# Condition-Based Monitoring and Maintenance: State of the Art Review
## 2 Literature Review
### Web and Wireless in CBM  
Web-enabled remote monitoring is also used for condition-based maintenance [131]. It can collect data through sensors remotely and transfer the critical information for further processing and analysis. XML and web technology could be used to integrate remote equipment, devices, installations, etc., for data transfer and decision making. Ali et al. [132] introduced the emerging field of e-maintenance and its critical elements. Furthermore, performance assessment and prediction tools are introduced for continuous assessment and prediction of a particular product's performance, ultimately enabling proactive maintenance to prevent a machine from breakdowns. Kwon et al. [133] discussed the current trends in industry, which include an integration of information and knowledge-based network with a manufacturing system, which coined a new term, e-manufacturing, and focused on the accessibility to a remotely located system and having the means of responding to a changing environment. Within the framework of the web-enabled robotic system, it focuses on the remote maintenance schemes with an emphasis on condition-based maintenance strategies with mathematical modelling of system availability in the subsystems of the robot. Marquez et al. [134] developed algorithms to detect gradual failure in railway turnout with an RCM2 approach to the management of switch and crossing maintenance and demonstrated the approach using data from tests on a commonly found point mechanism by adopting a Kalman filter for pre-processing the data collected during tests. In the same year, Pedregal et al. [135] used RCM2 predictive maintenance of railway systems based on unobserved component models. Tiwari et al. [136] developed a wireless sensor network for machinery condition-based maintenance (CBM) in small machinery spaces using commercially available products. A LabVIEW graphical user interface is used for signal processing, including FFT, various moments, and kurtosis using a wireless CBM sensor network on a heating and air conditioning plant. Tiwari et al. [137] presented a wireless sensor network for machinery CBM using commercially available products, including a hardware platform, networking architecture, and medium access communication protocol on a Heating and Air Conditioning plant. Djurdjanovic et al. [138] developed an infotronics based prognostic approach for product performance degradation assessment and prediction. They called it \"Watchdog Agent\", and it is used for multi-sensor assessment and prediction of machine or process performance and can be utilized to realize predictive CBM, CPLM, and identification of components with significant remaining useful life. All the related work on web and remote systems is limited with a firewall of information since different applications need different types of protocols for communication. Since sensors have the limited of transferring data, web-sensors might be helpful to transfer data from source location to remote decision maker location. These kinds of web sensors might have a large impact in monitoring, especially in environment-related condition monitoring.