Technical Article Interface Technology Considerations for HMI Systems

A well-organized, easy-to-use panel An HMI System provide the controls by Connecting/communicating with an HMI System may be what the user sees first in an which a user operates a machine, system, Typically, communication can be achieved Human Machine Interface (HMI) System, or process, and encompasses all the through several approaches: hard-wired, but the choice of communications and elements a person will touch, see, hear, or serial or . Each approach has connectivity technologies is just as critical use to perform control functions and pros and cons — selection will depend on to the system’s successful use. receive feedback on those actions. A the final application. well-functioning HMI System makes the operation of the equipment or systems Hard-wired connections under control transparent to the user, Hard-wired systems require no special enabling an efficient, harmonious align- tools and are simple, visible, and easy to ment of operating equipment to task. understand, especially where the HMI interface controls a single machine. Hard The effectiveness of the HMI — and wiring has limitations, including: consequent enhanced productivity of the ‚‚ Difficulty integrating changes or new user — depends upon an exacting design features that require new wiring. process that incorporates all technical, ‚‚ Increased space and weight ergonomic, and commercial application requirements, due to the number of requirements. Equally important, the wires and connectors, incurring higher choice of communications and connectivi- fuel costs for transport vehicles. ty technologies linking the HMI to the core In the rolling stock industry, many users application. continue to choose hard-wired HMI

www.eao.com Differing market segment connectivity requirements have caused many different bus standards to be defined and deployed. Some offer faster reaction times, others allow more devices or larger data transfers.

“Bus systems provide a wide (which in transportation range of advantages over hard translates into lower fuel wired connections, including costs). There are trade-offs, easy addition of new function- however: systems are more ality — typically through complex when only a small — without adding or number of inputs and outputs replacing hardware.” (I/O points) are required. Also, special tools and well-trained “Buses for specific applica- personnel are required to tions include BACnet, LonTalk, design and service a bus Konnex, -Bus and, others for system. Bus connections incur building ; and LIN, slightly higher upfront costs, J1939, FlexRay, and others for but these are outweighed by automotive/transportation increased performance and applications.” long-term savings.

Selecting a bus technology Hard-wired systems require no special tools and are simple, visible, and Differing market segment easy to understand. connectivity requirements have caused many different bus Systems because the prohibitive costs and inconvenience of standards to be defined and changing operating controls across large working fleets out- deployed. Some systems offer weighs the enhanced efficiency, performance, and revenues faster reaction times, whereas generated by newer connectivity technologies. others may allow for more devices to be connected or for bus systems larger amounts of data to be As equipment and control systems became more complex and transferred. Buses for specific data hungry, transmission of data became a critical issue. Data applications include BACnet, transmission depends on distance and speed. The longer the LonTalk, Konnex, C-Bus and, cable length, the lower the transmission speed to keep bit-error others for ; rates acceptable. Industries such as semiconductor production, and LIN, J1939, FlexRay, and machinery, medical, process industries, and transportation use others for automotive/ bus connections extensively because of the need for reliable, transportation applications. real-time operations and work-in-process feedback. There are also connection Advantages of serial bus connectivity systems like the Actuator Bus systems provide a wide range of advantages over hard wired Sensor Interface (AS-i). connections, including easy addition of new functionality — typi- Networks comprised of cally through software — without adding or replacing hardware. sensors, actuators, pushbut- Wiring is much simpler and more flexible with smaller cables and tons, and valves can use this connectors allowing for more compact design, and easier system for a more intelligent hardware updating and relocation. Buses reduce subsystem method of cabling in control installation time and simplify fault identification with on-board environments. It offers many of diagnostic features. Bus systems also allow for any combination the benefits of more complex of information from multiple different sources to control output bus systems at a lower cost devices. In order to facilitate faster data transmission rates, and provides a complementary devices incorporated serial bus connections. Buses bring all the and reliable way to connect switching and illumination wires out as one data connection, binary and analogue devices. It reducing wiring, assembly, repair/maintenance time, and weight is suitable for interfacing to

www.eao.com . 2 Special tools and well-trained personnel are required to design and service a bus system. Slightly higher upfront costs are outweighed by increased performance and long-term savings.

