1. Fieldbus networks replace traditional 4-20 mA analog signals with digital communication over twisted-pair wiring. 2. The key changes are replacing the analog control system and field devices with digital ones that communicate over FOUNDATION fieldbus, and adding terminators to the wire pairs. 3. Devices can be connected in a bus, tree, daisy chain, or point-to-point topology with optional repeaters, bridges or gateways to extend the network or connect different segments.

2. Building the Network

3. The only changes are:
1. The control system‟s 4-20 mA interface is
replaced with one that “talks” FOUNDATION
fieldbus. We called it a FOUNDATION Fieldbus
Interface (FFI). This FFI could, in fact, be in a
personal computer or a PLC.
2. The analog field device is replaced with one that
talks FOUNDATION fieldbus.
3. A terminator is added at the FFI end of the wire
pair. Another terminator is added at the field device
end of the wire pair. The FFI may have a built-in
terminator so that you don‟t have to add one.

6. Fieldbus Segment

8. Segment Calculation

9. Fieldbus Network With Additional Devices Added
Fieldbus Network With Chained Devices

10. Repeaters are active bus powered, or non-bus powered
devices, used to extend a fieldbus network.
A maximum of four (4) repeaters and/or active couplers can be
used between any two devices on a fieldbus network Using four
repeaters, the maximum distance between any two devices on that
network is 9500 m.
A Bridge is an active bus powered, or non-bus powered
device, used to connect fieldbus segments of different
speeds (and/or physical layers - e.g. wire, optical fiber,..)
together to form a larger network.
A Gateway is an active bus powered, or non-bus powered
device, used to connect a fieldbus segment or segments to
other types of communications protocols (e.g.
Ethernet, RS232, ..).

11. Addition of a Device and a
Bridge to Fieldbus Network

12. Spurs and Repeaters

13. Repeater Connection

14. Shielding (Screening)

15. Polarity
The Manchester signal used by fieldbus is an alternating voltage that
changes polarity once or twice per bit.
In unpowered networks only this alternating voltage exists.
In powered networks the alternating voltage is superimposed onto the DC
voltage being used to power the devices.
In either case, the fieldbus receive circuits look at only the alternating
voltage.
Positive voltage swings have one meaning, negative swings have the
opposite meaning.
Therefore, the fieldbus signal is polarized. Field devices must be connected
so that they all see the signal in correct polarity.
If a field device is connected “backwards” it will see an inverted version of
the alternating voltage and won‟t be able to communicate.

16. Short Circuit Protection
Short circuit protection has logic that detects a
short, removes the shorted circuit from the segment, and
lights a LED. This prevents a short from affecting the
segment.

18. DC Power for Two-Wire Field
Devices

19. If you have 2-wire field devices in your network, you
have to make sure they have enough voltage to
operate.
Each device should have at least 9 volts.
You need to know:
1. The current consumption of each device.
2. Its location on the network.
3. The location of the power supply on the network.
4. The resistance of each cable section.
5. The power supply voltage.

21. Installation

22. Powered and Unpowered

23. Bus Topology

24. Tree Topology

25. Daisy Chain Topology

26. Point-to-Point Topology

27. Terminators
A terminator is an impedance
matching module used at or near
each end of a transmission line.
There need to be two (and ONLY
TWO) terminators per bus segment.
The terminators prevent distortion
and signal loss, and are typically
purchased and installed as a
preassembled, sealed module.
The user/installer need not be
concerned about or assemble
individual electrical resistors and
capacitors.

28. Terminal Blocks
Terminal blocks can be the same terminal blocks as used for 4-20 mA.
The terminal blocks typically provide multiple bus connections, such that a device
can be wired to any set of bus terminals.

31. Power Supply
• Wide input range:
90-264 VAC (47-440 Hz)
127-367 VDC
• 24 VDC, 1.5 A output.
• Galvanically isolated
• Failure indication and output

32. Power Conditioner
•A fieldbus power conditioner prevents the high frequency
communications signal from being shorted out by the DC
voltage regulators.
•Typical power conditioners make 350 to 500mA available
on the bus.

33. Grounding

34. Preferred Earthing Arrangement

35. Alternative earthing arrangement for improved
EMC performance

36. Multiple grounding with potential equalization

37. Wiring DOs and Don’ts
Normal wiring procedures apply:
• No loose connections
• No exposed conductors
• Water proof junction boxes
• Signal wires not too close to power wires
• No safety barriers in parallel

38. Interface Connection

39. Basic Troubleshooting
• Correct polarity
• Correct tag and address
• Integrity of the fieldbus network
• Supply voltage is sufficient, min 9.5 V even during
communication.
•Wiring errors, including wrong connections, open or short
circuits, intermittent
•Connections and reversed polarity
• Too many or too few terminators on each segment
• Faulty „out of the box‟ physical layer components or
fieldbus instruments
• Inadequate grounding, such as multiple grounds in field, or
the absence of any
clear grounding strategy

40. Communication Errors
• Poor connections
• Wrong or no terminator placement
• Too low or unstable power supply
• Too long or over-populated spurs
• Wrong or no grounding
• Water filling due to poor plugs and cable-glands

41. Troubleshooting

42. Periodic monitoring
• Short-circuits between the fieldbus + or – and the cable shield.
• The signal level of each participant on the bus. A minimum level is
specified by Foundation fieldbus specifications. Low or high levels on all
devices suggest incorrect bus termination, but if the faulty signal level is
only on one device, there is possibly a problem on a single spur.
• DC voltage on the bus, indicating correct functioning of power
supply/conditioner.
• Noise: A maximum level is specified by Fieldbus specification.
• Retransmissions. This provides a good measurement of physical layer
health; retries can obscure faulty device or network.

43. Tools

46. Signals

47. Multiple Fieldbus Frames

48. Signal Distortion

52. Troubleshooting Tables

55. Oscilloscope Captures

61. Bad Installation

62. Bad Installation

63. Bad Installation

64. Configuration

65. Transducer Display

66. Local Adjustment

67. Redundancy
•No provision is made within either fieldbus
standard for redundant segment
communications.
•Various fieldbus vendors, including major
process control companies, have developed
redundant fieldbus schemes that involve
complete duplication of all equipment.

70. Power Conditioner
Redundancy

71. Galvanic Isolation

72. Fault-Tolerance with Redundant H1
Cards

73. Cabling

74. Cable Characteristics