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Performance (Functional) Diagnostics

If we use technical state monitoring (GOST 20911-89)  as an example, it becomes clear that a 'parameter of a technical component' is a parameter related to its structure (properties of an object or its separate parts, their dimensions).

Operating actions or ambient conditions may initiate the processes (electrical, mechanical, thermal etc.) in a component that transfer the object from one state to another. These conditions are characterized by respective state parameters.

Object sate parameters should not be identified with parameters of the object itself, but the influence of the former will eventually lead to changes in the latter.

If these processes caused by external (operating) actions proceed fast enough as compared to the life of the object under diagnostics, then parameters that characterize these processes in the objects (state parameters) will change fast as well.

The structural parameters (parameters of the object) behave in a rather different way.

A specific feature of the singled out parameter groups (of a conditions or of an object) is related to a time interval during which the processes proceeding in the object under monitoring are considered.

Accordingly, a performance diagnostics system must have the following capabilities to increase the accuracy of the technical diagnosis based on a component:

1. Component monitoring conditions imply minimum time intervals of measurements: interval must tend to zero while control must be carried out in real time/as much close to real time as possible.

2. It is necessary to monitor not only a general level of a unit or a component, but to monitor a vibration level of each component of the unit and a defect characteristic of the component (rolling element, bearing race, separator, lubrication defect, centering, slipping of components, turning in the bearing housing, rotor disbalance, gear engagement defects, loose fastening etc.).

To make it possible, frequency separation of natural frequencies of the unit's components is required. This means that when changes in the amplitudes of frequencies of all elements of a component and frequencies of defects are observed, we can absolutely objectively
monitor each source of emerging vibration, and, respectively, there is no misunderstanding about the source of defect growth and vibration increase and there is no misunderstanding during pinpoint repair of the component.

3. It is necessary to use existing parameters of influence on the component under monitoring (e.g., use existing control systems' data on pressure, current load, voltage unbalance, load distribution, bearing load, roll wrap angle, temperature of bearings and oil, flow, pressure differential/cavitation/pulsation etc.).

In this case, threshold levels are set not as fixed values in accordance with GOST/ISO/VDI only, but they should rather change depending on the applied range of parameters and operating modes of a unit/component. Warning/emergency alarm must actuate based on a bundle of data, on which the unit vibration level depends.

Advantages: Both the operator and the diagnostician always know the real cause of vibration increase. There are no false actuations and ungrounded/ineffective maintenance/emergency works. A diagnostician does not spend much time for a problem justification and is always sure about the provided data.

-      Diagnostics department works approx. 80% more efficient (as statistics indicates).

-      Reduction of costs for maintenance + repair work + spares approximately by 23-28% (as statistics shows).

-      100% transition from a scheduled maintenance program to a condition-based maintenance.

Disadvantages: Diagnostician's human factor is still present and may influence opinions of managers. Also, it is necessary to have an educated and experienced diagnostician.

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