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Trihology International Vol. 30, No. 4, pp. 275-278. 1997 0 1997 Elsevier Science Ltd

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on-line condition monitoring tern linked by fibre-optic ital network

Liu Ym*+, Wen ShiZhu* and Xie YouBai*

This oaper introduces the basis structure and major function of an on-line condition monitoring system linked by a fibre-optic digital network. Fibre-optic digital networks have obvious advantages to larger enterprises with various locations for condition monitoring data transmission, which not only is an information highway between the main station (diagnosis enter) and substation (monitoring locations), but also combines the montoring functions into one system. This is a two-level condition monitoring system. The first level monitoring is realized by a sub-station and the second level monitoring is realized by the main station. The system has strong hardware functions and software functions, which became a new model of real-time condition monitoring and was used in many oil refineries. 0 1997 Elsevier Science Ltd. All rights reserved

Keywords: condition monitoring, fibre-optic transmission, failure diagnosis, network

Introduction

The technology of mechanical condition monitoring and failure diagnosis has tended to the model of on- line monitoring and centralized data management. This kind of model can utilize advanced data communi- cation technology, building an information highway between the diagnosis centre and the monitoring locanons. In this way, the data from monitoring locations are transmitted to the diagnosis centre timely, and then spectrum analysis, database manage- ment and intellect diagnosis should be made by com- puter at the diagnosis centre. This kind of monitoring model is necessary and effective for larger enterprises whose locations are scattered.

The ,diagnosis centre (which is called the main station in tte following), monitoring locations (which is

*Naticmal Tribology Laboratory of TsingHua University, Beijing 100084, P.R. China fCorrj.spondirzg author: Liu Yan, Theory of Lubrication and Bearirzg Instituie, Xi’m Jiaotong University, Xi’an, Shamxi 710049. P.R. China E-maid: tlbi@.xjtu.deu.cn $Theory of Lubrication and Bearing Imtitute, Xi’an Jinotong Litliver- sity, F7’m, Shnar~si 710049. P.R. China Recril.ed 19 July 199.5; revised 14 Februar?/ 1996: accepted 30 Judy i996

called sub-station in the following) and the digital communication system are disposed in its entirety, and as a system, the three parts above are indivisible. The main station and sub-station are set in the area of factories. The computer of the main station carries out database management, intellect diagnosis etc, the characteristic of which is that the condition infor- mation is analysed, judged and managed through com- bining software with the operator. The computers of the sub-station and other devices carry out real-time data collecting, threshold limit value monitoring, abnormal condition warning, and the focal point of which is that the condition information is obtained speedly and exactly. As an information channel, the main station and sub-station are connected by the digital communication system.

There are some kinds of digital communication system which can be used in the condition monitoring system. However a new kind of fibre-optic digital communi- cation system has been used in the condition monitor- ing system. The major advantages of this communi- cation system are strong anti-interference and the communication functions have been incorporated into the condition monitoring system when it is used in factory environments.

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On-iine condition monitoring: Liu Yan et a/.

Structure of the condition monitoring system

The condition monitoring system with decentralized monitoring and centralized management includes three parts. The main station, the sub-station and the fibre- optic digital communication system, the structure of which is shown in Fig. 1.

In fact, this is a two-level condition monitoring system. The first level monitoring is realized by the sub- station. The condition parameters, such as vibration, temperature, pressure, wear and other technological process parameters of the machines monitored (the blower, the steam turbine etc.), should be monitored timely through the sub-station’. One sub-station can monitor more than three machines. The second level monitoring is realized by the main station and one main station can manage more than seven sub-stations. The sub-station is composed of the sensors, the signal pre-processor, a 486 computer, and an on-line ferro- graph. The sensors are used for detecting changes of displacement, acceleration, temperature and pressure etc. in machines. The signal pre-processor is a device with multiple features, multi-channels for signal pro- cessing, which regulate the signal detected by sensors into a regulor signal suited to A/D transformation. In the signal pre-processor, the AC composition and the DC composition in the vibration signal can be pro-

cessed separately, which are due to the AC showing the vibration of the shaft and the DC showing the displacement of the shaft in the rotating machine. The 486 computer in the sub-station not only can show the signal waveform and analyse the signal spectrum, but also can record the failure signal swiftly with a black- box and forewarn the failure’. The on-line ferrograph is a device which can monitor the amount and size of wear debris in lubrication oil flowing continuously. It is used for monitoring the key tribo-pairs of machines such as gear box, cylinder, piston ring etc. As a part of condition monitoring system, the device is connected to the computer of the sub-station through an RS232 serial interface I/O port, the data of which are trans- mitted to the main station by a fibre-optic digital communication system also. The computer of the main station carries out the task of monitoring the sub- station. The multiple functions software supports the main station, which includes intellect diagnosis, precise diagnosis, on-line dynamics analysis, stability analysis, start-stop analysis, trend analysis, holospectrum analy- sis and database management etc. The main station possesses the function of starting and resetting the sub- station through the data communication system also3. The fibre-optic digital network links the main station and sub-station. Its main task is data transmittion at a high rate between the main station and sub-station; however, it has functions of assisting monitoring.

r-l CRT

Main station

Communication system

Fibre-optic cable

1

I I I I I L’J

Fibre+optic Fibre-optic Communication Communication

system system

I I

Steam Hydrogen turbine compressor

Smoke Blower Steam turbine turbine box

Fig. I The structure of the condition monitoring system

276 Tribology International Volume 30 Number 4 1997

Sub-station change board

Communication interface

hoard

Receiver Transmitter

Fig. f The hardware structure between two points

Fibre-optic digital network

The history of long-distance exchange with fibre-optic transmission is about 20 years. However, it is rare to use fibre-optic transmission in condition monitoring systems. Because there is strong electro-magnetic inter- ference in locations (power stations, refineries etc.) where the condition monitoring systems are used, it has obvious advantages to use fibre-optic rather than cable for interference-free operation.

