Experts worldwide agree – the only way to ensure safe, reliable, efficient, economical operation of reciprocating compressors is to monitor them continuously and take appropriate action based on the information the monitoring systems provide.

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That simple objective, however, is difficult to put into practice. The variety of instruments, systems, and methodologies for machine monitoring and diagnostics can be perplexing. Descriptions and claims are sometimes similar, sometimes conflicting, and almost always confusing.

To help provide clarity for your decision process, we offer this plain-language guide to system selection. It lists the essential capabilities a system should have and explains why those capabilities are needed.

This is the culmination of more than 20 years of experience in developing and applying monitoring and diagnostics systems around the world. We sincerely hope our depth of experience will be of assistance to you as you evaluate and implement a system for your operation.


Why It Matters: Systems should be scalable in two ways. First, they should be functionally scalable, allowing new or additional capabilities, such as measuring loops, to be added to an installed system without inordinate cost or difficulty. Second, systems should be scalable in magnitude. In other words, a system should offer a means to expand monitoring to additional machines.

Scalability allows you to take advantage of new developments and keep your system state-of-the-art. As your needs change and your experience with a system grows, you will likely wish to extend coverage to other machines. A truly scalable system provides a simple, cost-efficient pathway for growth.

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 Automated Diagnoses & Messaging

Why It Matters: Detecting the presence of an anomalyis one thing. Defining and pinpointing it is another. Your monitoring system should not only warn you about problems, but also provide an accurate diagnosis with specific component identification, location, and indication of the extent of damage. Armed with this information, you can make wellfounded decisions about the maintenance procedures you need to take and when you need to take them.

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Detecting Failures in Early Stages

Why It Matters: The days of time-based maintenance are over. State-of-the-art monitoring  technology gives you the ability to apply condition-based maintenance, reliably detecting developing failures and intervening before breakdowns have an opportunity to occur. Early failure detection prevents machine damage, enhances safety, avoids unplanned machinery shutdowns, and reduces costs of operation. Success depends on the ability to accurately identify mechanical defects at an early stage – regardless of operating conditions – without issuing false alarms.

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Measurement of Phased Data

Why It Matters: The most important and well established technique for machine monitoring is vibration analysis. However, not all vibration analyses are the same. Seemingly minor differences in data acquisition and evaluation strategies can have a dramatic impact on the quality of signal diagnoses. Choosing the proper mathematical evaluation method is the key to reliable early failure detection and machine protection.

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Life Cycle Partnership

Why It Matters: No monitoring system user should be left alone. The importance and complexity of a full-function monitoring system require ongoing support from your vendor so you can exploit the full benefits of the system and maximize your Return On investment. The support you receive should come in the form of training and assistance to help you fully utilize your system, as well as in continuous product development to keep your system state-of-the-art for the longest possible time span.

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Field Experience

Why It Matters: A reliable, full-featured monitoring system requires a solid number of installations and many years of field experience. No amount of  “laboratory“ testing can duplicate the conditions of one actual operating environment – much less the characteristics of many different operating environments over extended periods of time. What assurance do you have that your monitoring system will perform as promised? How confident are you in the accuracy of the diagnoses your system generates.

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Performance Optimization

Why It Matters: The benefits of optimal compressor performance are clear: improved operating efficiency, reduced energy  consumption and increased productivity. Tracking performance can also provide other benefits, such as early warning of impending gas leakages. Unfortunately, losses in efficiency often go undetected by many monitoring systems that focus on vibration, piston position and temperature only. Machine efficiency – like other key parameters – should be monitored continuously.

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Relevant SIL Certification

Why It Matters: It is important to understand what SIL certification means – and what it does not mean. SIL (Safety Integrity Level) ratings were established to define a metric for evaluating a system’s level of operational reliability with regard to safety, as defined by IEC 61508. As it applies to machine monitoring systems, a SIL rating refers to the probability of failure on demand of the protection system. A key point to remember is that SIL ratings have nothing to do with monitoring precision, which is represented by false trips and missed detects. Keep in mind that, before a SIL rated protection system comes into play, operators have to determine the appropriate SIL rating for the machinery that has to be protected. In other words, IEC 61508 is a risk-based standard and, in order to apply it, criteria for the tolerability of risks must be established for the machine, e.g. a HAZOP study must be carried out (Hazard and Operability).

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Operating Condition Recognition & Threshold Adjustment

Why It Matters: The enduring popularity of reciprocating compressors is due in part to their flexibility. Their ability to handle different loads, speeds, volumes, and gases makes them a favorite for operators – and a nightmare for failure detection modules in online condition monitoring systems. The reason is that varying operating conditions often result in dynamic changes of machine behavior – for example, the vibration fingerprint. Detection of these operating condition changes and the alignment of the threshold setting in parallel can be extremely complex and – if not done properly – will lead to inaccurate results.

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Rod Position Monitoring

Why It Matters: Rod position analysis is more than just an indication of wear. The most effective  monitoring systems incorporate rod position measurement in conjunction with analyses of other parameters to identify impending failures in drive train integrity. Rod position is a valuable analysis that provides alarms and warnings about two major concerns. First, as a dynamic signal for safety protection tasks, it identifies problems with the mechanical machine integrity – such as drive train status, loose connections, overload conditions, and more.

Second, rod position analysis serves as an indicator of wear, especially of piston rider rings. The machine may then be shut down to ensure protection and to perform maintenance before serious damage occurs to the rod, piston, or cylinder.

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Data Recording & Replay

Why It Matters: Even the most sophisticated online condition monitoring systems can perform a protection shutdown of a machine without leaving enough descriptive details to pinpoint the root cause. What option does the operator have? Restarting the machine for more evidence risks catastrophic damage. Exploratory maintenance wastes time, money, and productivity.

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Monitoring System Independence

Why It Matters: Your monitoring system vendor should share your goals for safety, efficiency, cost reduction, and environmental compliance. They should have no competing business objectives that might influence machinery health assessment results, system development, or technical support.

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