Automatic speed and torque monitoring in induction motors using ZigBee and SMS

Arun Nadh

M.E (Communication Systems), Electronics & Communication Department, Dhanalakshmi Srinivasan Engg. College,

Perambalur, Tamil Nadu, India, Email Id: arunnadh@yahoo.co.in

Lakshmi Praba N. Research Scholar, Anna University, Chennai, Electronics & Communication Department, Dhanalakshmi Srinivasan Engg. College,

Perambalur, Tamil Nadu, India, Email Id: laksh_abi@rediffmail.com

Abstract- This project is for monitoring the speed and torque in induction motors in real time by employing ZigBee based wireless sensor network. An embedded system is used for acquiring electrical signals from the motors in a noninvasive manner. The processing for speed and torque estimation is done locally. Embedded system is used to control the speed of the motor. The values calculated by the embedded system are transmitted to a monitoring unit through ZigBee based wireless sensor network. The real time monitoring of various motors can be done at the base unit. Speed of deployment, maintenance, low cost, security, reliability and throughput are the main advantages of using ZigBee. From simulation, plot for output voltage, output current, speed and torque can be obtained by applying different load values.

Keywords-Induction motors, embedded systems, torque measurement, speed estimation, ZigBee based wireless sensor networks (WSNs).

I.INTRODUCTION

This system aims at monitoring the speed and torque in induction motors. An embedded system is used for acquiring electrical signals from the motors in a noninvasive manner. It performs local processing for speed and torque estimation. The values calculated by the embedded system are transmitted to a monitoring unit through a ZigBee based wireless sensor network. Local processing capability is essential for this type of application.

Motor systems use nearly 70% [1] of the total electric energy consumed by industry in the U.S. Among industrial motor systems, three-phase induction motors are dominant because of their simple design, rugged performance, and easy maintenance. AC induction motors, [2] which contain a cage, are very popular in variable-speed drives. They are simple, rugged, inexpensive and available at all power ratings. Progress in the field of power electronics and microelectronics enables the application of induction motors for high-performance drives, where traditionally only DC motors were applied. AC induction [3], [4] drives offer the same control capabilities as high performance four-

quadrant DC drives. This drive application allows vector control of the AC induction motor.

Torque is one of the main parameters for production machines. Torque measurements [8] can identify equipment failures in oil and gas, mining, sugar and alcohol industries. There are mainly two types of torque estimation.

1) Direct torque measurement on the shaft

2) Estimated torque measurement from motor electrical signals

Measuring directly the rotor speed � can be impractical in some cases. Several methods of sensorless rotor speed estimation have been proposed. Embedded system is used for determining speed and torque in industrial electric motors by employing WSNs [5], [13] technology. For a set of electric motors, current and voltage measures are gathered for later processing into an embedded system. Speed and Torque results of the induction motor [15] are then sent to a base unit for real-time monitoring. Wireless sensor networks [14] presents a number of advantages compared to wired networks. In addition to that, wireless sensor networks (WSNs) [9], [11], [12] provide self-organization and local processing capability. Therefore, these appear as a flexible and inexpensive solution for building industrial monitoring and control systems. ZigBee based wireless sensor network is used here. ZigBee allows the formation of a large network of sensors, in various industrial segments. . This standard has been employed also in the mechatronics field. In comparison with other standards such as IEEE 802.11 (Wi-Fi) [16], [18] and IEEE 802.15.1 (Bluetooth), the ZigBee standard has advantages related to energy consumption, scalability, reduced time for node inclusion, and low cost.

II. RELATED WORK

An induction or asynchronous motor [6] is an inherently self-starting AC motor in which energy is transferred by electromagnetic induction from a primary winding to a secondary winding. The two windings being separated by an air gap and such

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Fig.1. Transmitter side

transfer usually from the stator to either a wound rotor or a short-circuited squirrel cage rotor. It is the existing system. Induction motor [19] is used here. Induction motor used is three phase induction motor. It is advanced than single phase induction motor. Three phase induction motor is self-starting. It is an asynchronous motor. Speed can be controlled by varying the voltage.

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, solid-state diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches.

A 3 phase inverter is an electrical power converter that changes direct current (DC) to alternating current (AC). The inverter performs the opposite function of a rectifier. The electrical inverter is a high-power electronic oscillator. Three-phase inverters are used for variable-frequency drive applications and for high power applications such as HVDC power transmission. A basic three-phase inverter consists of three single-phase inverter switches each connected to one of the three load terminals. For the most basic control scheme, the operation of the three switches is coordinated so that one switch operates at each 60 degree point of the fundamental output waveform. This creates a line-to-line output waveform that has six steps. The six-step waveform has a zero-voltage step between the positive and negative sections of the

square-wave such that the harmonics that are multiples of three are eliminated as described above.

Fig. 2. Three Phase inverter

The embedded system used here consists of peripheral interface controller, PIC16F877A. Microchip the second largest 8-bit microcontroller supplier in the world is the manufacturer of the PIC microcontroller and a number of other embedded control solutions. PIC16F877A is an open loop peripheral controller. Program to find out the speed and torque are written in this microcontroller. It is an 8 bit controller. It is having 40 pins. The operating frequency is 20MHz. Flash memory is 14.3 kb. Data SRAM is 386 bytes. The PIC16F877A CMOS FLASH-based 8-bit microcontroller is upward compatible with the PIC16C5x, PIC12Cxxx and PIC16C7x devices. It features 200 ns instruction execution, 256 bytes of EEPROM data memory, self-programming, an ICD, 2 Comparators, 8 channels of 10-bit Analog-to-Digital (A/D) converter, 2 capture/compare/PWM functions, a synchronous serial port that can be configured as either 3-wire SPI

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or 2-wire I2C bus, a USART, and a Port.

