Internet-Based Distributed

Measurement and Control Applications

ndustries that develop and use distributed measure- ment-and-control (DMC) systems are migrating away from proprietary hardware and software platforms in fa- \'or of open systems and standardized apprmches. Some

of the key components of '1 DMC system are sensors, actua- tors, controllers, and control networks. Large DMC systems

often consist of many sensors and actuators from various manufacturers and multiple sensors or control networks sup- plied by differellt \renders. Component interfacing and sys- tem integration are major issues that require significant efforts from multiple dxsciplines with technical backgrounds. Thus, standardized trmsclucer (sc'I1sc)r and actuator) interfaces,

June 1999 IEEE Instrumentation & Measurement Magazine 1094-6969/99/$10.00019991EEE

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high-level programming languages, object-oriented plat- forms, and intranet and Internet technologies serve to shape the next-generation DMC landscape. They all are key to eas- ing system integration. This article describes a framework for standardized DMC integration and a demonstration June 1999dhering to the framework designed at the National Insti- tute of Standards and Technology (NIST).

Based on our effort, we have found three major areas where open standards will play a critical role in future DMC development processes. These areas are:

B Transducer interfaces B Open network communications B Distributed application development

rk Fig. 1 illustrates the distributed control framework for an in- dustrial automation environment. Information and data sup- plied by sensors in the process connection level-the lowest level in the control hierarchy-are sent to the control network nodes where distributed intelligence can be executed. Sensor data received by the processors in the network nodes is broad- cast onto the network. Other nodes in the network use the sen- sor information to make control decisions that manipulate the actuators or communicate with other nodes. Closed-loop con- trol may occur either at an individual network node or among multiple nodes. Distributed control schemes allow decisions to be made in the process level in a distributed manner based on simple commands from the enterprise applications.

This distributed framework has less network traffic than the traditional centralized control design. Also, computing is distributed over the entire system, as opposed to being cen- tralized in the traditional manner. Status is reported to the ap- plication and enterprise levels for system-type control, condition-based monitoring, diagnostic, or database archiv- ing. In order to provide an environment that supports interoperability as shown in Fig. 1, a framework for standard-

ization must be included in the overall distributed measurement and control design.

We describe a demonstration project using this NET, Internet-based DMC framework in the following sections. The hardware, software, and standards used during the develop- ment are described. The standards used to implement the con- nectivity of transducers to the network nodes are also addressed. We next focus on how Ethernet is used as a control network me- dium, and we describe the software NIST developed to support open-network communications. Finally, we describe the soft- ware used to implement the distributed control applications on both the network nodes as well as in the client.

At the lowest level of a distributed measurement and control hierarchy, sensors and actuators are needed to sense environ- mental conditions and control physical entities, respectively. Transducer interfacing refers to the process of physically and electrically connecting the transducer to a microprocessor in the network node. A key reason for standardizing the interface at the hardware interconnection level is the current compatibil- ity problems transducer manufacturers face when integrating their devices into multi-vendor networks [l], [2], [3].

Transducer interfacing also requires standard software in- terfaces to provide application and network interoperability at the network nodes. Because the network and the transducer must expo:;e their interfaces directly to transducer applica- tions on each node, any attempt to migrate the application, the sensor hardware, or the network node to another platform re- quires a time-consuming and costly redesign of the applica- tion’s interface to the new environment.

When standard interfaces such as IEEE P1451 are used in the DMC or any closed-loop manufacturing system, sen- sor-to-sensor interchangeability and sensor-to-network interoperability can be realized. Some of the key features of the IEEE P1451 smart transducer interfaces are that the stan- dards specify digital c

Enterprise Level Enterprise i~~~ Transaction Amlications . . Process Mapping Specifications

Application Level

- ~ ~ ~ ~ - ~ ~ I CORBA, DCCM Application Frameworks L . .

Distributed Intelligence Level *---* iL%VC_i*W

IEEE P1451 1

Process Connection Level IEEE 1451 2

Fig. I . Industrial automation framework.

