International Journal of Computer Application and Engineering Technology Volume 1-Issue1, January 2012.pp.1-7 www.ijcaet.net DEVELOPMENT OF VIBRATION REMOTE MONITORING SYSTEM BASED ON WIRELESS SENSOR NETWORK Hui WangJinxiang Fan and Kelin Du The Enjoyor Company, Huangzhou city,310030, Zhejiang Province, P.R.China *Biaobiao Zhang Department of Mechanical Engineering, University of Alabama, Tuscaloosa, AL35487, USA *E-mail: bzhang@crimson.ua.edu ABSTRACT: To avoid unexpected equipment failures and obtain high accuracy in diagnoses for the rotating machines, an online vibration monitoring system must be developed. Although many previous techniques for fault detections in rotating machines such as signature analysis using stator current spectra have been well documented, it is until recently that developments in MEMS technology show the increasing trend in integrating vibration analysis for fault diagnoses. This paper describes an innovative way to sample, process, transmit, and analyze vibration measurement data at remote sites and monitor any vibration damages in facilities. As the case study, the system conducts vibration measurements at the remote sensor locations distributed on a wind turbine, then performs vibration signals by using wireless sensor network (WSN) and transfers them to client terminals for processing and analysis through GPRS and internet protocols. KEYWORDS: WSN; GPRS; Vibration monitoring 1. INTRODUCTION Nowadays most manufacture companies are shifting their management strategies from scheduled maintenance to predictive maintenance by observing and predicting machine working conditions in advance [1]. Predictive maintenance is a new approach for facility maintenance. By analyzing data transferred from sensing remote machines through wireless sensor network, people will quickly predict equipment failures so that unexpected disasters can be avoided. Many industrial rotating machines such as motors can be monitored by detecting real-time parameters such as vibration displacements and temperatures from fixed sensors. It should be pointed that traditional monitoring technologies were used in industries for many years, but instruments used for data collection were generally either portable data collectors for manual/walk-around programs or permanently installed online systems that automatically collect and store data. These monitoring systems work but have obvious limits, for instance, expensive costs were spent in installation and maintenance, besides, many facilities to be monitored are not at the same location. To overcome these restrictions, wireless sensor networks can be the good solution. Wireless sensor network [2][3] is a new network that integrates sensors, wireless communication and distributed intelligent processing technology. It can be applied to sample data at remote locations with lower expenses, for
example, ZigBee [4] is a wireless networking technology with characteristics of low power, low cost and short time-delay. These favorable features are applicable in the larger remote monitoring area. In this paper, we develop the ZigBee based WSN for health monitoring in rotating machines. The vibration signals sampled are processed at the remote client terminals through internet protocols. In order to predict levels of severity of rotating machine imbalance, the vibration detection techniques with suitable algorithms are applied to extract detailed information for induction machine fault diagnoses. As illustrated in Fig.1,the wireless technology is capable of operating data sampling, data packaging, and conducts parameter memorizing as well as routing to a data base station; the data collected from the monitoring nodes is then transferred to the remote monitoring center via a GPRS network. The monitoring center analyzes and processes vibration parameters and gives an alarm for emergencies such as vibration damage, in addition, it will provide decision-making in prevention and remediation of machine breakdown. To clarify the remote monitor system, we will introduce ZigBee wireless technology in the following section, then we will describe the system configuration later. 2. ZigBee Wireless Technology ZigBee is a wireless technology operating on the IEEE 802.15.4 physical radio specification in unlicensed bands, including 2.4 GHz, 900 MHz and 868 MHz [5]. ZigBee has found the increasing application in industries for signal monitoring. It is able to meet technical requirements in condition monitoring (e.g., high bandwidth) and has merits in network security and standard implementation. Its power consumption is moderate. Normally in the typical monitoring situation, batteries can last up to one or two years. The ZigBee network consists of three kinds of devices as illustrated in Figure 2. A coordinator, which organizes the network and keeps up routing tables. Routers, which are responsible for communicating with a coordinator, with other routers and the reduced function end devices. Reduced function end devices, which can be connected with routers and the coordinator, but not with one another. 