Find The True Culprit
EP Editorial Staff | March 1, 2022
A system approach to troubleshooting will help you get past the assumed cause of asset failure.
By Matt Asbill, Motion
Modern cars have a “check engine” light as a catch-all indicator that something needs attention. Your local auto repair shop connects to the car’s service port to retrieve a code that specifies the problem. Most industrial equipment and processes don’t provide that same type of information. Thus, maintenance personnel must use their knowledge and experience to determine what to do next. Typically, that determination is accompanied by an enormous amount of pressure to quickly fix the problem and get the machine back online.
Plants that invest in predictive-maintenance programs will decrease the time required to find the root cause and return to normal operation. Imagine a plant floor that maintains a regular vibration-analysis schedule for gearboxes and motors. If a VFD or starter begins to trip out on random faults, this will minimize the total number of items to check for the source. Properly aligning v-belts or couplings using laser tools typically means there is no need to evaluate them for vibration or current spikes. Bearings that are correctly greased and maintained will mean that shafts, tooling, and related parts will turn freely and true—again, allowing the troubleshooter to check other places.
A predictive-maintenance program aims to decrease or potentially even stop unexpected breakdowns. Although not every single component of a complex machine can be analyzed and studied for possible signs of failure, you can expect that the process of elimination will greatly contribute to quickly finding the culprit.
Some of the best clues to a problem’s source can be obtained from operators. Suppose the machine ran fine for years with product A but introducing product B led to headaches. In that case, you may conclude that the original machine design was limited in scope and not meant to operate on anything but the initial parameters. Or perhaps the production department recently decided to increase output by simply speeding up the machine. Instead of trying to determine why the VFDs are suddenly giving over-current trips, maybe it just requires slowing the machine back down to standard operation.
Start by asking the operators when this issue first appeared and if the machine operated smoothly before then. An operator may have noticed a specific sound or vibration that wasn’t present before.
Keep in mind that each person will diagnose the problem based on their background and existing knowledge of the process. Was the maintenance department notified about a broken part? Has an electrician been resetting continual VFD trips?
Early in the fact-finding mission, there will be various inputs about the importance of the corrective action and how to expedite it. Downtime is not productive for anyone, from production supervisors to the management. However, it’s vital to understand that a temporary fix may lead to more problems down the road, not to mention that safety should never be compromised. If the PLC or VFD program must be modified or tweaked, make sure that you have hard copies of all the original parameters. This will help return the machine to normal operation if some other component impairs performance.
Before making changes for testing, turn off the machine (for safety) and take notes and pictures of the existing wiring and related parts. The wiring may have been replaced or modified over the years and not reflect the original prints. See if the machine will run at any speed or on any type of product. This may give you a baseline to test for stability and proper operation. These steps will make it possible to return to a known starting point.
Instead of focusing on the most likely suspect, ask yourself what other factors may be contributing to the problem. Collect and study drawings and wiring diagrams to see what field component types are connected. A bad encoder on a vector motor could cause a current overload trip on a VFD instead of high amps. Dirty or misaligned sensors may affect light-curtain operation or show false detections. Almost every device that triggers an alarm or experiences random issues may be pointing you in a different direction. Mechanics will want to blame motors and electricians will point at gearboxes, primarily because they’re not as familiar with the devices.
Once enough data has been collected to point toward a specific component, replacement is only the first step. If a bad bearing in a gearbox has led to a motor failure, installing a new motor is just a temporary fix.
Slowly bring the machine back online to see if the original complaint has been addressed and corrected, while watching for introduction of another issue. Being patient is also important because parts need to heat up and run for extended periods before showing signs of stress or conditions that may or may not be related to the original issue.
Think of a machine as a system, not a bunch of individual parts. Parts are all usually interconnected in some way, either directly or indirectly. Not taking the time to consider the impact each component may have on others will force the troubleshooter down a rabbit hole with only a single focus. Save your original notes and observations and summarize how the issue was corrected. Depending on the plant’s protocol, this may mean asking engineering personnel to change existing prints or the storeroom to identify a higher-quality bearing or motor.
Finally, explain to the operator what was found and what steps were taken to remedy it. Operators are frequently left out of the maintenance repair phases, even though they may provide the most accurate depictions of where to start looking for a problem. If they feel included in the process, they are more likely to notice when the machine has deviated from normal operation in the future, often before a catastrophic failure occurs. EP
Matt Asbill has been an Automation Specialist at Motion, Birmingham, AL (motion.com), for 27 years. He worked on government, aerospace, and military projects for six years prior. Asbill holds a B.S. in Electronic Technology from Missouri State Univ., Springfield, and an M.S. in Engineering Technology from Pittsburg State Univ., Pittsburg, KS. For more information, visit Motion.com/efficientplant.