Bus presentation

Notes de l'éditeur

• #2: The digital world continues to grow all around us and the same is true in the industrial environment. Fieldbus technologies and connectivity between various systems continues to evolve. Today’s integrated companies and control systems are often a combination of technologies, depending on the task to be performed. Industrial communications is no different with many “low speed” and now Ethernet based solutions available for specific needs. The challenge becomes selecting the right bus, correct route, and making sure that you have the proper connections for you complete trip. In addition to providing some insight into future developments in the process control communications arena (the route ahead), this presentation will provide participants an overview on the fieldbus options available and some general guidelines when to select which technology for the task at hand (correct route and bus).
• #4: Legend: Thick black lines represent multiconductor cables Thin black line for single pair analogue cable Orange line for Fieldbus cable Parallel MOXA green line for Industrial Ethernet LAN Parallel black lines for Commercial LAN market (i.e. CISCO)
• #5: Each of the communications techniques used in control have their “era” and the digital era has now begun with Fieldbus as the first and other such as wireless and ethernet in their infancy. Each generation has had a more rapid adoption rate than it predecessor.
• #6: These are just a few of the capital savings that are possible from using fieldbus technology (FF, Profibus, etc.) Fewer Terminations: In the case of FF approximately 50% reduction is possible Reduced Cable tray requirements: fewer cables and also multi-core cables but of smaller size. HART is also capable of multi-drop but I do not know of anyone doing it for control and only 1 or 2 people make I/O cards capable of doing so. Can explain in person so you can make your notes for that if you want.
• #7: Digital transmitters transmit the actual value and do not have the limitation of calibrated range. As long as the signal is in the operating range it is possible to get a reading. In addition digital transmitters have an order of magnitude more rangeability than analogue transmitters.
• #8: Installation cost – 2 slides earlier Signal integrity – previous slide Intelligence – diagnostics and signal processing Utility – broader range and flexibility
• #9: Some of the many different protocols and where they fit on the control/application spectrum CAN – used in automobiles and the basis for several other protocols LONworks – predominantly building automation, including most modern elevators Message here is that you must select the right protocol/tool for the job you are trying to do. FDT/DTM is one tool to provide you a more consistent interface across all the protocols.
• #10: Each protocol has varying degrees of each of these features including things like: Ease of access to the data (polling versus published) Speed at which data is available (network communication speed) Now will discuss each of the major protocols supported by FDT in more detail
• #11: Most widely used protocol in the process automation sector and most of today’s analog instruments support this capability. Latest version is HART 7, which includes WirelessHART. Each of the recent editions of the HART protocol have been adding increased functionality/features found in Foundation Fieldbus.
• #12: Frequency Shift Key (FSK) based protocol that is superimposed on the analogue signal. Maximum (burst) baud rate is 19.6 kbaud, though typical HART modem “speed” is 9600 baud.
• #13: Typical HART message showing how the analogue signal is changing and the magnitude/amplitude of the FSK message stays the same along the slope. HART can communicate additional PV information using protocol. Typically up to 4 process variables though more are possible. Communications are based on polling from master location so any information must be requested from the device by the host or asset management system. Depending on the size of the system it can take an extended period of time to access all the devices in a network.
• #14: Most widely used form of fieldbus communications. Use serial communications and also has an Ethernet “flavour” Modbus/TCP Two versions of Modbus RTU and ASCII. Modbus+ is Modicon proprietary and is not open.
• #15: Refer back to OSI model so that different methods of communications support the protocol. Most commonly used within a facility is RS-485 because it is multidrop. Bell 202 for SCADA systems that have not migrated to Modbus/TCP which is based on Ethernet.
• #16: Function codes fully defined by the specification and expected response. Example on next slide.
• #17: Ranges for various registers defined during configuration of the devices
• #18: Shows how Modbus (Layer 7 protocol) can be used with a variety of different physical layers, including Ethernet packets for Modbus/TCP without change being needed to the “Modbus specification” itself.
• #20: AS-i is a master slave communications protocol. VERY fast because each message is only 4 bits. Have the ability to support analogue by combining 2 messages and hence 8 bit resolution.
• #25: Supports both branching and daisy chain installation with Power in same cable as communications. Cable typically a thick (Like coax) 5 conductor cable.
• #26: Collision Sensing Multiple Access/Collision Arbritration (CSMA/CA) similar to original Ethernet
• #27: I simply read through each of the boxes on this page normally “clumped” together by topic Network power/Physical Media Terminators/Connections Wiring/maximum devices Distance/Drop budget Messaging Services Producer/Consumer means message is between 2 points on the network (one producing (generating) the message and the other consuming (receiving) it)
• #29: Relationships between different “flavours” of Profibus. Shows how Profibus PA must “flow through” Profibus DP for communications. OSI model for reference of where the similarities and common parts reside. IEC 1158-2 is the same as FF H1. 3 flavours of ProfNET as well. Slow (COM/DCOM), Medium (TCP/IP), and VERY FAST (IRT) which they developed the stack themselves for 3 axis controllers in factory automation. Has millisecond resolution.
• #30: Levels and traffic/loading at different levels of control system. DP & PA at Level 0 – sensor or field level Level 1 = Cell Level or controllers Level 2 = Factory Level or
• #31: Profibus DP requires separate power to each device. Typically used for On/Off and communications with motors Intrinsically Safe version of DP is now available as well.
• #34: 2 classes of Master. Class 2 is subservient to Class 1, though Class 1 can talk to each other peer-to-peer.
• #35: Note requirement for segment coupler/link. Typically as shown the coupler also serves as the Power Conditioner on the network as PA provides both power and signal.
• #37: Combining clock and data means there is a change a maximum of every 32 microseconds. – helps confirm network is working Transition from Up->Down = 0 and Down->Up =1 so magnitude is not what determines bit. Helps reduce susceptibility to noise.
• #38: Different ways to configure as per specifications though not all are used or recommended. Point to Point too expensive but is really a Tree with 0 spurs. Daisy Chain is like the Christmas Tree where if one bulb fails all lights are out and is therefore not used Spur is any drop of > 1 meter (3 feet) Can combine tree and spur, or like a tree have many JB with branches along a single trunk.
• #40: Increasing implementation of software (SCADA, OPC, SQL etc) Increasing use and emphasis on networks for process information and for real time control, communication and visualisation. Use of open networks with multi level communications (shop floor to top floor) providing integrated information and control systems. More intelligence (& diagnostics) at device level, greater speed and throughput. Greater interoperability and flexibility between manufacturers kit. Convergence of front office and production floor processes through s/ware. Increasing outsourcing of services eg project engineering and support functions (IT) Continual EU drive to lower cost of ownership, ROI and production costs The big question about the future of networks in the manufacturing environment is how many different networks do you need?
• #42: It’s important to realise that Ethernet is only the bottom two layers of the 7 layer model, although it often refers to the TCP/IP protocol suite as well. The OS is usually Windows but could be Unix or Linux for example. Email is a typical application, but then so is Internet Explorer! Each layer is independent of the ones above and below it. All the layers have to do is conform to the interfacing standards. This means that in theory instead of using TCP/IP you could use layers 3 and 4 of Profibus and run that on Ethernet! Alternatively you could run TCP/IP on the bottom two layers of Profibus.
• #49: Offer to answer any questions. Remind participants that ISA is the leading source of information for automation professionals and practitioners. Thank the attendees in Houston and online. Remind the Houston attendees that they can obtain the related resources as they leave the theater and save on shipping costs.