The fibre-optic digital network is a special purpose communication system. The connective mode of the fibre--optic digital network can be seen in Fig. 1.

The hardware structure between two points connected by fnre-optic cable is shown in Fig. 2. The transmitter is a GFM234 LED, and the receiver is a GJF 357 PIN-FET. The wavelength is 1.3 pm and the light power is -22 dBm. This light transmission-receiver pair can .-ealize communication over about 5 km, which is suitable for most locations. The communication inter-

On-line condition monitoring: Liu Yan et al.

face board is a expanding system with an 8098 or 80C196KC microprocessor-controller, which is inserted in the bus slots of the 486 computer. There are two two-way I/O ports (8 bit) which connect the data bus between the 8098 or 80C196KC and the 486 computer. One is used as an order port, another is used as a data port; there is 54 k RAM in the communication interface board as a data buffer. If the amount of data is more than 54 K for one communication, the data are transmitted in batches. Transmitting and receiving are realized by the serial I/O port of the 8098 or 80C196KC. The rate of serial asynchronous communi- cation is 187.5 kbitfs to the 8098 or 1 Mbit/s to the 80C196KC, which are 20-200 times faster than ordi- nary fibre-optic communication systems with the RS232 serial I/O port of the computer.

The sub-station change board is a controller for chang- ing channels of seven sub-stations. The 74LS138 and 74LS125 are used in the electric channel selection and the channels which are not selected are set in high impedance. In fact, the communication between the main station and sub-station consists of two processes. One is serial communications between the main station and sub-station through two communication boards inserted in the computers and the other is parallel communication betweeen computer and communication interface board through the bus interface. However, the information form and communication agreement are the same in both serial communication and parallel communication in the system. The information form includes order number, data length, checking code etc.

Because the communication board in the main station is a microcomputer system, it can undertake monitoring

r

t+

4 Read order port,

if have communication order?

If timer exceeds 5 min?

Receiving data from

Transmitting order and data to sub-station

and if exceeds

L Fig. 3 Flowchart of the program module qf communicntion board

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On-line condition monitoring: Liu Yan et al.

Table I Type and number of sigrials of the two workshops

Signals Workshop Rotation Acceleration Vibration or Bearing Slow change speed displacement temperature signals

Hydrocracking workshop 1 4 IO 8 16 Catalytic cracking 1 4 20 8 24 workshop

of the sub-station toLlr automatically when the 486 computer of the main station leaves the environment of monitoring. If an abnormal condition flag is found: the communication interface board will give an audible warning. A flowchart of the program module of com- munication board is shown in Fig. 3.

Application and conclusions

The on-line condition monitoring system linked by fibre-optic digital network has been used in LanZhou Oil Refinery (China), TianJin Oil Refinery (China), JiLin Oil Refinery (China) and MaoMing Oil Refinery (China) etc., for a long time. An example application of the MaoMing Oil Refinery is given in here. In fact, the structure of the condition monitoring system of MaoMing oil Refinery has been shown in Fig. 1. There are two rotating machine sets which should be moni- tored in at different locations. One is a hydrogen compressor set, which run in the hydrocracking work- shop and the other is the turbine and blower set which runs in the catalytic cracking workshop. In the diagnosis centre, there is a main station.

The distance between main station and the hydrocrack- ing workshop is 2 km, and the catalytic cracking work- shop is 2.5 km away. So the main station and two sub-stations are linked by a fibre-optic digital com- munication system. The kinds and number of signals are listed in Table 1.

In each sub-station, the computer operates circular signals acquisition over a period of l-2 s. Of course, over the period, some simple diagnoses are made. In the main station, the computer displays the vibration waveform. In Fig. 4, an example is given which is the waveform of two vibration channels. The waveform of the vibration signal in each channel consists of 1024 sample points which are transmitted from the sub- station by the fibre-optic digital communication system. The on-line ferrograph monitors the lubricant in the gear box whose data are transmitted to the main station also by the fibre-optic cable.

The results with the above user show that the system has strong anti-interference features and high stability. It can meet the need of condition monitoring of rotating

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Fig. 4 The waveform of vibratiorl channel

machines in many locations in adverse circumstances, and open up new applications for fibre-optic communi- cation also.

Acknowledgements

The authors express their graditude to LanZhou Oil Refinery, TianJin Oil Refinery, JiLin Oil Refinery and MaoMing Oil Refinery for their help and cooperation, and to the National Natural Science Foundation of China and Doctoral Degree Education Foundation of China for their support to Xi’an Jiaotong University, since most of the research for this system was carried out in the Theory of Lubrication and Bearing Institute of Xi’an Jiaotong University.

References

1. Mitchell J.S. Introduction to Machinery Analysis and ,Monitor- ing, Petmvell Tdsu. OK, 1993

2. Liu Xiong Rotor Monitoring and Diagnosis Analysis, Xi’an Jinotong University Publishing, Xi’nn, China I991 (in Chinese)

3. Reiter R. A Theory of Diagnosis from First Principles, Artzz liztel. 1957

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