02-05-2011, 11:04 AM
[attachment=13205]
1. INTRODUCTION
The project “Automated Electricity Meter” aims to move away from the traditional method of manual reading of electricity meters in which an individual has to physically record the reading. Instead the project proposes to successfully be able to take the meter reading automatically without having a person be physically present while taking the reading, thereby reducing manpower requirement. As the project name suggests, the vision of our project is to create an automated environment for the purpose of meter readings and thus reduce the dependency on human resources. Thus the ‘Automated meter’ would be the representative of the company for the purpose of taking readings without involving human error.
1.1 BACKGROUND
1.1.1 DESCRIPTION OF ELECTRIC METER
An electric meter or energy meter is a device that measures the amount of electrical energy consumed by a residence, business organisation, or an institution.
Electric meters are typically calibrated in billing units, the most common one being the kilowatt hour. Periodic reading of electric meters establishes billing cycles and energy used during a cycle.
When energy savings during certain periods are desired, meters may measure demand, the maximum use of power in some interval. In some areas, the electric rates are higher during certain times of day, to encourage reduction in use. Also, in some areas meters have relays to turn off nonessential equipment.
1.1.2 PROBLEMS ASSOCIATED WITH CONTEMPORARY METERS
Even though the contemporary meters are widely used, there are many shortcomings associated with it, viz.
1. Inefficient use of Labour force
In today’s time when skilled labour force is limited not easily and cheaply available, it is highly impractical and not cost effective for electrical energy supplying companies to employ human resources for just collecting reading from various individual consumers.
2. Indication of Short Circuits
Contemporary meters are incapable of indicating any kind of short circuit or any other mishappenings with the meter.
3. Faulty Meter readings
Many a times, due to human shortcomings it so happens that the meter readings get interchanged at the time of reading and the consumer is charged for the electricity he hasn’t used. This may also take place intentionally due to personal grudges and avarice.
4. Time Consuming
Since the entire process requires human force to be present at each of the remote location to record the reading and hence it is time consuming.
1.2 ELECTRICAL POWER MEASUREMENT
Power (P) is a measure of the rate of doing work or the rate at which energy is converted. Electrical power is the rate at which electricity is produced or consumed. Electric power is the combination of the water pressure (voltage) and the rate of flow (current) that results in the ability to do work. Electrical power is defined as the amount of electric current flowing due to an applied voltage. It is the amount of electricity required to start or operate a load for one second. Electrical power is measured in watts (W).
Electrical energy introduces the concept of time to electrical power. In the water analogy, it would be the amount of water falling through the pipe over a period of time, such as an hour. When we talk about using power over time, we are talking about using energy. Using our water example, we could look at how much work could be done by the water in the time that it takes for the tank to empty.
The electrical energy that an appliance or device consumes can be determined only if you know how long (time) it consumes electrical power at a specific rate (power). To find the amount of energy consumed, you multiply the rate of energy consumption (measured in watts) by the amount of time (measured in hours) that it is being consumed. Electrical energy is measured in watt-hours (Wh).
One watt-hour is a very small amount of electrical energy. Usually, we measure electrical power in larger units called kilowatt-hours (kWh) or 1,000 watt-hours (kilo = thousand). A kilowatt-hour is the unit that utilities use when billing most customers.
Energy (E) = Power (P) x Time (t)
E = W x h = Wh
The number of units consumed by a 60 W bulb for a month for a average residential unit in an metropolitan city is 15. Considering the overall consumption of the residential unit to vary anywhere between 100 to 300, the amount to be payed by the consumer to the energy supplier only for a 60 W bulb is
Amount= 15*5.56
= 83.4
1.3 AUTOMATED METER
An automated meter, is an advanced meter (usually an electrical meter) that records consumption at all instants and communicates the reading information via wireless network back to the central system for monitoring and billing purposes (telemeter) as per the requirement and regulation of the energy supplier . It enables two-way communication between the meter and the central system.
BLOCK DIAGRAM
The above figure shows the block diagram of the automated electricity meter which consists of a central system and individual meters. The individual meters and the central system communicate with each other via a wireless network.
1.3.1 FUNCTION OF METER BLOCKS:
The meter records the consumption of electrical energy of a particular institution such as a household or an industry. It contains the meter readings of the previous twelve months and can transmit the recorded readings whenever required by the Central System.
1.3.2 FUNCTIONS OF THE CENTRAL SYSTEM:
The Central System is the master of all the meters in the network and controls their operations. It issues various signals to the meters connected in the network to which they reciprocate by transmitting the required data.
1.3.3 COMMUNICATION PROCESS:
The process is a duplex communication system. The individual meters respond to the different signals issued by the central system by deciphering them.