“Field buses include: PROFIB- For other industrial applica- US, DeviceNet, ControlNet, tions, there are now additional CAN/CANOpen, KeyLink, protocol layers that format InterBus, Foundation Field data to enable efficient data Bus, and HART.” exchange across different networks, buses, and pieces of “The EtherCAT industrial equipment. All bus technology protocol (a specific is based on the Open System version of Ethernet) was Interconnection (OSI) seven developed for the semiconduc- layer standard. This standard tor production environment defines seven layers of and is now used in a wide interconnectivity from the variety of semiconductor and (Layer 1) through flat panel display manufactur- data link, network, transport, ing operations.” session, presentation, to application. For example, technology defines the bottom CANOpen modules could be used in transportation, marine, medical, or two layers, the physical layer machinery applications. An embedded version would be utilized for higher and the . The volume applications. CAN protocol specifies how packets of data may be higher level networks and is especially useful in harsh environ- transported from one point to ments. another using a shared communications medium. Field bus protocols evolved for interconnecting industrial drives, Higher level functions like flow motors, actuators, and controllers. Field buses include: PROFIB- control, node addresses, how US, DeviceNet, ControlNet, CAN/CANOpen, KeyLink, InterBus, to establish communications, Foundation Field Bus, and HART. For example, a CANBus and other capabilities are built module can connect switch controls, potentiometers, pilot lights, in an HLP (higher layer and other components as part of an integrated HMI System protocol) like DeviceNet, to sit interface, configured to enable plug-and-play capability. CAN on top of the basic CAN (controller–area network) is a message based protocol, designed technology. specifically for automotive applications to interconnect and communicate without a host computer. Currently it is also used in CAN (Controller Area Network) a range of industrial automation, transportation, and medical CAN was developed as a equipment applications. network for distributed real-time systems. CAN is a Higher level networks connect with field bus protocols primarily multimaster, asynchronous across variations of Ethernet. These include: PROFINET, Ether- serial bus. Its low guaranteed net/IP, EtherCAT, , -TCP, and SERCOS maximum latency makes it III. The EtherCAT protocol (a specific version of ideal for real-time applications. Ethernet) was developed for the semiconductor production It also delivers a high level of environment and is now used in a wide variety of semiconductor safety, making it well-suited for and flat panel display manufacturing operations. EtherCAT harsh environments. While provides superior performance, bandwidth, and topology developed for automotive use, flexibility to cover the entire range of communications require- with its low cost, ease of ments in semiconductor manufacturing equipment with a single implementation, and fast technology: from process control via control computer integration communication, short reaction to high-end motion control applications. time, timely error detection,

www.eao.com . 3 KeyLink is a simple communications protocol which allows for fast and easy integration. It features a simple point-to-point connection without setting an address for each connection.

“CANOpen is a standard length of 40 m and a fixed defined and widely used in Baud rate of 250 kBaud. There Europe and North America.” is no galvanic isolation required between the controller “J1939 is widely used in and the bus section. J1939 is commercial vehicles.” widely used in commercial vehicles. “DeviceNet is a low level network designed to connect KeyLink industrial devices like sensors KeyLink is a simple communi- and actuators with high-level cations protocol which allows devices, like controllers.” for fast and easy integration into an existing bus system such as CANOpen or . KeyLink features a simple point-to-point connection without setting an address for KeyLink: inputs and outputs are connected using a serial half- or full-duplex each connection. Inputs and interface. There can be up to 128 I/O points. outputs are connected using a serial half- or full-duplex and quick error recovery and repair, CAN is now used for industri- interface. There can be up to al applications, medical equipment and other real-time control 128 I/O points. systems. The CAN standard includes a physical layer and a data link layer that defines a different message types, arbitration rules KeyLink allows for separation for bus access, and methods for fault determination and fault of the power and control units. confinement. CAN uses CSAM/ CD with non-destructive bitwise The switching load is defined arbitration to ensure low latency and maximal bus utilization. In by the relay in the master contrast to Ethernet, CAN communication is data-oriented and power unit instead of the not destination oriented. CAN networks have maximum 64 nodes. KeyLink switch. The basic configuration of the master and CANOpen slave is done automatically. CANOpen is a standard defined and widely used in Europe and Two analogue signals can be North America. It builds on CAN and adds Higher Layer Protocols captured for each direction (HLP). It is designed for a maximum of 110 nodes with a maxi- and re-sent as PWM signals. mum wire length to 500 m at 125 kBaud with twisted pair cable The analogue signals can be available for higher rates. CANOpen supports flow control, device used to control brightness or addressing, and transporting of data blocks larger than one analogue outputs. KeyLink also message. An example of device addressing can be seen in has two selectable transmis- setting the brightness of LEDs through a CANOpen slave module. sion speeds. Extended The slave module can control the brightness of up to 128 outputs. systems capabilities include In addition, an individual set-point can be transferred to every bus input for more complex participant via the CANOpen master. CANOpen is typically used applications, and configuration as a slave device to collect data from switches and send informa- storage on the switching tion to digital outputs. It is used in the automotive industry, public source. transportation including railway and buses, marine applications, medical, and machining. DeviceNet DeviceNet is a low level CAN J1939 network designed to connect J1939 is designed for a maximum of 30 nodes with a maximum industrial devices like sensors

