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Implemented with off-the-shelf technology
By Sree Swarna Gutta
Vibration monitoring and other high-end measurement technologies can solve equipment health challenges that are shaking up the engineering world. Beyond constant change from advances in Industrial Internet of Things (IIoT) and Industry 4.0 concepts, controls engineers are seeing workforce shortages as experienced engineers retire faster than new ones enter the field. Over their careers, veteran engineers became incredibly familiar with how machines in their factories worked. They could touch or listen to machines to gauge performance and whether maintenance was required, for example, on a bearing. However, this depended on the engineer being in the plant and near the machine when it acted up, which is not the most reliable maintenance strategy. In the past, vibration monitoring was accomplished with specialized analyzers, but now can be done with off-the-shelf programmable logic controller (PLC) modules and software using open high-speed Ethernet communications.
New system-integrated vibration monitoring options capitalize on advanced networking technologies with built-in diagnostic capabilities, such as EtherCAT, to improve predictive maintenance. These technologies not only help ease the strain of labor shortages by maximizing each engineer's time, but they also make plants more productive. In the past, only stand-alone black box options existed for these applications, but now measurement modules are available as part of standard I/O and control systems. These technologies use the same engineering environment as the machine control logic, communicate over an open fieldbus, and typically have lower price points than single-purpose hardware platforms.
By leveraging vibration monitoring, plants can quickly identify problems that would otherwise go unnoticed until equipment breaks, so repairs can be handled when the factory or line has scheduled downtime or at least is less busy. This minimizes unplanned downtime and helps engineers proactively fix issues before they affect other machine components. Beyond maintenance efforts, vibration monitoring benefits most applications that have complex motion or require precise measurements. This encompasses everything from improving the accuracy of weight-filling machines in the packaging industry to condition monitoring for a wide range of applications including machines, processes equipment, and wind turbines.
No matter the application, the core principles of high-end measurement remain the same. These include fast communication that is independent of PLC cycle time for extreme accuracy, modules with a carefully designed form factor, and the option to add other measurement technologies that monitor different aspects of machine health. At the most basic level, vibration monitoring systems must be able to read data from sensors, filter out useless data, and analyze the remaining data to determine overall equipment conditions or to correct settings for more accurate weighing.
How to manage all the sensor data
High-end measurement I/O modules gather vibration data in different ways. Depending on the various parameters that they monitor, this could require IP 67-rated modules that can attach directly to a machine or robot in the field. Some machine-mountable options connect to external sensors, while others have built-in accelerometers. This simplifies the retrofit process for machines to include vibration monitoring. Other applications could require modules housed in the control cabinet that gather data from integrated electronics piezo-electric (IEPE) sensors commonly used for vibration analysis. DIN rail-mountable measurement terminals can connect with all other kinds of standard I/O and embedded PC-based controllers via a shared backplane.
Whether mounted in cabinets or directly on machines, the I/O components should provide electromagnetic compatibility (EMC) protection and durability for tough production environments. Metal housings can be beneficial for many applications, because they are more stable and dissipate heat more effectively, which is important in control cabinets. Having a wide selection of connectors, including push-in, LEMO (fiber optic connector), and BNC (Bayonet Neill-Concelman), among others, increases the I/O system's ability to connect to diverse field devices.
Most importantly, vibration monitoring components are now available as open solutions that readily integrate into the existing machine control system. Data transmission, filtering, and analysis are all easier and more effective in open architectures, whether the individual modules connect to the machine controller via an Ethernet cable or a shared backplane. Stand-alone black box devices that need single purpose software and separate mounting are notoriously ill-suited for connectivity with control systems and other industrial platforms. However, EtherCAT-based measurement technology provides a suitable measurement platform, and the system-integrated approach to hardware has maximum flexibility and scalability across a machine or plant.
Vibration monitoring I/O modules capitalize on advanced networking technologies with built-in diagnostic capabilities such as EtherCAT to improve predictive maintenance.
Open deterministic high-speed networking
System-integrated vibration monitoring provides granular data despite extreme conditions. Some modules, for example, have measurement accuracy of 100 ppm at 23°C and 24-bit resolution with up to 50,000 samples per second. As a result, corrective action can be initiated by even the smallest changes in performance, and predictable errors are limited even across long machine lines through low temperature drift.
The speed and accuracy of this high-end measurement technology can be leveraged using a high-performance open standard network such as EtherCAT. Vibration measurement and other forms of monitoring can be successfully deployed with the core elements built into EtherCAT, specifically diagnostics, distributed clocks, oversampling, and timestamps.
- Diagnostics: The EtherCAT protocol has cyclic and acyclic diagnostics. This makes it possible to correct errors rapidly and analyze intermittent issues in depth. In addition, diagnostics integrated into all EtherCAT I/O devices can monitor for cable breakage, short circuits, overheating and over-range, among other issues, and display status through LED lights on the terminals. EtherCAT-based measurement modules ensure the highest quality process data.
- Distributed clocks: The local clock built into every EtherCAT device synchronizes automatically and continuously with every other distributed clock on a network using a standard time base. As a result, precise synchronization of less than 1µs is possible among all devices, while compensating for the varying run times and limiting deviation between clocks to less than 100 nanoseconds. Both deterministic actual value acquisition and deterministic set value output achieve the absolute minimum response times through the benefits of distributed clocks.
