Measuring Ramp Differential Expansion with the SKF VM600 Protection System

As described in application note CM3074, SKF / Vibrometer’s VM600 Machinery Protection System is specifically designed to perform critical measurements that help control large steam turbine generator trains. One of the more important types of these measurements is differential expansion.

Differential expansion monitoring measures change in axial clearances between the machine rotor and the stationary casing. These changes are caused by thermal changes inherent in most machines. The primary purpose of a differential expansion monitor is to guard against 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 common transducer configurations for ramp differential expansion (RDE). Transducer orientation is
considered, along with the appropriate MPC-4 Machinery Protection Card configuration.