SUBMITTED BY
MR.DEVSATWAR P.R.
&
MR.BHAWARE M.S.

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ABSTRACT
The main aim of the project work is for monitoring the load current continuously and to protect the electrical gadgets burning due to the over load. This kind of control systems are quite suitable for the industries, where the heavy loads like induction motors, ovens, furnaces, broilers, etc., can be protected from the over loads. Using this type of load breakers, the conventional mechanical fuses can be avoided. The same control system also can be used for domestic applications. Now a days, we find lot of household electrical gadgets are burning because of load variations. Hence, the load monitoring and control system become an essential requirement to safeguard the electrical gadgets.
In this system for monitoring the load current, CT (current transformer) is used and its primary is connected in series with the load. The voltage induced at primary is directly proportional to the load current. The output of this CT is converted into DC using rectifier and filter, and this analog output from the CT is fed to the analog to digital converter for converting in to digital pulses. The digital information or digitalized data from the A-D converter is fed to the micro-controller unit for taking the necessary action according to the received information. Here, the micro-controller plays a vital role. The micro-controller compares the value of parameter with defined program, if it goes beyond the preset value, then it takes relative action.
The parameter selected in this project work is basic and important industrial parameter, which needs continuous check-up. For this purpose, this parameter value to be monitored and displayed. Therefore, a digital display of 2 digits is provided at the output of the micro-controller for displaying the current flowing through the CT primary.
The output of micro-controller is used to drive the electro magnetic relay. Whenever the load current exceeds its preset value immediately. The micro-controller energizes the relay. This relay contact is used to break the supply to the load. In addition to the relay, an alarm of 12V DC buzzer is also connected at the output of the micro-controller, which energizes automatically, if the load exceeds its limit. There by, on receipt of danger signal, timely action can be taken and severe damages can be avoided.
INTRODUCTION
In this project work Micro-controller is used for monitoring and control the load parameter. Controllers are increasingly being used to implement control systems. It is therefore important to under stand micro-controller performs controlled system well. This project report describes about the design and development of “Load monitor and Breaker with Digital Display using Micro-controller”.
Nowadays with the advancement of technology in the field of micro-controllers, all the activities in our day-to-day living have become part of information technology and we find controllers in each and every application.Thus, the trend is directing towards micro-controller based project works. However in this project work, the basic signal processing of load parameter is monitored with analog circuit. The output of the parameter is fed to A/D converter for converting the analog information in to digital information.
A micro-controller contains a CPU, clock circuitry, ROM, Ram and I/O circuitry on a single integrated circuit package. The Micro-controller is therefore, a self-contained device, which does not require a host of associated support chips for its operation as conventional microprocessors do. It offers several advantages over conventional multi-chip systems. There is a cost and space advantage as extra chip costs and printed circuit board and connectors required to support multi-chip systems are eliminated. The other advantages include cheaper maintenance, decreased hardware design effort and decreased board density, which is relevant in portable control equipment.
Low cost high volume products requiring a relatively simple and cheap computer controller have traditionally characterized micro-controllers. The design optimization parameters require careful consideration of architectural tradeoffs, memory design factors, instruction size, memory addressing techniques and other design constraints with respect to area and performance. Micro-controllers functionality, however, has been tremendously increased in the recent years. Today, one gets micro-controllers, which are stand alone for applications in data acquisition system and control. With the help of analog-to-digital converts, provided at the input of micro-controller, enables them direct use in instrumentation. Another type of micro-controller has on-chip communication controller, which is designed for applications requiring local intelligence at remote nodes and communication capability among these distributed nodes. Advanced versions of the micro-controller in 16-bit configuration have been introduced for high performance requirements particularly in applications where good arithmetical capabilities are required. In this project work ATMEL 89C51 micro-controller is used, this is 8-bit micro-controller and it is playing a major role in this project work.
The purpose of this project work is to present control theory that is relevant to the analysis and design of micro-controller based controlled systems, with an emphasis on basic concepts and ideas. It is assumed that a digital controller with reasonable software is available for computations and simulations so that many tedious details can be left to the controller. The control system design is also carried out up to the stage of implementation in the form of controller programs in a high level language. One can view micro-controller based controlled systems as approximations of analog control systems, but this is a poor approach because the full potential of micro-controller control is not used. At best the results are only as good as those obtained with analog control.
The micro-controller-controlled system contains essentially four parts, i.e., the process, the analog to digital converter, the control algorithm, and the clock. The times when the measured signals are converted to digital form are called the sampling instants; the time between successive samplings is called the sampling period and is denoted by h. The output from the process is a continuous time signal. The output is converted into digital form by the A – D converter. The A – D converter can be included in the micro-controller or regarded as a separate unit, according to ones preference. The conversion is done at the sampling times. The micro-controller interprets the converted signal, as a sequence of numbers, processes the measurements using an algorithm, and gives a new sequence of numbers. This sequence is converted to an analog signal by a digital to analog converter. The micro-controller operates sequentially in time and each operation takes sometime. The micro-controller -controlled system contains both continuous time signals and sampled, or discrete time, signals such systems have traditionally been called sampled data systems, and this term will be used here as a synonym for micro-controller- controlled systems.
