While for many machines, machine safety is especially important, monitoring systems should, in addition to the rigorous and extensive requirements of functional safety and SIL certification, provide more features. For operators, the detection and clear identification of the location of the damage site is a top priority. This applies in particular to reciprocating compressors, which have an especially high number of moving parts exposed to continuous reciprocal loads. This challenge is met by condition monitoring systems that incorporate automatic diagnostic functions. The automatic diagnosis does, however, have limits, especially in conjunction with a rapidly executed emergency shutdown.

The very short decision making periods available are necessitated by the need to protect against fast spreading damage and often do not allow time for the longer term diagnosis required to identify possible causes before an emergency shutdown. The exact cause analysis must therefore take place after completion of the emergency shutdown. Based on an analysis of over 400 detected incidences of damage, it is possible to state the following: 30% of all catastrophic damage (e.g. piston rod breakages) that led to an emergency shutdown developed within 120 seconds of a state of normal operation. In the past, the machine was started again in order to detect the damage acoustically, and as such, narrow it down. The consequential damage was generally several times larger than the actual factor triggering the damage.

But after an emergency shutdown at five o‘clock on a Sunday morning, for example, how can damage to the automatically shut down machine be identified? How can one quickly identify whether it was a false shutdown, as is often argued? With its high safety standards, the aviation industry provides the model for the most viable solution with the flight data recorder that has been standard for decades. By integrating ‘voice recorder’ into the machine safety concept, a maintenance technician can reenact the shutdown in the same way as if he has been on the scene at the time. Due to the rapid development of some types of damage, a gapless transient record of as much data as possible is crucial in the post mortem analysis in order not to miss any important elements when securing evidence for understanding the events with regard to the important aspect of damage avoidance. For the reciprocating compressors, in which typical time signal analyses enable diagnoses that are more accurate than the frequency spectrum analyses used with turbomachinery; this means, ideally, the gapless recording of all monitored time signals for each crankshaft revolution before, during and after the event associated with the damage.

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