Can Uslu │ Principal, PdMechanics
There are various types and brands of wireless vibration sensors in the Industrial Internet of Things (IIoT) market. The increased number of wireless sensor options with different properties have brought complexity to potential customers. This text aims to present an overview of the wireless vibration sensors and make it easier for the reader to perform market research and ask the right questions to make the right decisions.
Motivations for Wireless Vibration Sensors
The main drivers that make the wireless vibration sensor market grow and find a place in the industrial facilities’ predictive maintenance programs are:
Scalability: It’s easy to scale up the range of the monitored assets with wireless sensors with minimum installation effort. There is no cabling, junction box, or panel requirements as wired systems. In this aspect, wireless sensors are a good choice to implement to balance of plant machinery, which cover the supporting and auxiliary assets in a facility that do not require continuous monitoring as the main critical assets but still need an efficient maintenance program to sustain high availability.
Reduced Workload: Receiving data from wireless sensors in regular intervals eliminates the need to perform manual data collection with handheld devices. This condition reduces the workload of maintenance teams and minimizes staff burden. Instead of data collection efforts, maintenance teams can devote more time to evaluate the collected data, increase asset reliability, and add value to the ongoing maintenance program.
Accessibility: Wireless systems are beneficial to implement in hard-to-reach or potentially dangerous locations. For example, the water industry contains many remote pump stations away from a central facility. It is possible to set up wireless condition monitoring systems in those remote pump stations with minimum investment. Regular data collection from a hazardous environment is common in the sectors such as oil, gas, and steel. Various wireless technologies are available in the market, such as Bluetooth, Wi-fi, or Lorawan, with varying range and data transmission rate capabilities to meet the remote location demands.
Key Aspects of Wireless Vibration Sensors:
-Level of Offered Insight
From a user perspective, it is helpful to classify the wireless sensors with the level of feedback they provide about the machinery condition: the ones with Go/No-go outputs and the ones offering further diagnostic data.
Go/No-go sensors, in general, provide overall vibration velocity and acceleration measurements. The data is then compared with alarm thresholds to evaluate the asset condition. This capability, which is similar to a standard facility SCADA monitoring system with 4-20 mA vibration sensors and PLCs, is valuable for the assets which aren’t monitored yet in a facility or at a remote location, and initiating a predictive maintenance program for those assets will generate maintenance cost savings.
Wireless sensors with diagnostic data provide additional vibration features to the users. The level of diagnostic data depends on the sensor architecture and computational capabilities. Sensors may provide vibration time waveform with the features such as kurtosis, crest factor, and skewness, giving insight into the nature of the vibration forces, such as the impact level and the force asymmetry. With these data, it is possible to have clues on the root cause of the malfunction. In addition to time waveform, a frequency spectrum is also a valuable tool for malfunction diagnosis.
Regarding the memory and battery life considerations, instead of the entire spectrum data, some wireless sensors display the overall vibrations of the specific frequency bands. The user then can define the frequency bands corresponding to the machine’s working frequencies, and for example, if the overall vibration of the frequency band covering vane pass frequency is high at a pump, then the maintenance team can inspect the pump impeller in the next stoppage. This kind of diagnostic feedback helps to minimize the troubleshooting efforts and gain time.
It is essential to remind that there are various applications and assets in the industry where all these sensors with different properties individually fit. Consequently, to achieve a good return on investment, the user should not look for the sensor with the highest capabilities but the one that will meet the demands. If the asset has a few failure modes and its outage will not cause production losses, a simple Go/No-go sensor may be adequate. If we are looking for a solution with more diagnostic outputs to minimize the troubleshooting efforts of critical assets with many components, then time waveform vibration features and spectrum data are helpful. Failure modes of an asset and how the malfunctions manifest themselves in terms of vibration is the question that needs to be answered to decide what level of diagnostic feedback is necessary.
-Maximum Frequency Response (Fmax)
Fmax is the maximum vibration frequency the sensor will capture. Fmax should cover the vibration frequencies of the potential asset malfunctions. For instance, a vibration sensor with an Fmax of 1 kHz can detect faults at shaft rotation speed or its multiples, such as unbalance, misalignment, looseness, damaged impeller, or late-stage bearing fault. As another example, with an Fmax of 10 kHz, it is possible to record high-frequency vibrations and detect malfunctions such as lubrication issues, hydraulic cavitation, early-stage bearing faults, and electrical motor rotor bar failures.
-Data Sampling Interval
Wireless vibration sensor batteries in the market last between three to five years on average by uploading data to the cloud a few times per day. Some brands may have a better or worse performance. In this aspect, wireless sensors may not be adequate for critical assets which require continuous monitoring against rapidly developing malfunctions. In general, the purpose of wireless systems is not to avoid or take action against sudden issues but to follow up the trends and take measures against the gradually developing faults.
-Additional Physical Parameters: Temperature and Rotation Speed
There are also wireless sensors in the market that, in addition to vibration, provide asset surface temperature and rotation speed data. With these additional data, it is possible to analyze the health condition of an asset comprehensively. Regarding the assets with variables speed, rotation speed knowledge is crucial to analyze the frequency spectrum since most of the working frequencies depend on shaft rotation speed. Rotation speed can also provide information about the asset load, which affects the vibration amplitude. Surface temperature is also a valuable parameter for malfunction diagnosis. There may be cases where a surface temperature increase is not accompanied by an increase in vibration, and maintenance decisions are made based on temperature data.