IO module replacements: Intelligent marshalling, integrated networking

I/O wiring can be among the most challenging of upgrades. When replacing input/output connections, what are key considerations? Thad Frost, manager, research, development and engineering, Invensys Operations Management, offered answers.


Invensys 247 FBM fits into the standard base plate of its I/A Series DCS and can be programmed with software to manage most standard I/O combinations. Courtesy: Invensys and Paul Maggetti of Maggetti Digital MediaWhen replacing input/output connections, what are key considerations? Thad Frost, manager, research, development and engineering, Invensys Operations Management, offered answers. If you don’t want to replace field wiring, also read: “IO module replacement without disturbing field wiring.”

Control Engineering: I/O wiring can be among the most challenging of upgrades. When replacing input/output connections, what are key considerations?

Thad Frost, manager, research, development and engineering, Invensys Operations Management: Because lifting and changing field wiring can be very expensive, the first consideration would be to determine whether the field wiring can be preserved and to choose a vendor that can assure that you can do that. (See related articles.) If new wiring is needed, it should be installed in a way that provides flexibility to change signal types without disturbing the connections again. New intelligent marshalling functionality from Invensys makes it possible to change signal type through software. A 4-20 ma signal can be changed to a HART signal, for example, with a few keystrokes.

What functionality do attached applications need to incorporate?

As technology evolves and plant environments strive continually to do more with less, there is an increasing need to gather more data via the field wiring, for example, to use bus technology. The Invensys intelligent marshalling functionality that is now part of its I/A Series distributed control system is a good example.

What types of signals (analog, digital, serial, mixed...), what units (current, volts, resistance, ac, dc...), what range, and how many channels are needed? What network protocols are required, and will they be wired, wireless, serial, digital, or a combination?

Intelligent marshalling allows incorporation of all types of signals. Vast combinations of signal types can be landed on one I/O card. Baseplate-mountable termination assembly increases I/O cabinet density immensely.

What are the sensing, signal conditioning, distributed control, isolation, and other requirements? Will the application expand, and by how much?

Expansion is constant based on the demand for more data from the field instruments. The functionality of some field instruments has evolved into the equivalent of what were once called minicomputers.

What design and how granular should the modules be?

Intelligent marshalling modules should be universal in nature, allowing a wide variety of signals to be mixed and matched at the I/O card level. These points should able to be changed at the software level so that no cabinet is ever reopened or no wired lifted.

Will the I/O connections be enclosed or exposed?

In an intelligent marshalling configuration, the I/O connections will be enclosed.

What are among the most-overlooked considerations?

By eliminating the dependency on marshalling cabinets, intelligent marshalling will reduce equipment and footprint costs, and provide savings in documentation, inventory, and field labor. In the process industries, marshalling cabinets are used to collect field wires coming in from various devices throughout the plant. Once wired, these field wires are then rerouted to the DCS terminations. Historically, this has been done to segregate the DCS wiring from the field wiring. With intelligent marshalling this physical marshalling process is no longer necessary.

- Thad Frost, manager, research, development and engineering, Invensys Operations Management, and Mark T. Hoske, CFE Media, Control Engineering,

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