Fig.3. Embedded unit

RS-232 is the traditional name standards for serial binary single-encontrol signals connecting between Terminal Equipment) and a DCE (terminating Equipment). It is commcomputer serial

Fig.4. RS 232 port

ports. The standard defines thcharacteristics and timing of signals, tsignals, and the physical size anconnectors. An RS-232 serial port feature of a personal computer, used foto modems, printers, mice, duninterruptible power supplies, and otdevices.

ZigBee is a specification for a suitecommunication on protocols using smdigital radios based on an IEEE 802personal area networks. ZigBee [10often used in mesh network form toover longer distances, passing intermediate devices to reach more distallows ZigBee [16] networks to be fowith no centralized control ortransmitter/receiver able to reach all oAny ZigBee device can be tasked witnetwork. ZigBee is targeted at apprequire a low data rate, long battery linetworking.

Parallel Slave

for a series of nded data and a DTE (Data (Data Circuit-

monly used in

the electrical the meaning of nd Pinout of is a standard

for connections data storage, ther peripheral

e of high level mall, low-power

2 standard for 0] devices are transmit data data through tant ones. This

formed ad-hoc, r high-power of the devices. th running the plications that ife, and secure

ZigBee specifies operation [12.4 GHz (worldwide), 915 MHAustralia) and 868 MHz (EuSixteen channels are allocated inwith each channel requiring 5 MThe 2.4 GHz band provides 915 MHz provides up to 40 kprovides a data rate up to 20 kshift keying (BPSK) is used in thbands, and offset quadrature (OQPSK) that transmits two bitsin the 2.4 GHz band. The raw, ois 250 kbit/s per channel in thekbit/s per channel in the 915 MHzin the 868 MHz band. Transmissi10 and 75 meters (33 and 246 fmeters for ZigBee PRO, althodependent on the particular enviro

ZigBee is not intended to networking but to interface with metering and smart appliance ZigBee [20] nodes can go from sin 30 ms or less, the latency cancan be responsive, particulaBluetooth wake-up delays, waround three seconds. 250 kbiperiodic or intermittent data transmission from a sensor Applications include wireleselectrical meters with in-hommanagement systems, and othindustrial equipment that rewireless transfer of data at relatitechnology defined by the ZigBintended to be simpler and less eWPANs, such as Bluetooth.

Fig.5. ZigBee

7] in the unlicensed Hz (Americas and urope) ISM bands. n the 2.4 GHz band, MHz of bandwidth. up to 250 kbit/s,

kbit/s and 868 MHz kbit/s. Binary phase-he 868 and 915 MHz

phase-shift keying s per symbol is used over-the-air data rate e 2.4 GHz band, 40 z band, and 20 kbit/s ion range is between feet) and up to 1500 ough it is heavily onment.

support power line it at least for smart purposes. Because

sleep to active mode n be low and devices arly compared to

which are typically it/s, best suited for or a single signal

or input device. s light switches, me-displays, traffic her consumer and equires short-range ively low rates. The Bee specification is expensive than other

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Fig.6. Receiver side

III. EXPERIMENT METHODOLOGY

Workbench for System Analysis

Fig.7. Experimental setup for the speed and torque analysis.

The workbench was designed to obtain the speed and torque on the motor shaft. Fig. 7 shows its sketch, which consists of a 110-W induction motor with nominal rotation speed of 1500 RPM. A metallic disc was fitted on the output shaft. 2 IR Sensors are used here. The disc on the shaft rotates in between the two IR sensors. Then the signals from the IR sensor are transferred to the embedded unit. The embedded unit processes the signals locally and the speed and torque values are obtained. The obtained values are transmitted to the monitoring unit using ZigBee. A pair of ZigBee module can act as transmitter and receiver.

IV. SIMULATION RESULTS

Plot for speed, torque, output voltage and output current can be obtained. Two cases are considered here. Applying a load of 10 kg and applying a load of 40 kg. As the load increases, the speed reduces. It is shown in the first plot. But as the load increases the torque also increases. It is shown in the second plot. The output voltage and output current for a load of 10 kg is shown in the third plot. Plot for output voltage and output current for a load of 40 kg is shown in the fourth plot. In the fifth plot speed, torque and current values are shown for 10 kg load. Plot for speed, torque and current for 40kg load is shown in the sixth plot.

Fig.8. Plot for Speed

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Fig.9. Plot for torque

Fig.10. Plot for output voltage and output current for

10 kg load

Fig.11. Plot for output voltage and output current for

40 kg load

Fig.12. Plot for speed, torque and current for 10kg load

Fig.13. Plot for speed, torque and current for 40kg load

V. CONCLUSION

This paper presented an embedded system integrated into a ZigBee based wireless sensor network (WSN) for online speed and dynamic torque monitoring in induction motors. Electrical signals from the motors were taken in noninvasive manner and given to the embedded system. The calculations for estimating the targeted values are done locally and then transmitted to a monitoring base unit using ZigBee based wireless sensor network. Speed of deployment, maintenance, low cost, security, reliability and throughput were the main advantages of using ZigBee. Even with the difficulties in data transmission using the WSN in some scenarios, the system was able to provide useful monitoring information. Plot for speed, torque, output voltage and output current are obtained from the simulation for different load values.

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