How to Increase the Integrity of Your 4-20mA Loop

An integrated group energy company recently suffered two plant shutdowns in a row tied to plant wiring.  After the first one, they inspected every potential point that could have contributed to the failure including changing IO boards, instrumentation and power supplies, only to have the situation reoccur.  After additional troubleshooting measures, it was discovered that over time, a short circuit occurred in the wiring to two critical pressure transmitters.  It turns out that this type of failure happens frequently within the process industries.  The first indication something is wrong is typically when an operator notices the measurement is not reading as expected.

Troubleshooting a 4-20mA loop can require extensive investigation.  Issues can occur in the wiring, the power supply or any component within the loop itself. Wiring that was perfect upon installation will degrade over time due to effects of challenging environmental conditions or unintentional human interaction. One troubleshooting guide published on-line includes up to 32 potential causes with almost as many test procedures needed to verify the cause.  This type of troubleshooting is done on a reactive basis and requires that someone is aware an issue might exist.

There is a better way to increase the integrity of your 4-20mA loop.  By implementing on-line diagnostics, maintenance practices can move from reactive to proactive.  Loop Integrity diagnostics, which are available with Rosemount 3051S and Rosemount 3051 pressure transmitters, continuously monitor the loop in order to detect abnormal conditions such as:

  • Damaged or corroded wiring
  • Water build-up due to condensation
  • Deteriorating power supplies
  • Ground loops or electrical shorts

A world-class petrochemical manufacturer located in Houston, Texas was experiencing intermittent device failures related to “overheating” of the wiring in conduit.  Wiring was replaced, but the situation persisted.  It got to the point where unit shutdown was being considered.  Luckily, the site was using Rosemount 3051S transmitters with the Advanced Diagnostic package and Loop Integrity diagnostics were easily enabled.  The diagnostics detected the presence of a floating ground.  Unit shutdown was avoided, saving the plant over $3.6M in estimated costs. 

In a similar fashion, the integrated group energy company decided to upgrade their critical pressure measurements to include Loop Integrity diagnostics.  Now both plants get proactive notification when abnormal loop conditions occur. This helps them pinpoint the source of trouble and take corrective action before it impacts their operation. Rosemount Loop Integrity diagnostics are on the job 24 hours per day 7 days per week, minimizing the need to do manual loop checks by a qualified technician. Rather than spending time troubleshooting elusive wiring issues, the focus at both facilities has moved to improving operations due to the increased uptime and availability.

Find out more by watching the video below or visiting our website.

Loop Integrity Diagnostic - Rosemount 3051S Pressure Transmitter