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5 Measuring Oil Quality
5.1 Introduction
There are a number of ways to describe oil wear and oil condition:
Tan Delta Number (TDN)
Loss Factor Percentage
5.2 Tan Delta Number
To make it easier to monitor and trend the overall oil condition, regardless of your current
method, we have introduced the “Tan Delta Number” (TDN). The TDN has been designed to be
easy to understand, to give a very good level of accuracy and to create a common language for
describing overall oil wear and oil condition, which can also be combined with other methods
such as ISO cleanliness levels and laboratory test results.
The full scale goes from 1200 to 0, with the value decreasing as oil quality degrades. For most
applications, the useable range is from 1050 to 300.
5.3 Oil Degradation
It is important to understand that oil degradation is exponential and your use of Tan Delta
products should reflect this. Once the TDN begins to fall at an increasing rate you know the oil
is nearing the end of its life and you need to be vigilant. To help with this, our Display Express
has Check, Alert, and OLR functions to alert you to any potential issues.
Figure 2 - Typical Oil Degradation Curve
5.4 TDN Value vs Loss Factor Percentage
The underlying value which the sensor is recording for the oil condition is the Loss Factor
Percentage which is then converted into a TDN value as shown in
Appendix (Section 14).