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1. General aspects of monitoring and diagnostics.

Question 1.5.

You offer the software for automatic diagnostics of rotating machine units such as bearings, impellers, gear wheels and so on. Are all these units really diagnosed similarly in different types of machines? The question asked by the representatives of the metallurgical plants during the annual meeting of maintenance service managers of metallurgical industry.

The question is answered by Natalia A. Barkova:

The peculiarities of diagnostics of the same units in different machine types certainly exist and they are taking into account in the proposed software. These peculiarities can be divided into three main aspects:

  • by rotation frequency,

  • by machine construction peculiarities,

  • in what stage of the specified operation life the machine or its unit is diagnosed.

So when the diagnostics is made for a machine with rotation speed of several RPM then it is made by middle frequency vibration, but when the rotation speed is about several revolutions per second it is made by low and high frequency vibration.

According to the constructive peculiarities the machines are divided firstly by those where each unit is accessible for vibration measurements and those where many diagnosed units have no access for measurements and the vibration there has to be measured on a significant distance from the optimal control points. In the first case it is possible to diagnose in detail each unit separately, in the second case it is necessary to diagnose a group of units jointly creating a very special diagnostic programs. Such programs are designed and customized for example for some types of aviation engines and certain types of gas pumping machines in gas industry.

By different stage of specified service life the machines are divided on three main groups. The first group includes the machines just after manufacturing (maintenance), not run-in, with possible manufacturing and mounting defects. The second group includes the permanently controlled machines with possible defects of wear that are detected in the incipient stage of development and are watched up to their repair. The third part includes the machines that are diagnosed for the first time before their repair with the aim of flaw detection.

In the first and third cases the standards of unfalty and faulty units are automatically constructed by a group of machines of similar type, and in the third case the possibility of machine dangerous condition appearance is additionally taken into account when the main methods of detailed diagnostics may already not work and give incorrect results.

In the second case the standard of unfalty machine (unit) is automatically constructed on the results of preceding intermittent vibration measurements and the symptoms and defect levels are defined a priori by the results of special diagnostic investigations with the possibility of these levels following corrections. In this case it is possible to achieve the most reliable results.

Its own peculiarities has the transport machine and unit diagnostics. For this type of diagnostics are produced even special diagnostic systems which are often called the stand systems. They have two peculiarities. The first one is the result of limitations on the transport mode of operation during the procedure of diagnostics. It is made not during the transport movement it means not when the transport has the specified optimal revolution rate and loads applied to the diagnosed units. The second peculiarity is in often absence of the data concerning the vibration and noise that could be obtained during periodical measurements. Consequently the diagnostics is usually made according to the rules concerning the flaw detection of the equipment that came for repair, viz. according to the rules for the third group of diagnosed equipment.

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