Condition Monitoring

Wouldn’t it be amazing to be able to see the future and know that a failure is going to occur? A good condition monitoring system can help you get ahead of your failures and fix problems before they become catastrophic.

‘Proactive’ is a management buzzword you hear all too often, but when it comes to maintenance of your plant it is always far better to think ahead and be ready for a failure.

Quality maintenance procedures are of course vital for keeping your equipment up and running, while a well stocked set of spares helps reduce downtime in the event of a failure.

But with condition monitoring, you can analyse how your plant and equipment performs over time and detect problems before they cause plant or process failures.

While your system should already have sensors and switches to check for catastrophic events (over presssure, over temperature, no coolant or lubricant etc.), many people don’t have sensors specific to checking on the condition of their system as a whole.

One of the most common types of failure on a plant is with moving or rotating machinery, and the most effective way of performing condition monitoring on that type of equipment is to install a vibration sensor. Moving machinery always vibrates as it operates, but as it deteriorates, the vibration often becomes more intense. By installing sensors to pick up this vibration and generating alarms when it exceeds normal operating conditions, you are alerted to problems with your equipment well before they reach a critical or failure state.

The graph above shows how you can perform basic condition monitoring by adding a sensor (in this case, a vibration sensor on a piece of moving plant equipment). You can simply set an alarm point (shown by a dotted red line) to either alert maintenance staff or shutdown the system in response to the deteriorating condition of the machine.

It doesn’t just have to be vibration - bearing temperatures, heater output, control response speed and delay, non-linearity etc. can all be monitored in this way. Many of your existing transmitters - particularly HART, Fieldbus and Profibus PA units - already provide diagnostic information that can be valuable for condition monitoring, but very few sites access this valuable information.

On a plant-wide SCADA or control system, you can use recorded historical data to perform a baseline comparison of your process now to your process immediately after construction. Using that information you can determine if your equipment is consuming more energy, running hotter, vibrating more, performing slower or responding differently - all of which can be key indicators of hardware condition deteriorating and efficiency dropping.

With the right SCADA solutions and engineering team, you can even automate this process to perform the comparison in real-time.

The example below shows how you can use existing plant information for condition monitoring. The wide lines show a conrol loop on a gas burner that is used to reach a constant temperature.

The solid lines represent the 'baseline' measurement - a recording we took when we knew the plant was in good condition. The blue lines represent the input signal (the amount of gas that the burner wants) and the green lines show the actual amount of gas being supplied.

The dotted lines represent the current measurement.

By comparing the two (assuming we have compensated for other factors), we can see distinct differences....

The fact that the dotted blue line is significantly higher (we are trying to consume more gas) could indicate that there is a problem with either heat loss (perhaps our insulation has failed) or that our gas quality is low, indicating that there may be a leak in our pipework..

The fact that the dotted green line has changed it's curve shape and the green is taking significantly longer to reach the blue would often indicate a failure in the seals or diaphragm on our control valve..

By perfoming condition monitoring tests, you gain the ability to predict a number of your failures before they occur - giving you ample time to schedule downtime, get in spare parts and compile safe methods of work for the maintenance work that needs to be done. These tests do not have to be obtrusive or difficult - they can be automated and integrated into your existing SCADA system. In fact, monitoring may already be present in your modern control valves and smart hardware, it might just be that you aren't access it yet.

The end result is a plant that is more reliable, more efficient and therefore significantly cheaper in the long term.