NORPIE 2004 Trondheim, 14 June A Low-Cost Measurement and Data Collection System for Electric Motor Condition Monitoring Anna-Lena Rautiainen Risto Tiainen Jero Ahola Tuomo Lindh

Introduction Condition monitoring includes measurements, analyses and decision-making based on the results of the analyses The analyses can be made at the same place as the measurements or at the same place as the decision-making –The former case is the embedded analysis, the latter the higher-level analysis

In this presentation, a system with remote analysis is concerned

Why Remote Analysis? Sensor equipment can be made simpler and thus more inexpensive –Inexpensive systems allow the extension of the on-line condition monitoring to targets where it otherwise would not be economically feasible –Embedded analysis requires more data processing capacity and memory at the sensor level –Desktop PCs offer cheap computing capacity

Why Remote Analysis? The analyses of the data of several sensors can be made at a single computer –Updating the analysis software and introducing new analyses is easy The system is generally more flexible and more easily customisable –All the measured data is available at the place of the decision-making

Why Embedded Analysis? Only the results of the analysis need to be transferred to the management level => lower transmission capacity required

Overview of the Constructed System Vibration- and temperature-measuring sensors were developed Sensor units must be made as simple as possible in order to keep the system cost low –Simple 8-bit microcontroller, no external memory … The capacity of the sensors’ RAM is not sufficient to hold a single vibration measurement Therefore, a unit that receives the measurement data real- time and provides a temporary storage must be present

Multiple sensor units must be able to be connected to one collector unit Alternatives: –A point-to-point type connection between the collector unit and each of the sensor unit –A bus connecting the collector unit and the sensor units

Multi-Channel vs. Sensor Bus

Alternative 1: Multi-Channel Pros –Simple communications protocol –Better reliability Cons –Fixed number of channels –More electronics (and connectors) needed on the collector unit board

Alternative 2: Sensor Bus Pros –Flexibility: the chain of sensors can be easily extended –Less electronics required on the collector unit board Cons –Worse reliability –Tends to make the sensor units slightly bigger than in the case of the multi-channel realisation (two cables required, bus entry and exit)

The Developed System The bus-based approach was selected –flexibility

Communications from the Collector Unit Upward The data must be transferable from the collector unit to a higher level in the industrial information infrastructure This must be done without new cabling Possible solutions: using existing infrastructure (field buses), wireless communications, power- line communications … In the developed system, the Modbus protocol atop a twisted-pair RS485 connection was used

The Principle of the Structure of the System

The Developed System – The Sensors The sensors measure vibration and temperature Built around the Microchip PIC16F876 microcontroller Vibration measurement –The Analog Devices ADXL105 micromachined silicon accelerometer (analogue output) –Digitised with the precision of 12 bits, at a sampling frequency of 20 kHz –One measurement: samples Temperature measurement –Using the temperature sensor in the ADXL105 –Digitised using 10 bits with the internal ADC of the PIC

The Developed System – The Collector Microchip PIC18F8720 microcontroller 64k x 16 SRAM Connected to the sensors via a RS485 bus (625 kbps) Supplies the power to the sensors

Pilot Installation UPM Kymmene Kuusanniemi pulp mill 630 kW, 1500 RPM machine driving a mass pump –Two sensors: one fastened to a bearing of the motor, the other to a bearing of the pump The collector connected to a PC via Modbus, the PC to the University via GSM modem link