www.eao.com . 4 The difference between Ethernet and bus protocols the use of the TCP/IP protocol. Ethernet can connect to a LAN/WAN as well as the Internet. Where remote access is important, Ethernet wins.

“PROFIBUS is popular in HART manufacturing, process HART, Highway Addressable automation, and building Remote Transducer, is automation.” accepted as an industry standard for digitally enhanced “The difference between 4-20 mA communication with Ethernet and bus protocols of smart field instruments. The any kind, is Ethernet’s use of HART protocol was designed the TCP/IP protocol.” specifically for use with intelligent measurement and control instruments which traditionally communicate using 4-20 mA analogue signals. The HART protocol permits the process variable to continue to be transmitted by the analogue signal, while PROFIBUS is popular in manufacturing, process automation, and building additional information pertain- automation. ing to other variables, parame- ters, and device configuration, and actuators with high-level devices, like controllers. The calibration and diagnostics are strength of DeviceNet is the interchangeability of very low-cost transmitted digitally at the devices, typically used in manufacturing applications. Devices same time. might include switches, sensors, motor starters, bar code readers, etc. DeviceNet builds on the CAN technology and adds Ethernet the media and application layers. DeviceNet allows for hot Ethernet is used as the basis insertion of devices without powering down the network. It also for a higher level network. The provides for up to 64 node addresses on a single network. difference between Ethernet and bus protocols of any kind, Foundation is Ethernet’s use of the TCP/IP Distributed process control applications are addressed by protocol. TCP/IP allows Foundation Fieldbus. This bus has the ability to integrate Ethernet to connect to a LAN/ functions that are part of the field device itself, thereby distribut- WAN as well as the Internet. ing control throughout an implementation, as opposed to a This can deliver physically centralized control architecture. Foundation Fieldbus is a popular larger networks with greater selection when the application calls for the use of smart devices. data carrying capacity than a The key to success is using devices “certified” by the Fieldbus bus architecture like CAN. Foundation and creating device descriptions for each device. By Where real-time response defining a device’s capabilities, an attached controller is quickly through the network is critical, able to “learn” the device’s functionality. CAN provides a better choice. Where remote access is PROFIBUS important, Ethernet wins. PROFIBUS is popular in manufacturing, process automation, and There are now available building automation. It can be used where high-speed data Ethernet-based bus protocols transmission between controllers and I/O points is critical or for such as PROFINet, Ethernet/ complex communications between programmable logic control- IP and Ethernet Powerlink that lers (PLCs). PROFIBUS can be used at both the field/ device level are hoping to capture some of or manufacturing cell level. the capabilities of bus proto- cols while keeping the

www.eao.com . 5 The technical framework of bus systems is more sophisticated than hard-wired in terms of controlling data flow. The more ways a system supports assignment, the greater the effort required to get the right configuration.