- Oversampling: Transmitting process data to the controller more than once per communication cycle is possible through built-in oversampling functionality. Local distributed clocks trigger this useful functionality within EtherCAT measurement, enabling repeated sampling of process data by a set factor within a communication cycle. This achieves higher resolution and numerous other functions, such as fast loop control and fast signal monitoring within a dynamic machine control system. As a result, measurement modules can achieve 200-kHz sampling rates even with moderate communication cycle times.
- Timestamps: With vibration monitoring and other types of high-end measurement, data types contain timestamps in addition to user data. It is possible to pinpoint exactly when and where incidents occur with maximum precision, such as unusual vibration due to worn bearings. Using timestamps, precise outputs can be triggered independent of PLC cycle time.
Timestamps, oversampling, distributed clocks, and diagnostics are fundamental aspects of EtherCAT devices, and they are foundational components of highly effective vibration monitoring.
Eliminate useless data with filtering
It is important to have as much actionable data as possible, which requires eliminating bad or irrelevant data. Some anomalies in the data are not necessarily cause for corrective action but are instead simple mechanical quirks or random spikes that do not indicate a serious, recurring issue. As a result, filtering is a necessary step between data acquisition and analysis. Rather than sending all data to the cloud or a database to be sorted and analyzed, filtering can occur at the field device level. This is a more efficient and cost-effective way to manage data throughput to the cloud or database.
Engineers should select available vibration monitoring modules that have built-in filters with multiple options. These filters, which can include infinite impulse response up to the sixth order, finite impulse response up to the 39th order, or self-defined filters using coefficients, should be configurable via standard control software. This makes the process more accessible to engineers of all backgrounds, because the filters are integrated into the same platform as the engineering environment for machine control. Control engineers can also change filters on the I/O modules at any point during run time to fine-tune the application.
High-end measurement terminals should also have the option to create custom filters with a graphical interface. Butterworth, Chebyshev, and Inverse-Chebyshev are examples of customizable filters, and the filter types include low pass, high pass, band pass, and band stop. Using PC-based automation software, users design the filters graphically and transfer them to the I/O terminals. These system-integrated tools require no changes to the software or hardware.
Example of a system-integrated approach for analyzing vibration monitoring data using Beckhoff TwinCAT automation software and Microsoft Visual Studio charting tools for a graphical representation of signals down to the single µs range.
Analytics enhance vibration monitoring
There are many options for data analysis after useless information has been filtered out. Engineers can use powerful software oscilloscopes in the PC-based automation software for machine control and filter design. This supports seamless integration of existing machine visualization alongside the vibration monitoring data. Some oscilloscope software supports graphical display of data in YT, XY, or bar charts. This option should offer trigger-controlled data, printout functionality, and long-term recordings to support data monitoring over an extended time.
Database servers enable data exchange between databases and the automation software. Direct values from EtherCAT measurement modules log cyclically to the database server, and engineers can analyze the data from the database. Database servers can interact with a library of IEC 61131-3 object-oriented extensions, which enables the creation of code that is highly structured and simple to extend. As a result, command processing performance increases significantly.
Some measurement software platforms also possess condition-monitoring libraries. Analyzing measured values, such as vibration, is simple with a vast compilation of mathematical algorithms in the libraries. A wide range of software modules can suit the requirements of specific measurement and monitoring applications. These libraries support machine vibration evaluation that is implemented according to DIN ISO 10816 (the mechanical vibration standard that provides specific guidance for assessing the severity of radial vibration measured on the bearing housings of industrial machines). Combining multiple algorithms can create a solution for monitoring bearings, precise weigh scales, or other moving components.
The highest level of data analysis requires advanced analytics in edge- or cloud-computing architectures. PC-based controllers send data from the measurement modules to an analytics workbench with standard cloud communication protocols, such as Message Queuing Telemetry Transport (MQTT, www.MQTT.org) or Advanced Message Queuing Protocol (AMQP, www.amqp.org). These system-integrated workbenches easily interface with other hardware and software tools, such as oscilloscopes and condition-monitoring libraries. Access to live and historical data from the application and the process means an analytics workbench can give insights across entire lines and plants. Engineers can therefore compare machine performance and schedule maintenance across global multisite operations, improving efficiency for shorthanded facilities.
Measure and analyze to understand
Vibration-monitoring I/O modules can work in concert with other high-end measurement technologies to provide the most accurate data for a detailed understanding of machine performance. Even general production machines produce many useful metrics for analysis, such as energy consumption, temperature, pressure, material thickness, and weight measurement, in addition to vibration. For example, if a machine begins to draw more power than usual, it could signify poor performance or impending failure, the same way vibration frequently does.
These measurement I/O technologies also rely on the fundamentals of EtherCAT for reading, filtering, and analyzing important production data. Most importantly, they all give crucial information that helps increase machine performance and limit downtime. Engineers can implement new IIoT and Industry 4.0 principles in their manufacturing processes without adding another layer to their control platform, while alleviating the effects of the skilled labor shortage through a simplified engineering environment.
High-end measurement modules have metal housings, EMC protection, and a range of connector types whether they monitor vibration or other key metrics, such as energy consumption, temperature, pressure, material thickness, or weight.
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