The different signals issued by the central system have a unique combination code.
For each combination, the meters act accordingly and transmit the required data.
00: This code is broadcasted at the end of the billing period. On receiving this signal the meters send their recorded reading one at a time. After transmitting the reading, the meter counter is reset.
01: When ’01’ is transmitted by the central system, the meter on receiving the code sends the meter reading of the same month but of the previous year.
10: When ‘10’ is transmitted by the central system, the meter receives the signal and transmits the current meter reading which indicates the number of units of electricity consumed. However, the meter counter is not reset and continues to measure the power usage from the same reading.
11: Whenever the energy supplier wishes to stop the operation of the meter , the central system will transmit a ‘11’ code. On receiving this code, the meter stops all operation and shuts down.
Like the central system, the meter also sends signals to the central system via the wireless network.
1: Whenever there is a short circuit scenario, the meter would inform the central system by transmitting a ‘1’ code.
2. REVIEW OF LITERATURE
2.1 ATMEGA 32:
The ATmega32 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC Architecture. By executing powerful instructions in a single clock cycle, the ATmega32 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.
The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers.
2.1.1 Features of Atmega32:
• High-performance, Low-power AVR® 8-bit Microcontroller
• Advanced RISC Architecture
– 131 Powerful Instructions – Most Single-clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 16 MIPS Throughput at 16 MHz
– On-chip 2-cycle Multiplier
• High Endurance Non-volatile Memory segments
– 32K Bytes of In-System Self-programmable Flash program memory
– 1024 Bytes EEPROM
– 2kB Internal SRAM
– Write/Erase Cycles: 10,000 Flash/100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C
– Byte-oriented Two-wire Serial Interface
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
• Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated RC Oscillator
– External and Internal Interrupt Sources
– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby
and Extended Standby
• I/O and Packages
– 32 Programmable I/O Lines
– 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF
• Operating Voltages
– 2.7 - 5.5V for ATmega32L
– 4.5 - 5.5V for ATmega32
• Speed Grades
– 0 - 8 MHz for ATmega32L
– 0 - 16 MHz for ATmega32
• Power Consumption at 1 MHz, 3V, 25°C for ATmega32L
– Active: 1.1 mA
– Idle Mode: 0.35 mA
– Power-down Mode: < 1 μA
2.1.2 PIN CONFIGURATION AND DESCRIPTION:
VCC: Digital supply voltage
GND: Ground
PORT A (PA7..PA0) : Port A serves as the analog inputs to the A/D Converter.
Port A also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. Port pins can provide internal pull-up resistors (selected for each bit). The Port A output buffers have symmetrical drive characteristics with both high sink and source capability. When pins PA0 to PA7 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes active, even if the clock is not running.
PORT B (PB7..PB0): Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running.
PORT C (PC7..PC0): Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port C output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset condition becomes active, even if the clock is not running. If the JTAG interface is enabled, the pull-up resistors on pins PC5(TDI), PC3(TMS) and PC2(TCK) will be activated even if a reset occurs. The TD0 pin is tri-stated unless TAP states that shift out data are entered.
PORT D (PD7..PD0): Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port D output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset condition becomes active, even if the clock is not running.
RESET: Reset Input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running. Short pulses are not guaranteed to generate a reset.
XTAL1: Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
XTAL2: Output from the inverting Oscillator amplifier.
AVCC: AVCC is the supply voltage pin for Port A and the A/D Converter. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.
AREF: AREF is the analog reference pin for the A/D Converter.
2.1.3 USART
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a highly flexible serial communication device.
The main features are:
• Full Duplex Operation (Independent Serial Receive and Transmit Registers)
• Asynchronous or Synchronous Operation
• Master or Slave Clocked Synchronous Operation
• High Resolution Baud Rate Generator
• Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits
• Odd or Even Parity Generation and Parity Check Supported by Hardware
• Data OverRun Detection
• Framing Error Detection
• Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter
• Three Separate Interrupts on TX Complete, TX Data Register Empty, and RX Complete
• Multi-processor Communication Mode
• Double Speed Asynchronous Communication Mode
2.1.4 FRAME FORMAT
A serial frame is defined to be one character of data bits with synchronization bits (start and stop bits), and optionally a parity bit for error checking. The USART accepts all 30 combinations of the following as valid frame formats:
o 1 start bit
o 5, 6, 7, 8, or 9 data bits
o no, even or odd parity bit
o 1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next data bits, up to a total of nine, are succeeding, ending with the most significant bit. If enabled, the parity bit is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it can be directly followed by a new frame, or the communication line can be set to an idle (high) state.
