NORPIE 2004Trondheim, 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

Field Level

ManagementLevel

Process

Sensor Sensor

Data analyses andsupervision of results

Measurements anddata collection

Sensor

• 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

Point-to-pointconnections

Collectorunit

Sensorunit

Sensorunit

Sensorunit Sensor bus

Collectorunit

Sensorunit

Sensorunit

Sensorunit

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

SLAVE

SLAVE

SLAVE

MASTER

SLAVE

MASTER

MASTER(PC, PLC etc.)

Collector unit

Sensor unit

SLAVE

SLAVE

Higher level Communication bus(Profibus, TCP-IP etc.)

Field bus

Sensor bus

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: 32 768 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

FTP/WWW-server

Lappeenranta Univ. of Technology

Remote diagnostics

Control room

FTP-server

Collectorunit

M

A,T

Mass pump

RS-485

Modbus

RS-485

Bleaching Line 4

UPM-Kymmene Kuusanniemi Pulp Mill

GSM

Internet

A,TSensors

P