Most of the time, facilities have condition-monitoring devices set up. Most of the time, they're still learning of the problem when it's already happened.
This space between these two statements has a name – it is called the "P-F Interval". And being aware of it is what separates proactive from reactive condition-monitoring systems.
What Is Condition Monitoring?
Condition Monitoring refers to the constant or periodic evaluation of the operational status of an asset. Instead of regularly changing the part based on time, Condition Monitoring will rely on actual performance indicators such as vibrations, temperature, electrical current flow, and lubrication status in order to determine whether the machine is in good condition, deteriorating, or nearing failure.
The purpose is not to detect when failure happens. The objective is to detect its coming so that steps can be taken prior to that eventuality happening.
What Is the P-F Interval?
Understanding of the P-F Interval concept is very important for all practitioners of reliability engineering. This is the time period which exists between two points on the failure curve of the asset in question:
P – the point where a potential fault becomes identifiable by means of condition monitoring;
F – the point of functional failure when the asset fails to fulfill the function it should perform.
Thus, the period between P and F is the moment of opportunity for you. When it comes to failure of rolling element bearings, you have 4 to 8 weeks to detect the fault, order the spare parts, plan the maintenance and make a repair according to your schedule.
The lack of condition monitoring system capable of detecting the fault at point P leads to the absence of such a possibility, and F becomes the first sign of trouble.
👉 Learn how Epsum Labs can help: Explore Our Solutions
Why Most Facilities Miss the P-F Interval
There are three reasons why most of the detection windows go undetected.
First, infrequent inspection intervals. An instrument with a 4-week P-F interval cannot afford monthly inspections because this will mean irregular coverage, even if inspections take place regularly. In case of shorter P-F intervals, there will never be any window detected from regular inspection methods.
Second, data latency. Data collected using a portable vibration analyser will become obsolete by the time when they are analyzed, trended, and escalated; hence, no action can be taken in narrow P-F intervals.
Third, threshold only alarm settings. Setting alarms on function failure severity levels only ensures that you detect failures. What you need is to ensure that the equipment does not reach such stages through degradation monitoring.
The Role of Vibration Monitoring in Early Fault Detection
Monitoring for vibrations has been identified as the most efficient means of identifying faults early on during the monitoring of rotating equipment. Mechanical fault mechanisms such as bearings, imbalance, misalignment, and gears always create specific frequency patterns weeks before generating any heat or producing noticeable symptoms.
An example of such a situation would be the case where there was a fault in the outer race of the bearing. In this case, there would be a recurring impulse that is identifiable through its specific frequency pattern. This is point P of the P-F interval.
How Condition Monitoring Supports Predictive Maintenance
Predictive Maintenance requires condition monitoring in order to work. Condition monitoring provides the asset health information. The asset health information recognizes the degradation occurring within the P-F Interval. This recognition leads to the triggering event for the predictive maintenance schedule.
Consequently, the intervention that takes place is both proven to be needed as well as done before its time – installing a replacement bearing before functional failure occurs based upon the knowledge of a known fault progression, versus scheduled or failed bearings.
Is Your Operation Inside the P-F Interval?
If you can't answer these questions without making a phone call or opening up your spreadsheet, you have a gap that is alive today.
- Which asset is nearing failure in your plant right now?
- What's your real OEE for the week, as measured by your machine?
- Which of your fleet vehicles has a fault code that you haven't seen before?
These are the systems that Epsum Labs provides to answer them.