24 IEEE Instrumentation & Measurement Magazine

nmunication protocols from sensor to network, and self-identification of sensor. This means that a sensor can describe itself to the network, facilitating an automatic system configuration. The 1451-based sen- sors or actuators achieve self- identification via a memory chip physically attached to the sensor. The chip stores information such as manufacturer name, identification number, type of device, and serial number, as well as calibration data. This information is called the trans- ducer electronic data sheet (TEDS). The TEDS can upload to the system upon power up or upon request. The incorporation of IEEE 1451 standards into transducer hard- ware will simplify the tasks of sen-

June 1999

To Machine

Location of Transducers

Fig. 2. The components of the DMC system.

sor and device maintenance by enabling simple "plug and play" for replacement and upgrade. The TEDS also serves as documentation. Over time, this electronic documentation is more accurate and cost-effective than traditional paper docu- mentation methods.

Transducer networking is similar to networking the personal computer (PC). There is a network-capable application proces- sor (NCAP), equivalent to a small computer, that resides in ev- ery transducer network node or control network node. An NCAP could be an 8-bit microprocessor for a DeviceNet control network, or a 32-bit microprocessor for an Ethemet-based con- trol network. Presently, many DMC-based control networks use proprietary hardware and software interfaces that limit the availability of data to higher-level networks and repositories. Ethernet has long been established as a data communication network used widely in office and factory automation.

The use of Ethernet as the preferred medium for DMC-based control networks is rapidly gaining in momentum due to its speed, cost-effectiveness, and the ability to leverage off-the-shelf application components to facilitate building dis- tributed systems [4]. Changes in the IEEE 802 Ethernet specifi- cation are making Ethernet quite powerful as a network for device-level control. For example, the IEEE 802.1~ standard for message prioritization or quality of service (QoS) was initially developed for streaming live video, audio, and other multime- dia content. Indeed, those in the control-network arena can le- verage the real-time deterministic capabilities in the Ethemet standard. The standard effectively guarantees that messages can be delivered and/or acknowledged in less than 4 ms. This range is within most tolerances for providing adequate response times for process-control applications.

Opponents of using Ethernet as a control-network me- dium have argued that Ethernet will never be deterministic enough for real-time, closed-loop control applications. How- ever, Hewlett-Packard (HP) engineers have recently shown that timing in many critical applications can be maintained to an accuracy of better than 500 ns using Ethernet as the control network [5]. Also, the Foundation FieldBus organization has selected Ethernet for their control network draft specifica- tions. The FieldBus specifications define an H2 network,

which is a standard for higher-speed networks with data rates around 100 megabits per second (Mbps) [6]. High-speed Ethernet was chosen above several other competing propri- etary buses.

An implementation at NET based on the DMC framework merges the newly emerging IEEE 1451 smart transducer inter- face standards and the de facto networking standards from the Internet community to remotely monitor and control an industrial process via the Internet. State-of-the-art hardware and software technology for DMC deployment is described in terms of a real-world, Internet-based application. The specific scenario addressed in the NIST DMC demonstration project is as follows. In the NIST machine shop, a high-speed, precision milling machine is used as the testbed. During the millingpro- cess, a means of maintaining a relatively constant temperature of the material is required. Large temperature differentials in an open machme shop environment can result in dimensional variation of the finished parts. A coolant tank, shown in Fig. 2, serves as the coolant source to the part being milled.

We designed an Internet-based, DMC closed-loop control system to regulate the temperature in the coolant tank. Fig. 2 illustrates the mechanical components of the DMC-based con- trol system. The goal is to keep the coolant in the tank within a specified temperature range. During the machining, the cool- ant temperature tends to rise due to the heat generated in the cutting process. The increase in ambient air temperature around the machine also contributes to the rise in coolant tem- perature. A chiller maintains a reservoir of cold water that is constantly circulated. The coolant from the chiller is directed into the coolant tank when demanded, via a three-way valve. Through this control process, a consistent coolant tempera- ture will be maintained in the coolant tank throughout the part-machining cycle.

The goal of the NET Internet-based DMC demonstration project was to provide a means, via standardized interfaces, to access, view, monitor, and control this DMC application in real time. In order to provide this capability, several key hard- ware and software technologies were developed. The overall NIST DMC demonstration project topology is shown in Fig. 3. A Java applet shown in Fig. 4 executes from within a web browser like Internet Explorer 4.0 or Netscape Communicator 4.5.' It provides an information delivery mechanism to the shop floor or operation manager's desk across the country. Any web browser that supports Java can be used to view this application. A web server located at NIST provides the Java and hypertext markup language (HTML) data file repository capabilities for the browser in this demonstration. The actual DMC system was developed using two, state-of-the-art, HP Ethernet-based, prototype network nodes.

