HMI Software Powers Diagnostics

The telephone rings. It's midnight, and the plant maintenance foreman is on the line—Op 30 is down again. That's okay. Just boot up the laptop, log on to the company's network via the Internet, and find out what's wrong without leaving home. This vision of the future has come true.But why be awakened at all? What if the operator fixes the machine without calling an engineer because ...

07/01/1999


KEY WORDS

 

  • Human-machine interface

  • Human-machine interface software

  • Software for control

  • Statistical process control


The telephone rings. It's midnight, and the plant maintenance foreman is on the line—Op 30 is down again. That's okay. Just boot up the laptop, log on to the company's network via the Internet, and find out what's wrong without leaving home. This vision of the future has come true.

But why be awakened at all? What if the operator fixes the machine without calling an engineer because the machine dials a pager, shows what is wrong, and then shows how to make repairs? Capabilities in HMI (human-machine interface) software like ActiveX objects, sound card support, video files, and browser support are bringing that picture to life.

The increasing integration of logic, HMI, and the World Wide Web make it easier to monitor and troubleshoot processes. Manufacturers use de facto standards like Microsoft Windows operating system, OPC (OLE for Process Control), COM (Common Object Model), COM+, and DCOM (Distributed COM) for communications, and Microsoft Internet Explorer or Netscape for browsers that are familiar to most programmers and users. Many vendors now build a common database for logic and HMI to decrease errors caused by retyping tag names.

Logic coding diagnostics

It is common in relay ladder logic (RLL) programming to assign a block of words in a file to diagnostics so tags in the HMI software may access it easily. A timer may be set in a line of code. If the code does not execute in the time allotted, there is a fault. The timer done bit will go high, setting a bit in the diagnostic word. The HMI software tag will see the bit change and take action.

Graphic languages provide some obvious places to place these timers. Sequential function chart (SFC) is the graphical organizing "language" of IEC 61131-3, the international programming language standard (see December 1998 CE , p. 42). An SFC consists of steps, actions, and transitions. The code for actions and transitions can be Relay Ladder Diagram (RLD, the IEC's name for RLL), Structured Text, or Instruction List. A Step block is an ideal place for a timer. If the transition code does not go "true," then the timer times out and sets a diagnostic bit. Since the program is in a known place, the diagnostic message can be linked to a message, pointing to a particular part of the machine or process.

Flowchart programming is gaining popularity as a PC-based control language. Part of the reason is many people learn general flowcharting in school, so reading a flowchart program is not entirely foreign. The accompanying example—courtesy of Steeplechase Software (Ann Arbor, Mich.)—shows how flowcharting easily links to diagnostic messaging or HMI software.

Flowcharts, like SFCs, are graphical representations of the program composed of various kinds of blocks Only an action block and a decision block appear in the example. The action block contains code causing a drill to retract. The decision block is waiting for completion of the action. If the proximity switch at the retracted position of the drill is "on" (Retracted_Prox=ON), then the decision is true or "Yes." A timer is initiated with the command to retract with a preset of 3 sec. If the timer times out, the processor looks for other inputs that could be a reason for the fault.

A further action could be to call an HTML page to display, in this case resident on the local PC's hard drive, explaining the fault to an operator. If the PC is on a network, the diagnostic page could reside anywhere on the network.

Graphical diagnostic representation

Tom LeBay, application engineering manager for Xycom Automation (Saline, Mich.), points out that a popular tool for maintenance technicians is to watch the program execute in the SFC view. A mouse click on a stuck block takes the technician directly to the problem code or indicates on which machine area to focus attention.

Another popular tool is a graphical representation of I/O racks showing LEDs flashing. An operator can monitor a situation without opening electrical cabinet doors. Several applications have been designed with process schematic diagrams instead of picture graphics to assist troubleshooters in locating the problem area more quickly.

"Users would like to go to a paperless environment for diagnostics," says Mira Gearhart, engineering vice president at Cutler-Hammer/Eaton (Westerville, O.). "They want to get rid of the notes taped around the machine and sketched contact flow diagrams by putting more power and flexibility in the HMI diagnostics. HMI software can notify those who need to know automatically. Small logic and network analysis tools improve troubleshooting." She confirms the benefits when diagnostics are closely coupled to the logic in flowchart programming.

Closely coupled logic-to-HMI diagnostics is not limited to flowcharting. Schneider Electric's (North Andover, Mass.) Smart Machine Suite contains a patented technique that modifies the PLC logic solver to perform diagnostics by marking rungs of logic and saving data. Alarms and prompt messages forwarded to HMI are logic annotations running in real time and updating automatically. Mike Mellish, vice president, industrial applications group of the Automation Business of Schneider, says, "This software reduces the difficulty and time required to write logic, list variables monitored, detect faults, link these variables to an alarm handler, and create alarm messages. The database is accessible for analysis tools to discern trends and detect processes beginning to go out of tolerance."

Action Monitor, part of Smart Machine Suite, allows an operator drill down into the PLC hardware to log faults. Future designs will expand this function to the sensor level.

Total Control Products' (a subsidiary of GE Fanuc Automation, Melrose Park, Ill.) fXView HMI package is similarly integrated with its fXControl machine-logic software. A common database allows a variable created in fXControl to automatically appear in the HMI. For instance, if a motor alarm or prompt appears on screen, a mouse click will call up associated logic. A Tool Chest allows the development of OLE (Object Linking and Embedding) objects. An object is defined once, then usable several times in logic and HMI. Changes made in the object class are therefore reflected automatically in all applications calling it.

