Fieldbus on the Cheap? (don’t do it!)

In a recent issue of Control magazine,  January 2009, an article appeared, “Fieldbus on a Shoestring”. In this article, the author proposes using wire you have on-hand for use as the fieldbus network cable in order to save on cost. If anything is a formula for trouble, this is.

You can read the article here:

http://www.controlglobal.com/articles/2009/FieldbusShoestring0901.html

Here is our response:

(this was a letter sent to the editor of Control magazine)

“Dear Mr. Montague:

In the recent article “Fieldbus on a Shoestring,” John Rezabek suggested a risky proposition: cutting corners during the economic recession by using nonstandard cable for fieldbus applications. He cited tests he’d seen in which non-fieldbus cable performed in a fieldbus lab situation.

Then Rezabek takes a leap-assuming that a cable that performs in a cozy lab setting will perform similarly in the field, where electrical noise, temperature extremes, chemical, moisture and UV exposure are inevitable and unpredictable.

Rezabek purports that it’s worth taking the gamble that the cable will perform. He suggests that you can replace it later, when the economy improves. Or address deficiencies if and when they arise as long as “your projects and business demands will tolerate a little back-pedaling.”

In today’s precarious economy and job market, is that a gamble you are willing to take? Can you afford to take responsibility for a plant’s significant downtime, while the source of the problem is investigated?

Rezabek proposes designing risk into your projects. Many engineering, manufacturing and industrial cable experts would agree that’s not a smart gamble.

An improperly designed, implemented and installed physical layer is the Achilles’ heel during start-up and commissioning. One problematic segment can throw the whole network into a tailspin. It is more cost-effective to use the proper tools from the outset. Also, consider how relatively inexpensive material is compared to the cost of labor.

ISA-SP-50 specification defined Type A cable with precise requirements, while Type B and Type C cables had progressively looser specifications. Types B and C cables and the resulting difficulties in real-world conditions prompted the Fieldbus Foundation to replace the problematic ISA specification with the new FF-844 specification, which eliminated unsuitable Types B and C cables to ensure reliability and uptime now and in the future.

Look at it this way. Choosing cable other than that specifically designed for fieldbus applications is like using diluted antifreeze in a new truck in Wisconsin. It’ll be OK in the fall, but it won’t be pretty in December when temperatures drop well below zero.
It’s a costly risk for very little cost savings.

You probably would not be willing to rely on a nonstandard product for your new vehicle. Why would you consider it for industrial networking projects? Designing the physical layer on the cheap is not truly economical.

British author and social commentator John Ruskin (1810-1900) wrote:

“It’s unwise to pay too much, but it’s worse to pay too little. When you pay too much, you lose a little-that is all. When you pay too little, you sometimes lose everything because the thing you bought was incapable of doing the job it was bought to do. The common law of business balance prohibits paying too little and getting a lot. It can’t be done. If you deal with the lowest bidder, it is well to add something for the risk you run, and if you do that, you will have enough to pay for something better.”

Rezabek said, “In times of hardship, I’ve been known to compromise.” Part of the challenge of the recession is not simply to cut costs now but to work smarter, to reengineer and redesign the way you work so you are more efficient for the long term. Looking only at the short term is shortsighted. Rolling the dice with what you have, as Rezabek suggests, is taking unnecessary chances with your company’s productivity and potentially your job.

Northwire and other reputable, service-oriented cable manufacturers strongly advocate meeting customers’ requirements and the Lean principle of perfect first-time quality. The insignificant cost difference between standard cable and fieldbus is not worth the risk.

No one knows when the economic recession will end. Therefore, we all need to step up efforts to reduce waste, but not at the risk of creating potential crises.

Product manager
Northwire, Inc.
Osceola, Wis.”