Digital
Communication
for Field Devices
and Data Acquisition
NIDHIN MANOHAR
Senior Research Engineer
We shall see…
• Digital communication?
• What is serial communication?
• Fieldbus?
• What has Wireless got to do
with fiel...
IEEE-488 (Parallel Data)
• Interface comprises 8 data lines, 8 control lines
and 8 ground lines.
• Up to 15 devices can be...
Digital serial communication
• Introduced with earliest Digital Computers
• Communicate between Central Computer
and perip...
RS-232C
• Electronic Industries Association (EIA)
• send and receive bytes of information one
bit at a time.
• Earlier, us...
RS-232C: What Is Handshaking ?
• for the data to be transmitted, both sides
must be clocking the data at the same
baud rat...
Serial RS-232C
RS-422, RS-423
• serial connection used on Apple Macintosh
computers.
• uses differential signal, as opposed to the
unbala...
RS-485
• improvement over RS422
• number of devices from 10 to 32
• defines electrical characteristics to ensure
adequate ...
Firewire IEEE-1394
• Also popular as Firewire. Featured on
laptops
• use of bus cable to power devices.
• Firewire transmi...
Firewire IEEE-1394
• uses a peer-peer protocol, similar to IEEE-488.
• standard cable has maximum length bus
comprises 16 ...
USB (Universal Serial Bus)
• serial data transmission,
• device powering,
• data sent in 1 ms packets.
• USB 1.1 has 1.5 a...
Ethernet (TCP/IP)
• Instruments with Ethernet interfaces
have great advantage: can be
interrogated and controlled from a
d...
MODBUS with RS-485
• messaging structure developed by
Modicon in 1979,
• master-slave/client-server communication
between ...
MODBUS with RS-485
• slave is any peripheral device (I/O
transducer, valve, network drive, or other
measuring device),
• M...
MODBUS
• devices include Register Map.
• MODBUS functions operate on these
registers to monitor, configure, and control
mo...
MODBUS: ASCII Transmission Mode
• American Standard Code for
Information Interchange
• each character byte in a message is...
MODBUS: RTU
• Remote Terminal Unit Mode,
• each 8-bit message byte contains two 4-bit
hexadecimal characters,
• message tr...
MODBUS MESSAGE FRAMING
• A message frame is used to mark the
beginning and ending point of a message
• receiving device de...
ASCII Mode Message frame
• messages start with colon ":" (ASCII 3AH)
end with a carriage return-line feed (CRLF,
ASCII 0DH...
RTU Mode Message Frames
• messages start with silent interval of atleast 3.5
characters
• when first field is received (ad...
• a silent interval of more than 1.5 char-times
before completion of frame (not a continuous
stream), causes receiving dev...
• MODBUS ADDRESSES
• MODBUS FUNCTIONS
• MODBUS DATA FIELD
• MODBUS ERROR CHECKING
– Parity checking of the data character ...
MODBUS with TCP/IP
Fieldbus?
• fully-digital, bidirectional
communication networking schemes for
automation and instrumentation
applications....
• concept of digital networking started
in the early 1970s
• large number of players in the
FieldBus each with own proprie...
Fieldbus Advantages
Fieldbus advantages over traditional
instrumentation
• Digital data eliminates analog conversions and
related drifts and c...
Open, InterOperable systems
• Open: to denote easy availability of
(licensed) technology to developers
and end-users for e...
Year
1976
1977
1980
1984
1988
1990
1991
1993
1994
1994
1994
1995
1995
1995
1996
-

Open and available
Ethernet
ARCNet
Remo...
• FIP : Factory Instrumentation
Protocol
• PROFIBUS : Process Field Bus
• CAN : Controller Area Network
• LonWorks
• P-Net...
IEC 61158
•FF version H1
•ControlNet
•Profibus (CENELEC EN-50170,
EN-50254)
•P-Net
•FF version HSE
•SwiftNet
•WorldFIP (Vo...
Bit-level sensor

Discrete
CAN

LONworks

Seriplex

Process

OCTOBUS : IEC61158

FF HSE

Ethernet

Profibus

WorldFIP
P-Ne...
PROFIBUS
• DP : Decentralised Periphery; high speed, simple field
level communications; Low cost.
• FMS : Fieldbus Message...
Current/mA

Profibus PA
0

1

1

0

0

+9mA
…Etc.

