Manufacturing and production plant systems offer engineers endless opportunities for problem solving, both in system design and day-to-day operation. This is because no single element of a system remains perfect. Everything is dynamic, and a goodly percentage of the movement is in the wrong direction. This is where diagnostics come in. Problems have causes, and the aim of diagnosis is to identify causes. Nail the cause and you are well on the way to nailing the problem.

And this, in turn, is where the diagnostic capabilities built into smart Hart and Foundation Fieldbus instruments apply. Hart is a communication technology and standard promulgated by the Hart Communication Foundation ( hartcomm.org), while Foundation Fieldbus is a network developed and promulgated by the Fieldbus Foundation ( www.fieldbus.org) . Every supplier of bus-system-ready instruments offers versions that are capable of focused and detailed diagnostics, and these diagnostic subsystems are eagerly harnessed by end users—or are they?

A recent Automation World survey indicates that many engineers do not use the diagnostics offered to them. The survey, less about statistics than opinions, revealed that of the 60 identifiable Hart and Foundation Fieldbus users, about half use the available digital diagnostics.

“Diagnostics” does need some definition. It is a market-positive word and like most market-positive words, manufacturers apply it to a variety of capabilities. “Smart diagnostics,” which is relevant here, goes beyond device- and device-transmitter health. It is more than simple feedback that a device is open or closed or pushed or pulled when receiving a control signal. Advanced diagnostics is the sophisticated feedback and monitoring that can be built into a device. In other words, for a valve we mean flow rates, pressure, temperature and the like, not simply that the actuator fired and the valve is open or closed.

Actual diagnostic capabilities can be a complex mix that is dependent on the device type and the manufacturer. The Hart Foundation’s Application Guide puts it about as succinctly as possible:

“Hart instruments can implement extensive, device-specific diagnostics. The amount and type of diagnostic information is determined by the manufacturer and varies with product and application. Diagnostic information can be accessed using the Hart Communication Protocol. Host applications using DD [device description] files can interpret and display diagnostic information. Applications not using DD technology may require product-specific software modules to interpret diagnostic information.”

Here is the key question: Why have virtually half of users opted out of using smart diagnostics? One common answer: lack of integration with other devices. Other reasons include:
 

• the lack of trained personnel to implement and manage or interpret the diagnostics;
• lack of input/output on legacy distributed control systems (DCS);
• the need for additional software and systems; and
• related costs.

Integration issues

There was a fair amount of top-down approaches implied in some of the answers. Among these: “No [we don’t use the diagnostics because] they are difficult to integrate into a broader network.” “No, [because we] need to connect to other standards.” Even the yea-sayers recognize issues around data silos: “In general, yes [we use diagnostics] although the diagnostics are difficult to move into databases and other control systems.”

ON THE WEB: Hart Communication in Action
Read why Wisconsin Energy Corp. (WE) won the Hart Innovative Achievement Award. WE integrated Hart into its maintenance procedures and device configuration.
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Broader networks, other standards, challenges moving data: It is heartening to see users embrace this kind of systems approach, one that says there is a need to look at several devices to see a broader picture than that which is available in a single instrument.

Unfortunately, the richer the diagnostic potential in each device, the more potential there is for complexity in the process of interconnecting them. As one respondent put it, “The large quantity of diagnostics in devices does create issues with what to use, and [affects] the cost/value ratio in the selection. In most plant applications, there is no need to use any diagnostics…. [There are] only a very small number of installation points where they really add value over the cost to implement, monitor and action the outcomes.”

The toughest aspect of engineering is simplifying—in this case, paring down to the essential few devices whose data should be mined in detail—and the larger the system, the longer will be the discussion around what to monitor fully. But, as the same respondent wrote, “The real point is, if you are not going to action them, then they are a wasted cost.”
Lack of trained personnel ...