HOW TO – Preventative Maintenance Procedure for Control Systems

These days automation is deeply entrenched in nearly all industrial equipment. The automation may be overly simplistic or complex, but at the end of the day, it is a computer system controlling a process via variable speed motors, heaters, and other processing machinery. The computer makes its decision based on multiple sensors located around the machine, many of which you probably can’t see.

Even the simplest of automation systems have the potential to negatively impact a machine’s reliability significantly. When a control system does breakdown, the key to minimizing the losses relies heavily on correctly identifying the problem and understanding how to fix it.

Rom-Control established over 14 years ago to diagnose and repair all makes and types of industrial control systems and we have seen it all through our doors. We are experts at Root Cause Analysis and the repair of even the most complex industrial control system, from simple night lights to aviation, petrochemical, primary industry, and transport, etc, we have seen it all. We can help you set up an appropriate preventative maintenance procedure specifically aimed to maintain your control systems.

Preventive Audit and Maintenance Program

General preventative maintenance programs are considered standard practice in most industries but nearly all do not address any form of control system inspections or audit. Developing a focussed preventative maintenance procedure aimed at your equipment’s control system should prevent nearly all associated unplanned downtime and delays. The appropriate rectification of these faults will also eliminate secondary and follow-on faults usually caused by the small first discrete failure.

As a minimum, the checks should include the following at regular intervals;

  1. test and replace all failed indicator lights, alarms, buzzers, horns, bells, etc.
  2. clean and test cooling fans, filters and heat sinks
  3. ensure BIOS and machine default parameters haven’t changed
  4. fine-tuning and adjustment
  5. re-calibration of sensors and detectors
  6. predefined part replacements
  7. Check power supplies and test for under and over voltages.

Of significant importance is item ‘a’ as many system faults may not be realized if a warning light or a buzzer has malfunctioned, and the operator is not aware. Checking and testing will ensure the machine’s warning systems will provide adequate indication before a serious and usually expensive breakdown occurs.

Look for Abnormal Conditions.

You cannot know if conditions are abnormal unless you know the normal process parameters for your system. These are the normal operating ranges of temperatures, pressure, levels, flows, and leak rates, etc. Refer to the process documentation, operation and maintenance manuals, balance report, as-built drawings, commissioning report, and previous maintenance logs and records to determine the operational range, and at what value alarms will initiate.

Be on the lookout for unusual operating parameters that are not monitored by the control system. If you are aware and are alert to these warning signs, you can often circumvent a breakdown by making simple changes that will stop the occurrence of a major fault.

Finding Faults

Even with routine audits and the best preventative measures, your system may fail and you should be prepared for it. If the inevitable happens, we suggest a high level approach to diagnosis as per the following procedure.

Reproducible Faults

If the fault is reproducible then your task is relatively easy. You will also want to understand how repeatable it is. For example, when the fault can be reproduced, does it occur every time or only sometimes? If it occurs always then you go into the diagnostic mode to try to find the problem.

Intermittent Faults

Intermittent faults that seem to occur randomly and you cannot reproduce them easily are some of the most difficult problems to troubleshoot and rectify in a control system. While they may still be repeatable infrequently, it may not be easy to locate the fault, as the factors responsible for that repeatability are either outside your control or hidden from your view.

How to Fix the Problem?

Regardless of the issues that a control system might present, the following methods can assist in identifying the problem. Once the problem is identified and isolated, then the remediation will more reliable.

Isolate the Problem

Most control systems consist of a complex array of electronic components and sub-assemblies all working together and when a fault occurs, it could be caused by any one of those components and sub-assemblies or the communications between them. If you are unsure of the root cause of the fault, then list the symptoms and determine a testing regime to isolate the cause. For example, you may consider replacing a sensor with a functioning spare and if the problem still exists, then the original sensor is likely to be functioning properly and proceed further with the next replacement test and so on until you isolate the root cause.

Trial And Error

For the trial and error method, it is important to only change one parameter (eg sensor) at a time otherwise the results can be confusing. Be sure to document the change and record the result with each trial. The trial-and-error method works best for issues that can be repeated easily. If a trial with multiple changes resolves the issue, then you can independently test the two or three changes to determine the root cause.

Check Logs

Computer log files are a good place to begin troubleshooting a control system. Many PLCs can also log data points and create trend charts on the fly. For intermittent issues, if possible set a separate independent data logger that gives a snapshot of the parameters when the fault occurs. This will provide vital clues for identifying the fault.

What Happened Before the Fault?

It is an obvious step to consider the events before the fault occurred but it is often overlooked when stresses are high and the machine needs to be fixed. Almost always the answer to this question will uncover the cause and type of the problem. Always come back to this question when identifying the cause of faulting equipment.

Talk to Your Experienced Plant Operators

I am sure many of your plant operators have worked with the same equipment for years and have enough experience on their hands to be a great resource of information. Use them. They can provide a lot of practical and on the spot information and may be able to tell:

  • Was the system or equipment operating beyond its normal parameters
  • Condition in the field at the time of occurrence of the fault
  • If someone has come and changed anything or done any maintenance
  • Explain the machine’s tendencies and quirks
  • Recent changes in the product line, materials, or settings
  • any environmental changes such as dust  or heating

After a long investigation, a fault may still be difficult to identify. Trying to isolate the fault using the trial and error method can often become confusing and the information difficult to process. This is a good time to talk to others knowledgeable about the machine such as the operators and maintenance staff to discuss what you have done and the results you have found. Being one step back means others can review the situation and suggest other solutions that you may not have seen.

Use the Product manuals and Documentation

If you don’t have the technical manual on-hand, look it up online. It’s simple, but a fundamental step in finding out more about the faulting equipment. At a bare minimum, keep these resources stored with the machine, so they’re available to the maintenance staff or external control system technicians.

Use Online Forums

There is a huge amount of information available on-line. There are forums and groups which discuss problems and solutions related to control systems. This information is freely available, although you have to be a little bit skeptical about its authenticity, nevertheless, it is a great resource for getting fresh ideas. Use it.

Finally, Keep an Open Mind

While you are trying to locate the fault there may be some aspect of the problem that you initially misunderstood and, in turn, could inhibit you from exploring other possibilities.  When you reach such a stage that you feel that you are at the end of the road with no other options, then move back and reassess the problem from the beginning. Removing an incorrect assumption made early in your diagnosis can make all the difference. You have to be methodical in your approach to troubleshooting which can reduce the time and effort to find the root cause of the problem and find a solution.

In closing……

Control Systems can be simple or complex but all can breakdown without notice. The result can mean loss of production, high stress and ultimately finanical loss.  Most organisations have implemented Preventative Maintenance Programs but many either neglect the control system and the sensors and control mechanisms as this is considered a “black art”. If you need assistance in what an appropriate Preventative Maintenance Program is for specific control systems, Rom-Control can assist as our many years of experience in this field will identify the key checks and tests which can be completed quickly. Depending on the situation, the frequency of checks may be daily, weekly or even monthly and should be considered an audit, which means documented proof the check was completed.

For a discussion or assistance with developing your Control System Preventative Maintenance Program, you can contact us at or ring 1300 766 287.