≥10mA
-9mA

time
Tbit = 32µs (f = 31.25kbit/s)
Profibus

• GSD (Generic Station Description)
files for PROFIBUS DP devices
Profibus Nutzerorganisation e.V. Karlsruhe : P...
Foundation Fieldbus
• 31.25kbps Physical Layer
• Signaling Method similar to smart transmitters
• Supply voltage through i...
FF
• Number of devices between 2 and 32.
• Trunk: twisted pair individual shielded 18AWG cable; cable length <1900m; else
...
FF
• only one device on a link is allowed to
communicate; Link Active Scheduler (LAS)
is the mediator.

• Address:
Virtual Field Devices
& Function Blocks
• device may contain user applications
independent of each other; do not
interact....
Function Block VFD
• three classes of blocks:
– Resource Block; manufacturer’s name, device name,

DD, etc.
– how much res...
Resources on the Web for
FieldBuses
• http://www.profibus.com/pall/meta/downloads
• www.interbus.com
• www.interbusclub.co...
• SCOPE Exists!
Discrepancies /
Errors, may be
brought to the
attention of
lecturer for
correction.

Teachers No Most of t...
Thank you!
For your patience & tolerance

m.suresh@fcriindia.com
HART Communication Protocol
• Bell-202 standard Frequency-shiftkeying (FSK)
• bit ‘1’ : 1200 Hz
• bit ‘0’ : 2200 Hz
• Baud...
HART Communication between
master and slave
• The master sends messages with
requests for actual/specified values,
and/or ...
HART Commands
• Universal commands
• Common practice commands
• Device-specific commands
• HART follows the Open Systems
Interconnections (OSI) model of the
International Organization for
Standardization (ISO).
...
Question
How do we make the
connection?
What signals can I
send?
How do I address a
message?
When can I send a
message?

T...
Digital communication for field devices...
Digital communication for field devices...
Digital communication for field devices...
Digital communication for field devices...
Digital communication for field devices...
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  • {"33":"International standardization organizations have worked for many years in order to get an agreement on a common fieldbus standard. But it seems that it is still a long way to go to get something comparable to the old 4 – 20 mA standard. Or – perhaps we never will get there. Among the existing fieldbuses some are better in one system, some other in another system.\nIn year 2000 it came a document, the IECC 61158 standard, which includes 8 different fieldbuses in the same standard. \n The 8 fieldbuses included in this Octobus standard are:\nControlNet\nFF – H1 (Foundation Fieldbus)\nFF – HSE (Foundation Fieldbus)\nInterbus\nP-Net\nPROFIBUS\nSwiftNet\nWorldFip\n \n"}
  • Digital communication for field devices...

