2009 ISECS International Colloquium on Computing, Communication, Control, and Management

978-1-4244-4246-1/09/$25.00 ©2009 IEEE CCCM 2009

A study of Steel cord belt magnetic memory testing

System

Tiezhu Qiao,Xuwei

Measuring And Controlling Technology Institute,Taiyuan University Of Technology, China ,Taiyuan, 030024

E-mail:qtz2007@126.com

Abstract Metal Magnetic Memory (MMM) is a new

non-destructive testing (NDT) technique. It is important on early diagnostics of fatigue damages and evaluatuion of life time.In order to check the early injury problems and hidden troubles of the steel-cord belts reliably and sensitively,a new type of system based on Metal Magnetic Memory technology is developed.The designs of sensor ,detection system and software are given.The floating-point DSP chip is used as the microprocessor in the detection system.The new system which is used for steel-cord belts testing has the characteristics of high sensitivity,small lift-off effect and high reliability. Key words : Metal Magnetic Memory ;steel-cord belts;DSP 0. Introduction

Now the steel-cord belt conveyor is the important

transport equipment of the coal mine, metallurgy, ports, large-scale chemical industry, iron and steel enterprises and water conservancy projects.It has the transport characteristics of high speed,long distance,heavy load and so on.However,the steel often has the troubles of rust, broken wires, wear and deformation because of the breakage adhesive tape rope.If the troubles can not be detected and deal with in time,once the steel-cord belt happen the accidents of joint break, serious economic losses and casualties will be caused.At present,the Nondestructive Testing methods,such as ultrasound,ray,magnetic particle, infiltration and eddy current,can test the deficiencies exist,and have high detection rate.But these methods can not solve the early diagnosis problem of fatigue fracture caused by the stress concentration. On the other hand, the traditional methods of NDT have the disadvantages of bulky equipment, labor-intensive,complicated operate,and high quality requirements of operator,and each method has its own limitation[1,2]. Metal Magnetic Memory detection technology can accurately detect the stress concentration zone on the target,so far,it’s the only effective NDT method which can carry out early diagnosis of metal parts[3].

In response to these questions, a new type of intelligent sensor based on Metal Magnetic Memory technology is developed.The sensor can implement the early steel-cord belt fault detection rely on the unique probe design, array sensors optimize design and microprocessor and external circuit design.

1.Sensor design principles

The principle of Metal Magnetic Memory used for

steel-cord belt testing can be expressed as, when the steel-cord belt is running,because of the combined effect of the geomagnetic field and load,it will fatigue and creep.And than the micro-cracks will be formed,the magnetostriction of magnetic domain orientation and irreversible re-orientation will happen in its internal nature.All of these will be Performance in magnetic environment as local magnetic anomaly in stress concentration zone,which called”leakage magnetic field”and maintain after the disappearance of the job load. In this case,magnetic memory non-destructive testing method is used to detect the biggest leakage magnetic field PH changes formed in the concentrated areas of stress and deformation of joints and the decapitated department of the steel-cord belt. The horizontal component )(xH P signal of self-magnetic leakage field has maximum value but normal component of t he signal

)(yH P has a zero value.The irreversible change of magnetic state maintain after the disappearance of the job load.So the stress concentration area of the adhesive tape can be evaluated through measuring the distribution of

)(yH P signals[4].The measuring principle is shown in fig.1.

Fig.1 The measuring principle of MMM

The steel cord belt metal magnetic memory testing method can do rapid diagnosis of the ferromagnetic steel cord joints and the extent of damage of the broken parts.It has the following advantages:

(1)The Stress concentration zone is unknown,it can be measured accurately during the measure.And than the problem of the steel-cord joint and the location of decapitation will be identified accurately.

(2)Compared with the magnetic particle flaw detection,the MMM does not need special equipment to do magnetization on the surface of steel-cord magnetic tape,does not have to carry out post-test

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demagnetization.It can detect use the self magnetization characteristic of the adhesive tape.

(3) Compared with the eddy current testing, the MMM does not need to do special cleaning on the surface of steel-cord belts.The allowable largest lift-off which has protective coating on the surface is 150mm.The lift-off effect is small.But the eddy current testing has more stringent requirements of the stell-cord belts.The lift-off effect is large.

(4)Compared with the ultrasonic testing,the MMM does not need adhesive between the sensor and the surface of measure object.So the problem of adhesive pollution does not exist.

(5)Compared with the traditional ray, ultrasound, and stress testing with strain gauge, the MMM is able to detect the injury endangered status of the steel-cord belts sensitively.And it has unique capacitys of stress-strain state evaluation,equipment intensity and reliability analysis,life prediction and so on. 2.Sensor probe design

After considering the testing principle of metal magnetic memory ,the actual running situation of steel-cord belts and the characteristics of magnetic signal element,select the Hall elements which made of InSb semiconductors as the sense organs of the new sensor probe.Because the steel-cord belt may move vertical only, in order to measure the status of each rope, we need to use array detection.For the sake of improving the scope of the Hall elements' output signals and helping the analysis of detecting signal,we adopt poly magnetic detection to detect magnetism,which is carried out by poly demagnetizer[5].The design principle of the sensor probe is shown in fig.2.

