Considerations for Online PdM Systems
A primary consideration for an online monitoring system is to determine which machines warrant surveillance monitoring, compared to what can be accomplished with walkaround (portable) or protection monitoring systems. The figure below provides a good representation of where surveillance monitoring has traditionally fallen in a vibration measurement condition-monitoring program.
As this graph indicates, online surveillance systems are most commonly employed on assets that are costly to maintain and negatively impact production efficiency when out of service. Another key consideration is the anticipated time from the first indication of a developing problem to the actual onset of failure. For instance, if the asset is likely to fail in days or weeks, an online surveillance system is the most cost-effective approach. Studies have shown that an online surveillance system is more cost-effective than walkaround (portable) systems when the required data collection interval is more frequent than every four weeks. Note, however, that a typical surveillance system uses polling and input multiplexing. It is not intended to take the place of a high-speed, quick-reacting protection system with shut-down capability. Another application for online surveillance is represented by the small area on the chart designated as Dangerous or Inaccessible.
Surveillance systems have found widespread use in dangerous and inaccessible locations in a factory environment. Machinery that had been left out of programs in the past due to the expense of manual data acquisition in dangerous and inaccessible locations is now being added to these types of systems. This is primarily due to the attractiveness of the installed cost per point and the ease of installation of surveillance systems.