    1. 1. Digital Communication for Field Devices and Data Acquisition NIDHIN MANOHAR Senior Research Engineer
    2. 2. We shall see… • Digital communication? • What is serial communication? • Fieldbus? • What has Wireless got to do with field-devices?
    3. 3. IEEE-488 (Parallel Data) • Interface comprises 8 data lines, 8 control lines and 8 ground lines. • Up to 15 devices can be interconnected on one bus. • Each device assigned a unique primary address, ranging from 4-30, by setting the address switches on the device. • Devices are linked in either a daisy-chain or star (or some combination) configuration • up to 20 m of shielded 24-conductor cable. • A maximum separation of 4 m is specified between any two devices, and an average of 2m over the entire bus. • Data transfer at 1 Mbps
    4. 4. Digital serial communication • Introduced with earliest Digital Computers • Communicate between Central Computer and peripheral devices • Mainframe and distributed terminals • Initially, specified for Distances 15-20 feet, upto 50feet • interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE)
    5. 5. RS-232C • Electronic Industries Association (EIA) • send and receive bytes of information one bit at a time. • Earlier, used to be slow (Compared to parallel data communication) • But is simpler and good for longer distances • Distances > 1km (with repeaters OR Modems) • baud rate, data bits, stop bits, and parity
    6. 6. RS-232C: What Is Handshaking ? • for the data to be transmitted, both sides must be clocking the data at the same baud rate. • In many applications, problems due to overloading receivers. • handshaking helps in asynchronous communication. • Three most popular handshaking are: – – – software handshaking, hardware handshaking, and Xmodem.
    7. 7. Serial RS-232C
    8. 8. RS-422, RS-423 • serial connection used on Apple Macintosh computers. • uses differential signal, as opposed to the unbalanced signals referenced to ground with RS232. • two lines each for transmit and receive signals, • results in greater noise immunity and longer distances as compared to RS232. • advantageous for industrial applications
    9. 9. RS-485 • improvement over RS422 • number of devices from 10 to 32 • defines electrical characteristics to ensure adequate signal voltages under maximum load. • enhanced multidrop capability to network of devices to a single RS485 serial port • RS485 is a superset of RS422; • all RS422 devices may be controlled by RS485
    10. 10. Firewire IEEE-1394 • Also popular as Firewire. Featured on laptops • use of bus cable to power devices. • Firewire transmits data in packets and incurs some overhead as a result. • Devices when used in isochronous mode, guarantees a time slot for data transfer in every frame. • Firewire frames are 125 msec long • transfer speed of 400 Mbit/s but may result in substantially slower responses to instruments' service requests.
    11. 11. Firewire IEEE-1394 • uses a peer-peer protocol, similar to IEEE-488. • standard cable has maximum length bus comprises 16 hops of 4.5m each. • Each hop connects two devices, • but each physical device can contain four logical nodes. • A Firewire cable contains two twisted-pairs (signals and clock) and two untwisted conductors (power and ground). • FireWire is 'hot pluggable' • devices operating at different communication rates can co-exist on the same communications chain, though a slower device must not be placed between two higher speed devices.
    12. 12. USB (Universal Serial Bus) • serial data transmission, • device powering, • data sent in 1 ms packets. • USB 1.1 has 1.5 and 12-Mbit/s speeds • USB 2.0 has signaling rate from 12 MHz to 480 MHz • PCs, Laptops, devices, etc.
    13. 13. Ethernet (TCP/IP) • Instruments with Ethernet interfaces have great advantage: can be interrogated and controlled from a desktop anywhere in the world. • A 'web enabled' device behaves like a website and can be operated with standard browser. • Fast data transfer up to 1GB/s if the network infrastructure is good.
    14. 14. MODBUS with RS-485 • messaging structure developed by Modicon in 1979, • master-slave/client-server communication between intelligent devices. • master initiates transactions (queries). Slaves respond with requested data to the master, or takes action requested in the query.
    15. 15. MODBUS with RS-485 • slave is any peripheral device (I/O transducer, valve, network drive, or other measuring device), • Masters address individual slaves, or initiate a broadcast message to all slaves. • Slaves return response to all queries addressed to them individually, but not to broadcast queries
    16. 16. MODBUS • devices include Register Map. • MODBUS functions operate on these registers to monitor, configure, and control module I/O • Standard MODBUS networks employ one of two types of transmission modes: – ASCII Mode – RTU Mode.
