David Matherly
Yokogawa Corp of America

With so many flowmeters now offering digital communication options, such as HART and Fieldbus, how should these features be factored into the flowmeter selection process? How can an end-user best determine if such features are and/or will be relevant for their application now or in the future?

Practically all manufacturers of electronic flowmetering instruments offer some type of digital communications in addition to their standard analog outputs. For end-users that have not yet embraced the use of digital communications, a wise first step is to begin utilizing HART communications because of its availability and proven legacy within the process control industry. HART communications is easily understood and applied and actually operates over the same two wires that are already carrying the current (milliamp) analog signal to the end-user’s computer/DCS/PLC/controller. With this additional digital signal, manufacturer’s flowmeters now offer so much more information than the traditional, analog process variable signal provides. Additional process data, meter health, and diagnostic information are just a few additional variables available through digital communications. Adding HART communications to a control system can be relatively easy. A HART module can usually be added to a PLC’s I/O bay or utilized within most controllers so that the additional information offered can be realized.

Experienced HART communication users sometimes decide to migrate to purely digital forms of communication and control, particularly when upgrades or new installations take place within their process plants. Not all flowmeter manufacturers offer these types of digital communication platforms instead of the traditional analog signals. The end-user needs to be careful when deciding to upgrade to a digital protocol (for many reasons). The future needs of the process should dictate this migration path.

While purely digital forms of communications such as Modbus, DeviceNet, and Ethernet have been around for many years, control topologies such as Foundation Fieldbus and Profibus are relatively new (15 yrs). While adoption of Fieldbus in particular has been slow and industry-focused at times, wider acceptance is assured as manufacturers make their digital flowmeters easier to use. Both Fieldbus and HART technologies are still evolving and improving and will be around for a long time. There is no danger of either technology becoming obsolete anytime in the near future.

The response to this question was provided by David Matherly, product manager of Advanced Product Solutions with Yokogawa Corporation of America. He holds a bachelor’s degree in Applied Science from Arizona State University in Engineering Technology and an associate’s degree in Applied Science from New River Community College in Instrumentation Technology. Mr. Matherly can be contacted via email at: david.matherly@us.yokogawa.com.