Virtual Sensors As a Part of the Product Offering

The traditional approach to monitoring the condition of machinery has been to attach physical sensors to the locations that are most fragile or provide the most valuable information about machine performance or condition. These measurements are obtained using physical hardware sensors. Hardware sensor development continues at a rapid pace, and sensor pricing has decreased. Sensors with modest accuracy are cost-efficient. Even sensors with wireless capability are both economical and readily available.

However, hardware sensors are prone to failure, wireless sensors are usually battery operated with limited battery capacity, and wired sensors require direct connection to the data acquisition system.These deficiencies can be overcome by using virtual rather than hardware sensing.To exploit their full capability' and to get accurate measurements, however, the implementation and continuous use of virtual sensors requires another type of engineering expertise above and beyond that needed to implement a hardware-based sensor solution. The following sections introduce the technical background basics needed to enable effective use of virtual sensors and some specific features that are associated with the used methods.

Technical Methods Enabling Virtual Sensing

To use any sort of virtual sensing, one must understand the available and applicable technical methods and tools. There are a handful of methods that have been developed over the years. Some of the simplest methods rely on linear analytic equations, which make them attractive for analyzing simple cases where a linear relationship exists between the measurements and the observed parameter. On the other hand, advances in computational power and the development of more advanced numerical methods make it possible to conduct more detailed studies. The selection of methodology is always a trade-off between computational efficiency and accuracy.

Another significant feature that must be considered when planning to use the virtual sensing approach is if the virtual measurements can be done online or offline. Online calculation means the measurements must be performed in real time, whereas offline measurements means that the measurements are done independently of machine operation, which introduces an opportunity to use more accurate simulation methods since computation time is not a limiting factor. Typically, the most accurate model comprises a combination of different modeling techniques, i.e., analytical equations, numerical solutions, and precalculated parameters. The model used as a virtual counterpart of the physical system can also be included in the product data management system as a part of the product data.

 
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