These nodes support a reference implementation of emerg- ing IEEE P1451 specifications that provide standardized ap- plication programming interfa& (API) to the transducer and the network, and standardized hardware interfaces for con-

June 1999 IEEE Instrumentation &? Measurement Magazine 25

+ I Ethernet Control Network 8

I 60 Temperature Sensors @Valve Actuator

Fig. 3. The overall Internet-based DMC demonstration topology

Fig. 4. Remote monitoring and control applet

necting transducers at the digital level to the Ethernet nodes [7], [SI. The temperature sensors and the valve actuator were

all directly controlled in this distributed settink using C lan- guage applications developed at NIST for the embedded Ethernet-based P1451 compatible HP nodes. Higher-level dis- tributed control and monitoring capabilities were imple- mented in the Java programming language.

The nodes communicate information between themselves us- ing a TCP/IP publish-subscribe messaging protocol. The messaging technology dows a node to publish a topic, a specific piece of information in ASCII string, for example, "node2.sen- sor.funktemp," which represents the temperature in the coolant tank, on the network. Another node would subscribe to this topic to re- ceive updates on the temperature of the tank. The HP nodes shown in Fig. 3 were programmed to provide many other services. These services can be controlled and monitored via the web-based Java client applets. The Java applets do not communicate directly with the Hp nodes. The applets must connect with a NIST-developed TCP/IP gateway to request services from the nodes.

Fig. 4 illustrates the NIST-developed Java applet for re- mote monitoring and control using the Microsoft Internet Ex- plorer 4.01 browser. This demonstration was featured at the 1451 booth at the International Society for Measurement and Control (ISA) Expo98 exhibition in Houston, TX, October

1998. This application can also be viewed at: http://ino- tion.aptd.nist.gov/P1451 /ISADemo.htm.

The research conducted on the Internet-based DMC project in- fluences several other areas of research in other NIST labora- tories. One of these is the collaborative research project conducted between NIST and other national measurement in- stitutes (NhLIs) in North, Central, and South America. Its goal is to significantly reduce the amount of time it takes to per- form a complete round robin of international comparisons of measurement standards. NIST is finding ways to reduce this time by leveraging Internet technology.

This pilot project, involving 12 participating member countries of the Inter-American System of Metrology (SIM) and dubbed "SIMnet," has just been demonstrated at NIST. The SIMnet system, shown in Fig. 5, effectively provides an Internet-based environment for real-time comparisons of elec- trical calibration measurements among 12 participating SIM countries. NIST's focus in the SIMnet effort is to use the Internet to provide real-time audio, video, data, and applica- tion-sharing capabilities. This system allows the metrologists of the 12 NMIs collaborating in real time to perform compari- sons of electrical measurements, calibration procedures, and measurement data of digital multimeters (DMMs). Through the use of SIMnet, we expect to shorten a round robin of inter- national comparisons of electrical measurement standards for the DMMs from three years to six months.

In another research study, NIST scientists are using DMC research results to incorporate telepresence technology into calibrating gas flowmeters. In order to expand their flowmeter calibration capacity without spending millions of dollars to build a new facility, flow measurement scientists at NIST have set up a project and collaboration agreement with the Colo- rado Engineering Experiment Station Inc. (CEESI) to use its

Fig. 5. SlMnet provides an Internet-based environment for real-time comparisons of electrical calibration measurements among 12 participating SIM countries.

26 IEEE Instrumentation & Measurement Magazine June 1999

via simple plug-and-play sensor and actuator components. In addition, using standardized components and interfaces will certainly reduce interoperability problems.

[l] N. R. Johnson, ”Building plug-and-play networked smart transducers,” Sensors Magazine, Oct. 1997, pp. 40-61.

[Z] K. Lee and R. Schneeman, “A Standardized Approach for Transducer Interfacing: Implementing IEEE-P1451 Smart Transducer Interface Draft Standards,” Proc. of Sensors Conference, Philadelphia, PA, Oct. 22-24,1996, pp. 87-100.

