Although the practical differences between handheld and online condition monitoring (CM) might seem obvious, the way in which each method is used can differ significantly. This article will discuss the common use cases of both handheld and online CM.
Summary of practical differences between handheld and online CM
Simply put, handheld CM involves the use of a handheld sensor, which is applied to a machine when necessary to determine the condition of the machine, and ultimately determine when maintenance must be scheduled.
Online CM requires sensors to be installed permanently (either on the asset itself or near the asset) and provides ongoing real-time insights into the health of the motor.
The handheld CM use case
An important initial point to make is that handheld CM typically offers a less complete picture of asset health, and so is often applied to assets of medium criticality. The reason that it offers a less complete picture is that by definition, readings are taken at intervals instead of continuously. And fewer readings translate into a less precise picture of asset health. If the assets that need to be inspected are far apart, in an ATEX zone, in a hazardous location or in a difficult-to-reach place, then this can result in even fewer readings being taken. Whether this incomplete picture provides appropriate protection against unplanned downtime is determined largely by the criticality of an asset (and the downtime costs associated with that asset), and as such an incomplete picture is typically applied to assets with a medium criticality level.
As well as monitoring assets of medium criticality, handheld CM is also a popular monitoring method for assets that do not run regularly. If an asset only runs half the year (for example, the motor powering a ski lift), then readings may only need to be taken for half of the year. So it may not make financial sense to install permanent online CM on assets that only run periodically (however, this obviously depends on the criticality of the asset when it is running).
The online CM use case
In comparison with handheld CM, online CM provides a much fuller picture of asset health. As online CM involves the use of permanently installed sensors, it is used to automatically take regular measurements from the asset without needing to dispatch an engineer to inspect the asset. This in turn means developing faults can be quickly detected and resolved before unplanned downtime occurs. It follows that online CM is often deployed on high-criticality assets, where preventing unplanned downtime is a priority.
Online CM comes in a number of different forms, and online vibration analysis (VA) and motor current signature analysis (MCSA) are among the most popular forms. Although they are both online, they themselves have different use cases.
For example, online vibration analysis is used to monitor assets located in hospitable environments. This is because vibration-based systems require sensors to be installed on the asset itself. If the asset's environment is particularly hazardous (think about a conveyor in the hot roller table in a steel mill), then the sensors themselves can be damaged, which can disrupt your data flow and could even result in a missed fault alarm.
Conversely, MCSA-based systems are suited to all environments, and excel in situations where assets are located in hazardous environments. MCSA-based systems measure current and voltage signals from within the motor control cabinet, which is a dry and hospitable place for sensor deployment. This means that regardless of the location of the asset, the sensor is able to provide reliable motor measurements without being damaged by the environment around it. And because MCSA typically detects 20-30% more failures when compared to online vibration analysis, it's no wonder that MCSA is the fastest-growing monitoring technology in the industry today.
Which is best for my use case?
To determine the right type of CM for your use case, it's worth discussing your requirements with a CM supplier. If you would like to learn more about the different types of CM in the short term, download the condition monitoring comparison guide.