Fig.2 The design principle of the sensor probe

In figure 2,the volume which is detected by a single hall element is an average volume of the space magnetic

field in its induction plane. The measurement of Hall potential HV is:

),,),,( zyxIKdxdyzyxBIKV HS

CHxCHH

H

（φ∫∫ == (1)

In equation(1), HK --Constant, decision by the characteristics of the Hall element.

CI --The current pass into the Hall element.

HS --Induction area of the Hall element. When the current is set as a fixed value, the Hall

potential HV is directly related to ),, zyxH（φ . Add a Poly demagnetizer at each side of the Hall

element induction surface,which has the size of

CCC HWL ×× ,so the magnetic flux ( , , )C x y zφ between two poly demagnetizer can be calculated as follows(neglect the collection effect of the magnetic field at both ends of the Poly demagnetizer.):

dydzzyxBzyxCS

xC ∫∫= ),,(),,(φ (2)

In equation(2), CS --The side area which the two Poly demagnetizers parallel to the xoz plane.

In addition, because of the signal provided by the sensor is a relative volume of the opening width of steel-cord joint and broken.In order to ensure the accuracy of the width of opening measuring,high precision velocimetry sensor is used in the sensor probe design which can ensure that the moving belt operation of 1mm, the speed sensor generates a pulse.The fracture width can be got by calculating the number of received pulses. The measurement method can measure the length of belt accurately and go to the exact location of the joint and broken on the belt.

3.Detection System Design

Because of the different width of most adhesive tape, in order to improve measurement accuracy and reliability, the sensor array design for the three groups, each one shaped by the sensor array, the distance between sensors within the scope of the detection, which format a non-blind scanning detection structure. In order to meet the real-time data collection requirements, improve data acquisition speed, the design select of floating-point DSP chip (TMS320 series), in order to eliminate the Signal frequency aliasing and detect high frequency signals use a low sampling frequency, the non-uniform sampling method is used. The system use the USB interface to connect the site to adapt to different requirements on the number of sensors, sensor signal collected and handled by the DSP, then communicate with the host computer using USB interface. Sensor hardware circuit diagram shown in fig.3.

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Fig.3 Sensor hardware circuit diagram

Detection systems include the following ten modules: (1)Sensor Probe: When the adhesive tape steel cord

through the top of the sensor, the Hall element in the sensor probe sensor of high frequency oscillation signal, the Speed Sensor produce the corresponding pulse.

(2)Filter circuit:Remove interference signal from the measured signals.

(3)Amplifier: Enlarge the usefulness weak input signal to a considerable degree of the amplification and acquisition system in order to obtain the highest possible resolution.

(4)Multi-channel analog switch group: select the several input signal, give the output to the A / D conversion circuit.

(5)Clock circuit:The clock circuit to provide clock to the DSP and CPLD, DSP and CPLD work under the clock.

(6)CPLD (Programmable Logic Device): DSP output clock signal to the CPLD, CPLD delay and divide the frequency of the clock signal, a slower non-uniform clock signal produced and output to A / D conversion chip.

(7)A / D conversion circuits: A / D conversion circuit according to the clock signal convert analog signal to digital signal, using the DB data bus sent non-uniform sampling signal to DSP.

(8)DSP signal processing circuits: DSP calculate the spectrum of the sample, after treatment the result interface to PC via USB for further signal analysis, image reconstruction, display, storage and printing, record leather operation to detect the fault.

(9)USB interface circuit: USB interface connection adapt to the number of the sensor of different site requirements and implement data communication of DSP and the host computer.

(10)Flash memory circuit: Storage detect data, as historical data can be stored and distributed to the PC through USB interface. 4. Software design

When hardware circuit of the sensor is fixed, the main

functions of the sensor are to be realized by software. The software system of the sensor contains several modules such as product of the heterogeneous pulse, data gathering and dealing, gathering data transmission, data analysis and judgment and data display part and so on. The software system can deal the problems as below.

(1)Deal with the gathering lager or small singles of the joint of all sets sealing-tape machine.

(2)Deal with the gathering lager or small singles of the broken ends of all sets sealing-tape machine.

(3)Deal with the distance between joint and broken ends and deal with the names of the joints and broken ends.

(4)Rebuilding, display, storage and print of the test data picture.

The system flow chart shown in fig.4.

Fig.4 Flow diagram for software system

5. Conclusion In the experiment, the new type sensor achieves a

very good application in the steel cord belt detection, and it is well established for its high stability, plug and play, easy installation and accurate positioning.

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