    17. 17. MODBUS: ASCII Transmission Mode • American Standard Code for Information Interchange • each character byte in a message is sent as 2 ASCII characters. • allows time intervals of up to a second between characters during transmission without generating errors
    18. 18. MODBUS: RTU • Remote Terminal Unit Mode, • each 8-bit message byte contains two 4-bit hexadecimal characters, • message transmitted in a continuous stream. • Greater effective character density increases throughput over ASCII mode at same baud rate.
    19. 19. MODBUS MESSAGE FRAMING • A message frame is used to mark the beginning and ending point of a message • receiving device determines which device is being addressed • knows when message is completed. • partial messages detected and errors flagged
    20. 20. ASCII Mode Message frame • messages start with colon ":" (ASCII 3AH) end with a carriage return-line feed (CRLF, ASCII 0DH & 0AH). • The only allowable characters for all other fields are hexadecimal 0-9 & A-F. • each character requires 7 data bits. Thus, each character is 10 bits with start bit, parity bit, and stop bit of the data frame.
    21. 21. RTU Mode Message Frames • messages start with silent interval of atleast 3.5 characters • when first field is received (address) after silent interval of at least 3.5 char-times, device decodes it to determine if it is being addressed. • Following the last character transmitted, a similar silent interval of 3.5 char-times marks end of message • a new message can begin after this interval.
    22. 22. • a silent interval of more than 1.5 char-times before completion of frame (not a continuous stream), causes receiving device to flush the incomplete message • the immediate next byte is assumed to be address field of a new message • if new message begins earlier than 3.5 chartimes following previous message, receiving device assumes it is continuation of previous message. • This will generate a CRC error
    23. 23. • MODBUS ADDRESSES • MODBUS FUNCTIONS • MODBUS DATA FIELD • MODBUS ERROR CHECKING – Parity checking of the data character frame (even, odd, or no parity) – Frame checking within the message frame (Cyclical Redundancy Check in RTU Mode, or – Longitudinal Redundancy Check in ASCII
    24. 24. MODBUS with TCP/IP
    25. 25. Fieldbus? • fully-digital, bidirectional communication networking schemes for automation and instrumentation applications. • term much misunderstood; referred to by different cartels of manufacturers and vendors to advance their own versions of networking products and brands at the expense of products from other groups.
    26. 26. • concept of digital networking started in the early 1970s • large number of players in the FieldBus each with own proprietary digital communication protocols • exercise high degree of caution and reluctance to acceptance of FieldBuses. • fears of unavailability of support-aftersales, • fear of technology getting obsolete, • high cost of proprietary technologies due to lower competition, etc.
    27. 27. Fieldbus Advantages
    28. 28. Fieldbus advantages over traditional instrumentation • Digital data eliminates analog conversions and related drifts and calibration issues. • Significant reduction in the amount of wiring, cable trays etc. • extensive bi-directional data communication for diagnostic information, device parameters, etc. • Centralised commissioning of devices. • Asset management capabilities. • Greater flexibility in system layout and design. • Ease of future expansion and modification.
    29. 29. Open, InterOperable systems • Open: to denote easy availability of (licensed) technology to developers and end-users for enhancements or product developments • InterOperable: easy availability of products and services for any particular technology from multiple sources; to mix and match from different suppliers
    30. 30. Year 1976 1977 1980 1984 1988 1990 1991 1993 1994 1994 1994 1995 1995 1995 1996 - Open and available Ethernet ARCNet Remote I/O Interbus-S WorldFIP Seriplex LonWorks AS-I (Actuators DeviceNet Profibus-DP Smart Distributed Profibus-PA (process CAN Open FOUNDATION ControlNet Modbus Plus Modbus RTU/ASCII Profibus-FMS Technology Developer DEC, Intel, Xerox Datapoint Allen-Bradley / Rockwell Phoenix Contact, Interbus-Club WorldFIP orgn. Automated Process Control Echelon AS-I consortium Allen-Bradley/ Rockwell Siemens, PNO Honeywell (MICROSWITCH) Siemens, PNO CAN in Automation, Phillips FIELDBUS FOUNDATION Allen-Bradley/ Rockwell Modicon Modicon PNO, Siemens
    31. 31. • FIP : Factory Instrumentation Protocol • PROFIBUS : Process Field Bus • CAN : Controller Area Network • LonWorks • P-Net • AS-I • WorldFIP • ISP : InterOperable Systems Project • FF : Foundation FieldBus • Industrial Ethernet
    32. 32. IEC 61158 •FF version H1 •ControlNet •Profibus (CENELEC EN-50170, EN-50254) •P-Net •FF version HSE •SwiftNet •WorldFIP (Vol.3 of EN-50170) •Interbus-S