3. Design of the vibration remote monitoring System The WSN based vibration monitoring system shown in Fig.1 consists of two parts: 1) a GPRS network as a long-distance communication section for remote data transmission; 2) a ZigBee network used for vibration response monitor. ZigBee network has the characteristics of adapting network topology easily with features of low power consumption, great network capacity, credible communication and low cost. Therefore, it is suitable for being applied in fields intelligent controlling. To that end, several modules are developed, including terminal controller modules, interface module of GPRS network and system management software. 2
3.1. Hardware design Network nodes and coordinators are key components in the WSN system. Assuming that the coordinator will always be connected with the monitoring center/server through the GPRS network, all messages will be exchanged between the server and the network. When the server sends out a command, the CPU of the network coordinator will read the content of the command and get the details by analyzing it. The main control program within the network coordinator writes the details to the ZigBee module through serial ports. Then the ZigBee module will be responsible for transmitting the messages to the communication network. From Fig. 1, we can see that development of the network coordinator and the ZigBee node is the most important task for the hardware system design. These two components are basically identical. The only difference is that the latter has the function of GPRS communications while the former does not. Therefore, we will describe the design of the ZigBee network coordinator in detail later in this paper. According to the above description, we can find the microcontroller (MCU), the ZigBee module and the GPRS module which are the most important parts of the network coordinator. The hardware construction of our coordinator node adopts MSP430F149 as MCU (from TI), ETRX2ZigBee module, and MC52i GPRS module (from Siemens).We have designed peripheral circuits according to function requirements, and developed a network coordinator by integrating the ZigBee coordinator node and the GPRS module together on a PCB board. Figure 3and Figure 4 show modules of the circuit diagrams designed for the system. The terminal controller of vibration control system is the controlling and actuating devices to implement vibration monitoring and control system. It will be described in following sections. 3.2 Software Design 3.2.1. Client monitoring software The monitoring software at the central monitor station (i.e. monitoring server) shown in Fig.1 adopts C/S architecture based on socket communication mechanisms of TCP/IP protocol. It is written in C# language and built on the.net software with the independent platform and excellent expandability. The client terminals mainly consist of two parts: database management server and system management server. The database management server includes database server and databases. The database management server manages the interaction between various modules and databases, establishes databases and keeps relations with other modules. The system management server interacts with the users. The system management server provides a human-machine interface, through which clients can configure system parameters and monitor real-time data and inquire about historical records. 3.2.2. ZigBee Node software The coordinator node software is responsible for the collection and transmission of data. Sensor nodes have functions such as data sampling, A/D converter, I/O control, timer-triggered and timer-triggered hibernating. Router nodes and coordinator nodes mainly conduct data forwarding and path routing. The router nodes and the coordinator nodes have the capability of collecting sensor data. As such, they can also be treated as sensor nodes. During the interaction between coordinator nodes and the GPRS network, both of them should follow the same datagram protocol in order to enable the host station to analyze the message more easily. Figure 5 shows the flowchart of the node software. Node software is mainly 3
