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Remote control of electromagnetic load emulator

for electric motorsBozic Milos; Rosic Marko; Bjekic Miroslav

Faculty of Technical Sciences, University in Kragujevac, Serbia

Abstract This paper presents equipment and application

for remote control of electromagnetic load emulator.

Emulator is dedicated for testing of electrical motors in

laboratory environment. It can emulate different kinds of

loads which can be found in industrial environment like

pumps, funs, conveyors, elevators etc. The working

principle of electromagnetic emulator is based on

electromagnetic induction. Emulator control is realized with

CompactRIO controller that has a web server so it can be

accessed remotely. Programming is done via LabVIEW

software.

I ndex Terms CompactRIO, emulator, motor, labview,

remote.

I. INTRODUCTION

For making a real work regime of one electrical motorin laboratory environment, it is necessary to load the shaftwith certain torque. For this purpose, the different types ofloads are in use (mechanical, hydraulic, electrical, etc.).Electric loads are usually implemented as a complexelectromechanical group which is the optimal solution forthe precisely controlled torque. One of the most importantcharacteristics of electrical motors is efficiencycharacteristic, which can be obtained by measuring of

speed and shaft torque precisely [1].Standard laboratory tests that are performed in the

laboratories of the electrical machines are no load andshort circuit tests according to standard IEC 60034 - 2.These tests represent extreme points of work regime of anelectric motor. The most interesting is working regime

between these two points, which can be obtained byapplying the load to the shaft, in this case with loademulator. In this conception load torque is specifiedindirectly with a current through the electromagnetwindings.

Laboratory classes are very important for futureengineers. Most of the laboratory classes are performed ingroups. This conception brings that some students are

actively involved in exercise while the rest of the group isonly present in the laboratory. Solution for this problemmay be if every student individually does laboratory

practice. Due to lack of time and equipment most often itis not the practice. The introduction of a remote laboratoryexercises brings that students are actively involved incarrying out experiments. Also, this concept would allowinstitutions that do not have the necessary equipment toremotely perform the exercises. It can be faculties orsecondary vocational schools [2] [3].

II. MAIN PARTS OF THE EMULATOR

The main parts of the system are presented in figure(Fig.1).

Fig. 1. The main parts of the system

1. CompactRIO 9074 integrated system combines a real-time processor and a reconfigurable field-programmablegate array (FPGA) within the same chassis for embeddedmachine control and monitoring applications. It integratesa 400 MHz industrial real-time processor with a 2M gateFPGA and has eight slots for NI C Series I/O modules. Ithas two 10/100 Mb/s Ethernet ports that can be used toconduct programmatic communication over the networkand built-in Web (HTTP) and file (FTP) servers as well asto add expansion and distributed I/O to the system [4].Modules used in this system are:

- NI 9402 is a 4-channel, 55 ns bidirectional digitalmodule. Digital lines can be configured as input andoutput.

- NI 9227 is current input module designed to measure 5A RMS, and has 50 kS/s per channel simultaneoussampling. Function of this module in system is to measurecurrent through electromagnets.

- NI 9403 is a 32-channel, 7s bidirectional digitalinput/output module. Purpose of this module in system is

to measure speed of shaft rotation.

2. Control interface contains DC power supply forelectromagnets, 0 - 350VDC, 3A; PWM amplifier andSensor for measuring speed of motor shaft.

DC Voltage

PWM amplifier

TTL output

NI 9402

Current module

NI 9227

Shaft

Digital Hall

Sensor

Digital input

NI 9403

Magnet

cRIO 9047

Electromagnets

Fig. 2. Block diagram of electrical connections

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3. Electromagnetic emulator is calibrated retarder. Theelectric retarder uses electromagnetic induction to providea load torque. There are no contact surfaces between therotor and stator, and air gap is 0.7 mm. When load torqueis required, the electrical windings in the stator receive

power, producing a magnetic field through which the rotormoves. This induces eddy currents in the rotor, which

produces an opposing magnetic field to the stator. Theopposing magnetic fields slows the rotor, and hence theshaft of attached electrical motor. The operation of thesystem is extremely quiet in contrast to mechanical

braking. Electromagnet winding has 700 turns of 1 mm2

copper wires. Electromagnets can be connected in seriesor parallel, or combined depending on the desiredinduction. Projected maximal torque is about 100 Nm.

Desired torque is achieved by measuring speed of shaftrotation, and with PID controlled current throughwindings. The required current for actual speed iscalculated from relatively complex math equations whichare obtained from calibration process. Desired torque isachived with current feedback, and there is no need forusing an expensive torque sensor.

Fig. 3. 3D model parts of electromagnetic emulator(1cantilever, 2electromagnets, 3rotor disc)

4.IP camerais standard camera. It is connected to secondport of cRIO, and allows web casting during experiment.

III. EMULATOR APPLICATION

Emulator application is realised in LabVIEW. Timecrtical current loop is written on FPGA, measuring speedand equations calculations are implemented on Real timemodule. Fig. 4 shows applications front panel with its

parts during the experiment.

Fig. 4. Load characteristics tab with parts of application:1,2,3,4Load characteristic type and its parameters; 5,6,7 speed diagram; 8speed - torque characteristic; 9 - current diagram; 10 torque diagram

IV. CONCLUSION AND FURTHER STEPS

In this paper remote control of electromagneticemulator for electric motors is presented. Students in thisexperiment can adopt practical knowledge about PIDtuning and electric motor load characteristic. Afterfinished experiment most important parameters can besaved in a form of laboratory document report.

Some further steps will be adding sensors for measuringtemperature in electromagnets and also in motor duringexperiment. Adding microphone besides video feedbackusers will have and audio feedback. With audio feedbackstudents can hear sound of motor with no load and loadedmotor. Besides measuring the current of the emulator,current and voltage of the motor will be measured to.

ACKNOWLEDGMENTThis paper is a result of activities within the project

543667-TEMPUS-1-2013-1-RS-TEMPUS-JPHES

Building Network of Remote Labs for strengtheninguniversity-secondary vocational schools collaboration

supported by The Education, Audiovisual and CultureExecutive Agency (EACEA).

REFERENCES

[1] M. Boi, M. Rosi, B. Koprivica, M. Bjeki, S. Anti.,Efficiency classes of three-phase, cage-induction motors (IE-code) software, INDEL2012, IX Symposium IndustrialElectronics, INDEL 2012, pp 87-91, November 1-3, Banja Luka,Bosnia i Hercegovina, 2012

[2] L. D Feisel,. and G. D. Peterson, Learning ObjectivesforEngineering Education Laboratories, 32nd ASEE IEEEFrontiers in Education Conference, Boston MA. 2002.

[3] L. D. Feisel, and A. J. Rosa, The Role of the Laboratory inUndergraduate Engineering Education, Journal of EngineeringEducation, 94(1) pp. 121-130, 2005

[4]

National Instruments. CompactRIO cRIO-9074 [PDF Manual]Available at:http://www.ni.com/pdf/manuals/374639e.pdf.

http://www.ni.com/pdf/manuals/374639e.pdfhttp://www.ni.com/pdf/manuals/374639e.pdfhttp://www.ni.com/pdf/manuals/374639e.pdfhttp://www.ni.com/pdf/manuals/374639e.pdf