The mixture of different types of signals sometimes causes difficulties. In most cases it is, however sufficient to describe the behavior of the system at the sampling instants. The signals are then of interest only at discrete times. Such systems will be called discrete time systems. Discrete time systems deal with sequence of numbers, so a natural way to represent these systems is to use difference equations.
In this project work, the program is written in ‘Assembly’ language and facilitates the display of current flowing through the current transformer primary. The most fundamental parameter of an industry is load. Monitoring and control of load current consumed by any oven, furnace, broiler, etc; (normally belongs to an Industry) is very essential, otherwise; other wise these machines may burn because of over loads.
For measuring the current consumed by the load, current transformer is used. Here the transducer is current transformer; basically this is nothing but step up transformer. The primary of the transformer is connected in series with the load and the current flowing through.
BLOCK DIAGRAM AND BRIEF DESCRIPTION
The block diagram of the project work “Load monitor and Breaker with Digital Display using Micro-controller” is explained in this chapter. The complete block diagram of the project work is shown at the end of this chapter, for better understanding the total block diagram is divided in to various blocks, and each block explanation is provided in this chapter. The detailed description of each block is as follows.
LOAD CURRENT SENSING CIRCUIT
The current transformer is used with its primary winding connected in series with line carrying the current to be measured and, therefore, the primary current is dependant upon the load connected to the system and is not determined by the load (burden) connected on the secondary winding of the current transformer. The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. The secondary winding of the current transformer has larger number of turns, the exact number being determined by the turn’s ratio. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. Thus a current transformer operates its secondary winding nearly under short circuit conditions. One the terminal of the secondary winding is earthed so to protect equipment and personnel in the vicinity in the even of an insulation breakdown in the current transformer.
The output of the CT after converting AC into DC is fed to A/D converter. The output of the CT will vary according to the load current flowing through this CT primary and this variable voltage is converted into digital pulses and this digital information is fed to micro-controller which energize the relay automatically whenever the load current exceeds its preset value.
For sensing the load current, a current transformer is used as load sensor, which is connected in series with the load. For the demonstration purpose, for monitoring the load current, the Ac lamp load is simulated in the project work. Basically the current transformer is a step-up transformer. The amplifier secondary AC signal is rectified and filtered by using a half wave rectifier and filter. They’re by the DC voltage output proportional to the current flowing through the primary of the CT, which is nothing but the load current.
CLOCK GENERATOR
The clock generator circuit is designed using 555 Timer IC. This IC is configured in Astable Mode of operation (free running oscillator). The frequency can be adjusted using external resistor and capacitor. The required frequency is more than 100KHz. The output of this IC is fed to the A - D converter.
Analog to Digital Converter
As the peripheral signals usually are substantially different from the ones that micro-controller can understand (zero and one), they have to be converted into a pattern which can be comprehended by a micro-controller. This task is performed by a block for analog to digital conversion or by an ADC. This block is responsible for converting an information about some analog value to a binary number and for follow it through to a CPU block so that CPU block can further process it.
This analog to digital converter (ADC) converts a continuous analog input signal, into an n-bit binary number, which is easily acceptable to a computer.
As the input increases from zero to full scale, the output code stair steps. The width of an ideal step represents the size of the least significant Bit (LSB) of the converter and corresponds to an input voltage of VES/2n for an n-bit converter. Obviously for an input voltage range of one LSB, the output code is constant. For a given output code, the input voltage can be any where within a one LSB quantization interval.
An actual converter has integral linearity and differential linearity errors. Differential linearity error is the difference between the actual code-step width and one LSB. Integral linearity error is a measure of the deviation of the code transition points from the fitted line.
The errors of the converter are determined by the fitting of a line through the code transition points, using least square fit, the terminal point method, or the zero base technique to provide the reference line.
A good converter will have less than 0.5 LSB linearity error and no missing codes over its full temperature range. In the basic conversion scheme of ADC, the un-known input voltage VX is connected to one input of an analog signal comparator, and a time dependant reference voltage VR is connected to the other input of the comparator.
In this project work ADC 0809 (8 Bit A/D converter) is used to convert an analog voltage variations (according to the condition of the parameters) into digital pulses. This IC is having built in multi-plexer so that channel selection can be done automatically.
MICRO-CONTROLLER
Micro-controller unit is constructed with ATMEL 89C51 Micro-controller chip. The ATMEL AT89C51 is a low power, higher performance CMOS 8-bit microcomputer with 4K bytes of flash programmable and erasable read only memory (PEROM). Its high-density non-volatile memory compatible with standard MCS-51 instruction set makes it a powerful controller that provides highly flexible and cost effective solution to control applications.
Micro-controller works according to the program written in it. The program is written in such a way, so that the output from the ADC will be converted into its equivalent voltage and based on the magnitude of the voltage, it calculates the parameter value. Now this magnitude is again digitalized and fed to 7-segment display unit through the latch.
Micro-controllers are "embedded" inside some other device so that they can control the features or actions of the product. Another name for a micro-controller, therefore, is "embedded controller". Micro-controllers are dedicated to one task and run one specific program. The program is stored in ROM (read-only memory) and generally does not change Micro-controllers are often low-power devices. A battery-operated Micro-controller might consume 50 milli watts. A micro-controller has a dedicated input device and often (but not always) has a small LED or LCD display for output. A micro-controller also takes input from the device it is controlling and controls the device by sending signals to different components in the device