# Diagnosing the Machine Set Rotor Using Its Relative Vibrations
## 1 Introduction  
In industrial, transport and energy systems, the machine set as the driving machine-driven machine subsystem can be distinguished. High efficiency and high dependability of such subsystems is in demand in the management of the enterprise asset. The required efficiency and dependability values can be saved and even increased by using appropriate maintenance methods and means, including appropriate diagnostic methods and means. It is apparent from the available literature that in modern industrial, transport and energy systems, much attention is devoted to the consumption of energy. Models of energy management and energy saving strategies have been created [1, 2]. There are many diagnosed objects as well as methods and means of diagnosing an object [3, 4, 5, 6]. The terms condition monitoring and diagnostics of machines are in use [7]. Tests with the use of vibration methods are conducted on rotating and non-rotating elements, and methods of vibration measurement are determined in ISO 7919-1 and ISO 10816-1 standards [8, 9]. In the literature, the \"machine set\" is not listed as a diagnosing object. In machine diagnostics, vibration methods have proven their usefulness and are therefore widely used. However, mainly rotating machines are diagnosed. The diagnosis of reciprocating machines with the use of vibration methods is small. According to the author, increasing the quality of maintenance is possible by dividing the diagnosed object into functional units, replacing the concept of condition with the concept of wear margin and creating methods and means of diagnosing a given functional unit [10, 11]. The author's earlier research substantiates the thesis that in the machine set, it is advisable to specify the machine set rotor as a functional unit and to comprehensively use relative vibrations as diagnostic symptoms. The efficiency and dependability of the machine set depends on the energy efficiency and reliability of the functional units of the machine set. The wear margin of each functionalunit is created during the production and assembly. The wear margin is determined by the measure values of features of free and built-in components, operating fluids, movement and load of components in operation. The wear margin becomes exhausted during the use of the machine set due to irreversible wear. Wear intensity is not the same for all functional units of the machine set. The functional unit with exhausted wear margin cannot perform its functions with the required quality or may suddenly fail to operate, which in many cases means the failure of the whole machine set. Therefore, it is necessary to restore the wear margin of the given functional unit in advance. From the economic viewpoint, it is justified to restore the wear margin of only those functional units whose wear margin has been exhausted and for which maintenance will be, to a large extent, separately performed. The information on the wear margin comes from diagnosing a given functional unit. The basis for diagnosing functional units are diagnostic models describing the relationships between wear margin measures and diagnostic symptoms measures. The aim of the article is to justify the separation of the machine set rotor as a functional unit of the machine set and to demonstrate the possibility of diagnosing such a functional unit by means of non-contact measurements of its relative vibrations. The investigation will focus on the rotor with slide bearing and crankshaft. It is necessary to present a model of machine set rotor, process-dependent forces and moments acting on the rotor, and forces and moments dependent on the wear of the machine set elements. The wear margin measures of radial and axial slide bearings and measures of the machine set rotor shaft alignment should also be demonstrated. Considerations should include diagnostic relationships between the wear margin measures and vibration symptoms, as well as problems related to non-contact measurements of relative vibration of the rotor.