09-10-2012, 05:42 PM
FOOTSTEP POWER GENERATION
FOOTSTEP POWER GENERATION.doc (Size: 1.95 MB / Downloads: 162)
INTRODUCTION TO PROJECT :
Man has needed and used energy at an increasing rate for his sustenance and well-being ever since he came on the earth a few million years ago. Due to this a lot of energy resources have been exhausted and wasted. Proposal for the utilization of waste energy of foot power with human locomotion is very much relevant and important for highly populated countries like India and China where the roads, railway stations, bus stands, temples, etc. are all over crowded and millions of people move around the clock. This whole human/ bio-energy being wasted if it can be made possible for utilization it will be great invention and crowd energy farms will be very useful energy sources in crowded countries.
Walking is the most common activity in day to day life. When a person walks, he loses energy to the road surface in the form of impact, vibration, sound etc, due to the transfer of his weight on to the road surface, through foot falls on the ground during every step. This energy can be tapped and converted in the usable form such as in electrical form.
In this project the main role is played by piezoelectric sensor. These sensors convert the mechanical energy into electrical energy. This energy is stored in rechargeable battery and this energy is used for operating A.C and D.C.
INTRODUCTION TO SENSOR
What is sensor?
Sensors are sophisticated devices that are frequently used to detect and respond to electrical or optical signals. A Sensor converts the physical parameter (for example: temperature, blood pressure, humidity, speed, etc.) into a signal which can be measured electrically. Let’s explain the example of temperature. The mercury in the glass thermometer expands and contracts the liquid to convert the measured temperature which can be read by a viewer on the calibrated glass tube.
Criteria to choose a Sensor:
There are certain features which have to be considered when we choose a sensor, They are
1.Accuracy
2.Environmental condition - usually has limits for temperature/ humidity.
3.Range - Measurement limit of sensor.
4.Calibration-Essential for most of the measuring devices as the readings changes with time.
5.Resolution - Smallest increment detected by the sensor.
6.Cost.
7.Repeatability-The reading that varies is repeatedly measured under same environment.
Definition:
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, all sensors need to be calibrated against known standards. ( OR )
Sensor is the device which converts any physical quantity to its equivalent electrical signal. There are different types of sensor are available there are: Temperature sensor, Light sensor, Voltage sensor, Smoke Sensor, Gas sensor, Fire sensor, Magnetic Sensors, etc.
Classification of measurement errors :
A good sensor obeys the following rules :
• Is sensitive to the measured property
• Is insensitive to any other property likely to be encountered in its application
• Does not influence the measured property
Ideal sensors are designed to be linear or linear to some simple mathematical function of the measurement, typically logarithmic. The output signal of such a sensor is linearly proportional to the value or simple function of the measured property. The sensitivity is then defined as the ratio between output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is a constant with the unit [V/K]; this sensor is linear because the ratio is constant at all points of measurement.
Sensor deviations :
If the sensor is not ideal, several types of deviations can be observed:
The sensitivity may in practice differ from the value specified. This is called a sensitivity error, but the sensor is still linear.
Since the range of the output signal is always limited, the output signal will eventually reach a minimum or maximum when the measured property exceeds the limits. The full scale range defines the maximum and minimum values of the measured property.
If the output signal is not zero when the measured property is zero, the sensor has an offset or bias. This is defined as the output of the sensor at zero input.
If the sensitivity is not constant over the range of the sensor, this is called nonlinearity. Usually this is defined by the amount the output differs from ideal behavior over the full range of the sensor, often noted as a percentage of the full range.
If the deviation is caused by a rapid change of the measured property over time, there is a dynamic error. Often, this behavior is described with a bode plot showing sensitivity error and phase shift as function of the frequency of a periodic input signal.
If the output signal slowly changes independent of the measured property, this is defined as drift (telecommunication).
Long term drift usually indicates a slow degradation of sensor properties over a long period of time.
Noise is a random deviation of the signal that varies in time.
Hysteresis is an error caused by when the measured property reverses direction, but there is some finite lag in time for the sensor to respond, creating a different offset error in one direction than in the other.
If the sensor has a digital output, the output is essentially an approximation of the measured property. The approximation error is also called digitization error.
If the signal is monitored digitally, limitation of the sampling frequency also can cause a dynamic error, or if the variable or added noise noise changes periodically at a frequency near a multiple of the sampling rate may induce aliasing errors.
The sensor may to some extent be sensitive to properties other than the property being measured. For example, most sensors are influenced by the temperature of their environment.
All these deviations can be classified as systematic errors or random errors. Systematic errors can sometimes be compensated for by means of some kind of calibration strategy. Noise is a random error that can be reduced by signal processing, such as filtering, usually at the expense of the dynamic behavior of the sensor.
Resolution :
The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved. The resolution is related to the precision with which the measurement is made. For example, a scanning tunneling probe (a fine tip near a surface collects an electron tunneling current) can resolve atoms and molecules.