Oil Analysis Alarm Limits
One of the most important ways to have a successful machine health analysis program is to take action on the data you receive from your lab. There are a few different ways to go about determining alarm limits, as well as whether you should look for static or trending limits.
Our goal at TestOil is to pinpoint that spot when a machine condition goes into alarm. This can be a marginal or critical rating. Once the machine goes into alarm, that is when we trigger analytical Ferrography to take a second look.
Some labs use a static element based on the machine type. So, if it's a gearbox, if it's a hydraulic system, if it's a compressor, you have a fixed limit for wear metal.
Statistical Method of Linear Regression
TestOil uses a statistical method of linear regression, where we're looking at a trend over time and predicting where the two and three standard deviation points are, which would trigger a marginal and critical.
Take industrial gearboxes, for example; some labs will set an iron and copper limit at a certain level. You can have a gearbox that typically sheds iron at 15 to 20 parts per million, and then another gearbox that sheds iron at 250 to 300 parts per million.
Because they're both industrial gearboxes, they're going to have the same static limit of 100 PPM.
The one that's shedding iron at a lot lower level is never going to get flagged at 100 PPM, but if it went from 20 to 50 parts per million, that should be getting flagged, and it would work with the static limit.
The one that's a much higher level is always going to get flagged above 100 PPM. And it probably isn't the case until it gets to 400-500 parts per million.
Learn More About Alarm Limits
If you do want to find out more about whether static limits are linear regression type trending limits are a better fit for you, you can always go ahead and download our eBook, Get The Picture.