How Reliable is Traditional Wired I/O?

Last year Emerson celebrated the 10-year anniversary of the launch of industrial wireless technology.  While the benefits of wireless are well known and understood, some have yet to adopt the technology due to a perceived fear that wireless is unreliable.  We’ve all experienced the frustration of a dropped call with our mobile phones or having a wi-fi network go down when you are counting on it to be there.  And while the robustness of industrial wireless technology has been well documented and proven, our day-to-day experiences with consumer wireless products can negatively influence the perceived reliability of industrial wireless technology.  But is it really fair to compare industrial wireless with consumer wireless, or would it be more appropriate to compare the reliability of industrial wireless relative to conventional wired / 4-20 schemes that are the vast majority of today’s automation architecture? 

I had some interesting revelations about this topic by sheer accident at the recent Emerson Global Users Exchange in San Antonio, TX.  One morning I ate breakfast with a process engineer from a US pulp and paper facility.  He talked about how he’d love to get some wireless installed, but he was unable to get his organization to overcome their skepticism on the reliability of wireless communication.  Out of curiosity, I asked him how often his wired I/O has reliability issues.  He responded without hesitation: “Oh, all the time.”  Interesting. 

Later that week I was drawn to a presentation that had a catchy title about saving millions of dollars in cost avoidance due to the ability to detect some type of on-scale failure.   It turns out that this was a chemical refinery that was having major challenges with wiring.  The communication on multiple transmitters kept failing, which was impacting their SIS system and the availability of the entire unit.  Wiring was completely pulled and replaced, yet the issue was not resolved.  If root cause was not identified, the unit was at risk for an unplanned shutdown which would take a minimum of three days to turnaround.  Luckily the site was using Rosemount 3051S Pressure Transmitters with the Advanced Diagnostics package, which includes the ability to monitor the integrity of the electrical loop.  They enabled the Loop Integrity Diagnostic, which immediately tripped an alert that notified they were having changing voltage levels at the transmitter.  This prompted the team to troubleshoot the power supply of the control system, and they found that improperly installed grounding jumpers were the root cause of the loop communication issues.   The savings from avoiding the shutdown were estimated at over $3 million.  

To summarize, there is a lot that can indeed go wrong with traditional wired I/O: cables, conduit, power supplies, junction boxes, grounding, electrical interference, and more.  The good news is that you have options.  One easy path is to take advantage of the Loop Integrity diagnostic that is available on instruments like the Rosemount 3051S Pressure Transmitter.  This diagnostic will continuously monitor the loop for fluctuations in voltage and resistance and will notify you if you have an issue.  Another option is to give Wireless another look.  In many instances Wireless can meet or exceed their wired counterparts in terms of reliability.  

How common are wiring issues at your sites?

1 Reply

  • Must have been the session "On-scale Failure Detection Delivers 36 Million Cost Avoidance in Dehydro Unit" (session 2-161840). It reminds me of this article and video:

    The problem with 4-20 mA, which is analog, is that there is no diagnostics to detect on-scale failure. Analog is hard to diagnose. Since there is no diagnostics there is no error message or alarm if the signal is distorted so you get a false sense of it being reliable (correct) while it is not. This is why signals must have diagnostics so you know if the data is good or not