initial checkout and startup	Complete digital communications to transmitter microprocessors: - Eliminates inaccuracies of A/D and D/A conversions of analog representative signals, such as 4-20mA - Eliminates calibration of representative signals to improve accuracy - Eliminates setting of upper and lower range limits at the device level - Devices contain diagnostic information and alarming capabilities - Interoperability certification ensures that various field devices work with a variety of host systems, regardless of manufacturer
Expansion requires duplicating the entire wiring scheme for each additional point	Drawbacks
	Limited power requirements in Intrinsically Safe applications, extended for FISCO installations
	Segment power, grounding, and loading must be considered when designing segments
	Training for commissioning, troubleshooting, and calibration may be required
	Requires proper grounding and power isolation for error free network communications