“The presence of multiple contact with the bus. devices requires resources to ‚‚ The content of the data. In regulate the exchange of data this case, the data set and ensure that it’s transferred supplies the identification. and identified correctly — each device must be identifiable so This issue illustrates the neces- that the source or the content sity of choosing the right bus of the data can be assigned for a specific application. The appropriately.” technical framework of bus-connected systems “The technical framework of becomes more sophisticated bus-connected systems than hard-wired systems in becomes more sophisticated terms of controlling data flow. than hard-wired systems in The more ways a system terms of controlling data flow.” supports assignment, the greater the effort required to get the right configuration and, Wireless communications can deliver real-time data transmission, in the event of disruption, to application mobility, and remote management capabilities. identify the reasons for the failure. Software and on-board advantages of TCP/IP. Open access technology is critical for provides a acceptance of Ethernet-based protocols in many markets. versatile and efficient way to configure and control HMI USB subsystems, as well as In addition to the above-mentioned technologies, there are also encryption technology for connections between industrial networks and USB connections. PIN-protected secure access USB hubs and ports can connect industrial wired and wireless and other high-level data system to this PC- based communication system. For hot swap of management capabilities. devices, and plug-and-play among PCs and a variety of peripher- als. Using USB 2.0 hubs, typically housed in rugged enclosures, Wireless connections/communi- industrial USB communications support noise reduction for harsh cations environments, low power requirements, and good data speed at Industrial applications have 480 Mbits/second. However, USB was not really designed for employed wireless technolo- industrial use — any single bus segment can’t exceed 5 m, and gies over the last 20 years to there’s no provision for signal isolation. USB 2.0 finds its most take advantage of real-time common use in converters for serial-to-USB or Ethernet-to-USB. data transmission, application mobility, and remote manage- The right bus for the application ment capabilities. WWANs HMI control panel assemblies have embedded interfaces that link (wireless wide-area networks) them with the core system through serial communications utilize mobile communication connection, usually on the same transmission medium. The networks such as cellular, presence of multiple devices requires resources to regulate the UMTS, GPRS, CDMA2000, exchange of data and ensure that it’s transferred and identified GSM, CDPD, Mobitex, HSDPA, correctly — each device must be identifiable so that the source or , and WiMax. These the content of the data can be assigned appropriately. networks offer wide service coverage and are normally Assignments are made according to either: used for citywide, nationwide, ‚‚ The specific response of an individual device — which must or even global digital data have a unique address in order for the system to regulate exchange. In cellular communi-

www.eao.com . 6 ZigBee is popular for its low power requirements, network scalability, and reliability. It is often used to drive a diverse set of sensor network applications.

Contact cation, GSM (Global System for Mobile Commu- range needs. ZigBee is popular for its low power nication) is the leader with over 80% market requirements, network scalability, and reliability. EAO AG share, followed by CDMA (Code Division It is often used to drive a diverse set of sensor Tannwaldstrasse 88 Multiple Access). The biggest issues regarding network applications. ZigBee uses mesh CH-4601 Olten, Switzerland data exchange over a WWAN are the associated networking. Networks can scale to hundreds Tel. +41 62 286 91 11 costs, bandwidth, and IP management. and thousands of devices and all communicate Fax +41 62 296 21 62 However, as technologies improve and costs using the best available path for reliable [email protected] drop, WWAN is predicted to replace traditional message delivery. If one path fails, a new one is microwave, RF (), and satellite automatically discovered without affecting More information communication due to lower infrastructure system operation. This provides long-term www.eao.com/downloads costs. Popular wireless communication reliability. technologies that are being applied to industrial applications are WiFi, , ZigBee, and UWB UWB. All are based on IEEE 802 standards: WiFi UWB is gaining attention as an indoor, short- 802.11a /b/g; Bluetooth 802.15.1; ZigBee range, high-speed wireless communication. 802.15.4; UWB 802.15.3. With a bandwidth over 110 Mbps, it can satisfy most multimedia applications such as audio and WiFi video delivery and can act as a wireless cable WiFi was developed for data-intensive commu- replacement of a high speed serial bus such as nications — accessing the Internet, streaming USB 2.0 and IEEE 1394. video — typical web browser behaviour. WiFi devices communicate via radio signals that Summary must penetrate solid objects to reach other The effectiveness of the HMI System — and nodes. Transmitter power consequent enhanced productivity of the user output and antenna type are important consid- — depends upon an exacting design process erations. In an industrial environment, other that incorporates all technical, ergonomic, and machinery often produces a large amount of communication requirements. Connectivity electrical noise. WiFi for industrial applications technologies linking the HMI to the core typically is more robust. application directly affects both operator and overall system performance. This key intercon- Bluetooth nection is critical to overall successful use of the Bluetooth is primarily a cable replacement for system. Selecting the appropriate communica- point-to-point connections, and is typically used tions strategy from hard-wired, serial bus, more in consumer environments. Like WiFi, wireless, and other options demands a careful Bluetooth uses higher transmission power and evaluation of the application and, in most cases, requires higher battery power. Typically, a blend of available technologies. batteries life can be measured in weeks. It is Wireless communications can deliver real-time designed to connect short range, inexpensive data transmission, application mobility, and devices and replace cable connection to remote management capabilities. computer peripherals like printers. Bluetooth is part of a group of technologies considered as a wireless personal network (WPAN). ZigBee ZigBee is specified as a low-rate WPAN for supporting simple devices that consume minimal power and typically operate in the personal operating space (POS) of 10 m. It is considered a viable solution for industrial applications with low rate, low power, and short

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