# Condition-Based Monitoring and Maintenance: State of the Art Review
## 1 Introduction  
Condition monitoring is the process of observing a set of parameters and/or variables that indicate that the state of the system under investigation. It plays a significant role in the maintenance, management, and sustainable operations of various sectors, such as manufacturing industries [1, 2, 3, 4], transportation [5, 6], energy [7, 8, 9], natural resources [10, 11, 12, 13], both natural and human-made disasters [14, 15], and healthcare [16, 17]. In most cases, sensors and/or micro-controllers are widely used to perform condition monitoring [18, 19]. In particular, in this paper, our focus is to provide a comprehensive review on various condition monitoring approaches and their applications in the maintenance in manufacturing industries.  
In terms of manufacturing industries, condition monitoring generally recommends a set of maintenance requirements in the event of failure or malfunctioning of the vital devices or equipment of the system concerned; thus, the entire process can also be termed as condition-based maintenance (CBM) [20, 21, 22]. It can be viewed as (i) a mechanism of preventive maintenance, thus effective in planning maintenance scheduling; (ii) a comprehensive tool for assessing both of the diagnostic and prognostic conditions; (iii) an assistive method in configuring system requirements and also enhancing the capability of conducting regular evaluation and/or maintenance operations; and (iv) a technique to optimize the operational availability of devices, equipment, and modules of various systems [23, 24]. In general, it provides several advantages, such as (i) reducing downtime and maintenance expense by eliminating unnecessary maintenance; (ii) providing an early failure detection to increase asset availability, avoiding unnecessary downtime; (iii) supporting continuous improvement ensuring accurate and consistent response to developing conditions; (iv) providing better decision making for operations, engineering, and maintenance staff; (v) providing integration of control, safety, and maintenance environments; (vi) facilitating the opening of an operator's time to manage assets; (vii) enabling an organization to turn data into actionable and valuable information; (viii) evaluating the equipment activitiesand statistics, not normally maintained in repair logs; (ix) providing a repository to capture the conditions, rules, and other tacit knowledge; (x) allowing the organization to retain intellectual property as the workforce changes; (xi) supporting safety and security to avoid major catastrophic disasters; and (xii) improving morale of the workforces and users [25; 26; 27]. Despite the above-mentioned advantages, it has some drawbacks, such as (i) the initial installation costs being even higher than the system under monitoring, and (ii) uncertainty associated with the failure of the condition monitoring devices [27; 28; 29].  
The concept of CBM was developed in the 1940s; however, its significant utilization has been observed since the late 1990s [30]. It is also related to the technological advancements (in particular to electronics and communication) in the condition monitoring devices and propagation of the information to the system analyst [31; 32]. It has become increasingly more important along with the progress in the field of automation engineering [33]. In order to synthesize the progress of CBM, we provide a literature review in Section 2, CBM-related research activities in the post-secondary institutes in Section 3, and finally concluding remarks and future research in Section 4.