Complementary Differential Expansion Measurements with the SKF Multilog On-line Protection System DMx

As described in Differential Expansion application note number CM3073 EN, the SKF Multilog On-line System DMx (a distributed vibration based machinery protection and condition monitoring system) is specifically designed to perform critical measurements used in the control of large steam turbine generator trains. Perhaps the most important measurement is differential expansion.

Differential expansion monitoring measures the change in axial clearances between the machine rotor and stationary casing caused by thermal changes inherent in most machines. The primary purpose of such monitoring is to prevent axial rub between rotating and stationary parts, the consequences of which can be catastrophic.

There are many configurations for measuring differential expansion. This application note discusses the common sensor configuration of Complementary Differential Expansion (abbreviated to “CDE” or “Comp Diff Exp”) which is considered together with the appropriate SKF Multilog DMx channels setup and configuration.