[3] R. Schneeman, and K. Lee, “Multi-Network Access to IEEE P1451 Smart Sensor Information Using World Wide Web Technology,” Proc. Sensors Conference, Boston, MA, May 13-15,1997, pp. 15-34.

Automation Research Corporation. Oct. 1997, pp. 1-31.

the fieldbus,” ISA Tech/97, Anaheim, CA., Oct. 7-9,1997.

networks,” InTech Magazine, Apr. 1998, p. 18.

Actuators Network Capable Application Processor (NCAP) Information Model, IEEE P1451.1 D1.83, Dec. 16,1996.

Actuators-Transducer to Microprocessor Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats, IEEE Std 1451.2-1997, Sept. 26,1997.

[9] P.I. Espina, ”Tele-metrology: remote flowmeter calibration,” Flow Control, vol. 5, no. 1, Jan. 1999, pp. 16-21.

[4] Automation Strategies: Ethernet-based Control Network Strategies,

[5] J.C. Eidson, and W. Cole, “Closed-loop control using Ethernet as

[6] B. Baranski, and J. Strothman, “Ethernet picked for FieldBus’ H2

[7] Draft Standard for a Smart Transducer Interfacefor Sensors and

[8] Standardfor a Smart Transducer lntevface for Sensors and

E DisclaimerXertain commercial products, hardware, and software are identified in this article in order to de- scribe the system. Such identification does not imply recommendation or endorsement by the National In- stitute of Standards and Technology, nor does it imply that the products identified are necessarily the best or the only one available for the purpose.

Fig. 6. A large flowmeter calibration facility at GEES1

large-flow calibration facility. This project will use the 1451 smart transducer interface technology coupled with the ap- plet-based Internet techniques developed at NIST to remotely monitor and control the calibration process of gas flowmeters at CEESI, with flow rate up to 3.95 standard liters per minute (slm) [9]. NET scientists will use real-time video, audio, and computer means through the Internet to remotely check the health of the sensors and equipment before and after the cali- bration, coordinate the calibration procedures with the remote staff, control the collection of calibration data, monitor the measurement results, and coordinate sending the measure- ment data back to NIST for computation and validation. A typical, large-scale, outdoor pipeline setting for flowmeter calibration at CEESI is shown in Fig. 6. This project is currently in the design phase, with a small-scale model already demon- strated in a recent workshop held at NIST.

U m ma ry In summary, the NIST DMC demonstration project that has been described here spans all levels of the DMC system. This multilevel data communication capability is a viable one as a result of standardized networks, protocols, and transducer in- terfaces. Common Intemet-based software technology was used to provide the ease of data migration between the various communication pathways. Standard and de facto software lan- guages such as C and Java were used with off-the-shelf devel- opment tools to implement the embedded network node applications and the web-based application, respectively. Intemet-based TCP/IP protocols and Ethernet technology were used to design the networking infrastructure.

The distributed measurement and control concept with networking sensors and actuators should work quite well with advanced system design, particularly where sen- sor-based monitoring and control applications are important. Taking this approach in system design can reduce the total life-cycle cost of the system by use of modular sensor system design and commercially available smart transducers with standardized interfaces, and easy maintenance and upgrade

Kang Lee is Leader of the Sensor Integration Group at the National Institute of Standards and Technology (NIST). He is also is the Chairman of TC9, I E E E Instrumentation and Measurement Soci- ety‘s Technical Committee on Sensor Technology. Currently he is coordinating an effort in industry to establish a set of I E E E stan- dards, A Smart Transducer Interface for Sensors and Actuators, to ease the connectivity of sensors to systems and networks. He received his B.S.E.E.from the Johns Hopkins University and M.S.E.E.from the University of Maryland. Rick Schneeman is a Computer Scien- tist in the Manufacturing Engineering Laboratory at NIST. He is also a member of the Automated Production Technology Division. He is a inember of one of TC9’s four working groups, which has re- cently developed a draft specifcation for a smart transducer infor- mation model, I E E E P1451.1. He received his B.S. in Computer Science and Information Systems Management from the University of Maryland and M.S. from the Johns Hopkins University.

June 1999 IEEE Instrumentation & Measurement Magazine 27