Objects provide flexibility

Object programming continues to grow in popularity and power. Once an object's properties are defined, it can be used in many places. If a change is required, modifications made once remain in effect wherever the object is used in a program. In the Microsoft Windows world, the most common objects are OLE and ActiveX. Libraries of ActiveX objects readily available on the Internet can be dropped into almost any application that accepts them. Objects sets in Sun Microsystems' Java world are called Java Beans. These can also be dropped into any application that accepts objects and typically support more processors than Intel does.

Object-Factory (Greenville, S.C.) has developed logic and HMI applications using Java Beans technology. The HMI is a standard web browser with Java Beans objects. An operator or maintenance technician can create personalized screens by dragging and dropping objects to the browser. In this manner, only the areas of need are viewed in a normal window. Object-Factory also provides a "trace buffer" which contains the last two to three minutes of a machine's run time. A technician can browse to the buffer on a machine failure and review the last minutes of life, literally with the ability to watch how the machine operated through graphic objects. Since this is standard browser technology, it is possible to do this over phone lines from anywhere.

Instead of placing many objects on one screen, DataViews Corp. (Northampton, Mass.) makes the entire screen one object. Long known as a developer of tools for visualization application vendors, its HMI-Go for Visio Technical turns a Visio drawing into an HMI interface. HMI-Go's one object takes less computer overhead and loads more quickly, compared to multiple objects. The HMI-Go object is associated with rules and actions. The rule is in "if...then" logic. Action elements can open files like audio for public address announcements, video, dial pagers, or whatever is necessary for getting information to the right person.

Video also is an option with GE Fanuc Automation's (Charlottesville, Va.) Cimplicity HMI, according to product manager, Craig Thorsland. Cimplicity HMI—the first to be an ActiveX container (a program that accepts ActiveX objects)—incorporates dropped-in sound files that give instructions to operators and delivers live video so operators can observe from a remote location.

A growing diagnostic application is statistical process control (SPC). SPC uses statistics formulas to monitor processes. An operator can know when a process is about to go out of control and make appropriate preventive changes. WebView automatically converts the source screen to the web-standard HTML page so standard browsers can display graphical Cimplicity screens. PocketView, a palm-sized Microsoft Windows CE computer with a version of Cimplicity, monitored controllers over a wireless LAN, during National Manufacturing Week in March.

Trending, preventive diagnostics

SPC and trending have become essential to manufacturing management (see related cover story). Even early HMI software packages had some trending elements. A good database is essential to provide information for analysis. A commonly used relational database is Microsoft's SQL Server. A problem with a SQL database is moving information quickly into it. Wonderware Corp. (Irvine, Calif.) has developed InSQL with DDE servers and compression algorithms to deal with the large and quickly changing amounts of data. InSQL then moves data to Microsoft SQL Server, for analysis in Microsoft Excel or a custom report. This information is also available to business applications driving diagnostic information up to a higher, business level.

Mark Smith, engineering manager of Axis Inc. (Sommerville, N.J.), a Siemens Energy & Automation (Alpharetta, Ga.) integrator, says that alarm logging and management is a basic requirement for diagnostics. He uses Siemens' WinCC to monitor setpoints of various analog inputs. Often monitored points are pressure or temperature, but analog setpoints are valuable even in machining applications. Motor torque can usually be monitored as voltage input. If a drill or milling tool is wearing, torque value will rise. An alarm can trip based on a setpoint determined through experience with the operation. Because WinCC accepts scripting in C, an alarm can be programmed to call another program. For instance, in the drill tool example, an audio file could be called to play over a local PA system or dial-in pager to inform the operator that it is time to change tools.

Rockwell Automation's (Milwaukee, Wis.) Rockwell Software RSView32 was another early ActiveX technology adopter. Recognizing the demand for remote notification, it has added a technology to the core product called Add-On Architecture (AOA). AOA technology enables developers to add applications to integrate with RSView32. First applications with AOA are TrendX, RecipePro, and SPC. Just announced is RSView32 Messenger. Messenger uses alphanumeric pagers, e-mail, fax, sound card, and dialogic telephony cards. With batch applications, it can signal an end-of-batch run. PocketLogix with "RSViewLite" is a palm-sized Windows CE computer providing a mobile diagnostic terminal for operators and technicians. It was demonstrated at Automation Fair and National Manufacturing Week, but was not available for sale as of June 1, 1999.

Audrey Harvey, senior BridgeView architect at National Instruments (NI, Austin, Tex.), says NI has taken its core data acquisition technology and used it with BridgeView HMI to provide diagnostic trending analysis. Using high-speed data acquisition hardware, BridgeView captures data and performs FFT (fast fourier transforms) and other signal analysis. Adding the de facto standard communications driver, OPC, enables BridgeView to publish data for use by other applications. NI has also seen demand for remote notification and supports dial out, World Wide Web interfaces, and paging.

Pushing messages

One annoying thing about using a browser to "surf" for data is that the operator must initiate communications. An important message could be sitting in queue waiting for the "hit." Commercial web companies have addressed that situation and developed push technology. When a subscribed page changes, the server sends it to the subscribing browser. A well-known commercial application is PointCast. Intellution (Norwood, Mass.) has taken this technology to the factory. "iWebCast" pushes relevant data directly to a computer using the customizable PointCast interface.

InduSoft (Hilton Head Island, S.C.) has ported its Windows NT-based HMI to Windows CE. Providing the benefits of instant on, diskless operation, and small devices, CEView provides HMI interface for a variety of SCADA applications. Diagnostic functions include math capability, historical data logging, x-y charts, and trending.

It won't be long until the excuse—"I didn't know about it"—is history. Many creative ways now exist to provide critical machine or process information to those who most need it in a timely manner.






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