responsible for data transmission between ZigBee network and GPRS network. As for this vibration monitoring system, we apply two-level wireless communication with interface for ZigBee network implemented as the ZigBee Coordinator Node and with interface to GPRS. The ZigBee wireless network would cover the area or around the area that participates in a monitor action. ZigBee Coordinator Node stores information about the network and forwards data to GPRS network as illustrated in Fig.1 above. In two-layer model for monitoring purposes, the ZigBee coordinator node establishes star topology network and communicates with other available ZigBee devices whose implementation type would depend on the transmitted data. When they are necessary to communicate outside of the network, the information would be forwarded to the GPRS interface. 4. Case Study: Avoiding catastrophic due to wind turbine-bearing failure As for previous routine checks, due to hand-held analyzers, the interrupt with plan occurred in a couple of weeks, so it was uncertain whether the wind turbine bearings would function well continuously. With the help of internet-based monitoring technologies, expected benefits are closer to real-time problems detection and better understanding of the turbines vibration behavior [7]. Particularly, by using the wireless monitoring system, 24-hour remote monitoring is offered and real-time data will be vividly transferred to machine operators at the central terminals. As shown in Fig.6, data information of the turbine is sampled through remote sensors and stored into database instantly through network protocols as shown in Fig.1.It should be noted that the turbine online monitoring system consists of two modules: real-time monitoring and off-line analysis as shown in Fig.7. Functions of real-time analysis module include signal processing, feature extraction, model and pattern recognition, etc. Off-line module can conduct signal trend analysis and fault feature retraction. The system analyzes signals in time-domain and frequency-domain methods continually. In case some abnormal are found, the system will shift to fault diagnosis module automatically. Figure 8 shows an example of bearing faults and cepstrum analysis. A Cepstrum analysis is useful for detecting harmonics exhibited by a faulty roller bearing in the wind turbine. A roller element bearing is composed of an outer ring, an inner ring, and several roller element balls. When a failure develops in the outer or inner ring, the measured vibration signal will exhibit larger frequency energy around the fault frequency of the inner or outer race [8]. 5. Conclusion Rapid progress in the field of MEMS will enable the development of remote wireless sensor network for sampling, digitizing and transmitting real-time signals from remote locations. The ZigBee network as a typical wireless sensor network employs a number of sensors to communicate with client monitoring terminals through GPRS and internet network in the hope of tackling with working machine vibration problems at any time. In this paper, the vibration remote monitoring system consists of three parts: data monitoring nodes, GPRS/Internet and remote monitoring terminals. It presents us with features such as large monitoring ranges, flexible configuration, low power consumption, small damage to the environment and low cost. As the case study, the system is applied to perform online monitoring work on vibration amplitudes of a wind turbine. Sensors accessing to sample different vibration amplitudes can help the clients at the terminals to detect any unexpected failures occurring in the wind turbine timely, therefore this system thus promises broad applications. 4
Fig.1.WSN-based vibration remote monitoring system Fig.2 A ZigBee based networks incorporating coordinators, routers and end devices in a mesh topology Fig.3. Schematic of ZigBee circuit Fig.4. Schematic of GPRS circuit 5
Fig.5. Flowchart of node software Fig.6.Wind turbine vibration monitoring site 1, 2Vibration (acceleration, bearing, radial); 3, 6 Vibration (acceleration, bear box, radial); 4, 5 Vibration (acceleration, generator, radial); 7 Vibration (acceleration, hood, radial) Fig.7. The software system flowchart. 6
Fig.8. Power spectra and Cepstrums monitoring of a bearing [8] References [1] ELECTRIC POWER RESEARCH INSTITUTE, Electric Motor PredictiveMaintenance Programme, TR- 108773-V2, Palo Alto, CA, USA (1999). [2] Ivan Stojmenovic, Geocasting with Guaranteed Delivery in Sensor Networks,IEEE Wireless Communications, December 2004,pp. 29-37. [3] Kay Romer, Friedemann Mattern,The Design Space of Wireless Sensor Networks,IEEE Wireless Communications, December 2004,pp. 54-61. [4] IEEE 802.15.4. http://www.ieee802.org/15/pub/tg4.html [5] Adrian Perrig, John Stankovic and David Wagner, Security in Wireless Sensor Networks, Communications of the ACM, Vol. 47,No.5, pp. 53-57, June 24. [6] Ran Chen,The Smart Three-Phase Electric Meter Based on ENC28J60 and MSP430F149,Advanced materials research,211-212,pp.1230-1234,2011 [7] J.B. Ekanayake, L. Holdsworth, W. XueGuang, N. Jenkins,Dynamic modelling of doubly fed induction generator windturbines, Trans. on Power Systems, Vol. 18, No. 2, May2003, pp.803-809. [8] National Instruments, Vibration Analysis and Signal Processing inlabview,feb 23(2011). 7