    33. 33. Bit-level sensor Discrete CAN LONworks Seriplex Process OCTOBUS : IEC61158 FF HSE Ethernet Profibus WorldFIP P-Net FF H1 SDS DeviceNet Ethernet Business SwiftNet ControlNet ModBus Ethernet Profibus DP Profibus FMS Control AS-i Interbus Device Sensor loop Fieldbuses and the IEC61158 standard Automation Application
    34. 34. PROFIBUS • DP : Decentralised Periphery; high speed, simple field level communications; Low cost. • FMS : Fieldbus Message Specification; Higher-end, applications level communications. • PA : Process Automation; Developed specifically for process industry, very cost effective two-wire connection carrying both power and data. • PROFInet : Simlar to FF-HS version, is the Ethernet stream of Profibus. • PROFIDrive : Drive control; Deterministic operation (sub micro-second timing for servo and drive synchronisation). • PROFISafe : Safety related; High Integrity Emergency stop systems, safety interlocks and safety-shutdown systems.
    35. 35. Current/mA Profibus PA 0 1 1 0 0 +9mA …Etc. ≥10mA -9mA time Tbit = 32µs (f = 31.25kbit/s)
    36. 36. Profibus • GSD (Generic Station Description) files for PROFIBUS DP devices Profibus Nutzerorganisation e.V. Karlsruhe : PNO
    37. 37. Foundation Fieldbus • 31.25kbps Physical Layer • Signaling Method similar to smart transmitters • Supply voltage through impedance conditioner, (typically inductors). • DC current through impedance conditioner feeds devices. • Supply voltage between 9V and 32V at device terminals. • The impedance conditioner ensures output impedance of the power supply is higher than 400Ω in the signal frequency bandwidth.
    38. 38. FF • Number of devices between 2 and 32. • Trunk: twisted pair individual shielded 18AWG cable; cable length <1900m; else <1200m • Spurs: <120m total; depends on no. of devices
    39. 39. FF • only one device on a link is allowed to communicate; Link Active Scheduler (LAS) is the mediator. • Address:
    40. 40. Virtual Field Devices & Function Blocks • device may contain user applications independent of each other; do not interact. • Management VFD where network and system management applications reside. used to configure network parameters and manage devices • Function Block VFD ; possible for a field device to have two or more Function Block VFDs.
    41. 41. Function Block VFD • three classes of blocks: – Resource Block; manufacturer’s name, device name, DD, etc. – how much resource (memory and CPU time) is Available, – Status of hardware, – controls the overall device hardware and Function Blocks – Function Block; – Standard Block as specified by Fieldbus Foundation, – Enhanced Block with additional parameters and algorithm, – Open Block (Vendor-specific) designed by individual vendors. – Transducer Block.
    42. 42. Resources on the Web for FieldBuses • http://www.profibus.com/pall/meta/downloads • www.interbus.com • www.interbusclub.com • www.phoenixcontact.com • www.fieldbus.com.au/techinfo.htm • www.ee.latrobe.edu.au/~stanley/infoseek.htm • www.lonworks.com • http://www.p-net.dk/fieldbus/fieldbus.html
    43. 43. • SCOPE Exists! Discrepancies / Errors, may be brought to the attention of lecturer for correction. Teachers No Most of the times!
    44. 44. Thank you! For your patience & tolerance m.suresh@fcriindia.com
    45. 45. HART Communication Protocol • Bell-202 standard Frequency-shiftkeying (FSK) • bit ‘1’ : 1200 Hz • bit ‘0’ : 2200 Hz • Baud rate : • 1200 bit/s • Signal structure: • 1 start bit • 8 data bits • 1 bit for odd parity • 1 stop bit.
    46. 46. HART Communication between master and slave • The master sends messages with requests for actual/specified values, and/or any other data/parameters available from the slave device. • The slave interprets these instructions as defined in the HART protocol. • The slave responds with status information and data for the master.
    47. 47. HART Commands • Universal commands • Common practice commands • Device-specific commands
    48. 48. • HART follows the Open Systems Interconnections (OSI) model of the International Organization for Standardization (ISO). • The HART protocol uses a reduced OSI model, implementing only layers 1, 2 and 7 • • • Layer 1, Physical Layer Layer 2, Link Layer Layer 7, Application Layer
    49. 49. Question How do we make the connection? What signals can I send? How do I address a message? When can I send a message? Topics OSI layer Plugs, sockets, cable Physical Voltage, current, frequency Physical None (point-to-point), numerical address, tag Access rules: master-slave, tokenpassing, collision-detection Data Link Data Link Data Link Coding: bits, characters, parity What messages can I send? What does a message mean? Data types: bits, integers, floating point, text App. Standard functions App. Function blocks, Device Descriptions "User"*
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