basic fundamentals of sensors?
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what sort of sensors are u interested in. if it is light then it can be measured using photoconductive or ptotovoltaic devices.
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Here is a good article. To understand them, you need to get a multimeter, and electronics projects book, a breadboard (to mount circuits on), and a selection of electronic parts from Radio Shack. Use batteries initially, and then when you are more confident a power supply and rectifier to do experiments, and measure voltage, current, and resistance values around the circuit.\nhttp://en.wikipedia.org/wiki/Electronics\nHyperphysics. (Google)\nhttp://www.mathworld.wolfram.com\nhttp://www.refdesk.com\n"You can do it electronics," Needham Heights, MA\nEnjoy!
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Howstuffworks has good diagrams and explanations that may help you.  Good luck.
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Temperature measurement
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The links on this site may help: http://en.wikipedia.org/wiki/Radar_detector
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www.ece.rochester.edu/users/hrk1/FPS.htm\nwww.freepatentsonline.com/4577345.html\nmedia.mit.edu/resenv/classes/MAS965/readings/singlechipfingerprint.pdf\nMIKE
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I found 1 here.\nhttp://katz.ws/search/embedded+systems
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You should choose something you could actually finish, so keep it simple.  One project that you could finish and possibly sell copies to friends and family: a digital thermometer and relative humidity sensor.  Everyone wants to know the temperature.  The problem with the relative humidity sensor is that the sensor is not linear from 0-100%RH, so there is error.  Using a PIC microcontroller you can write a software correction program that will correct the sensor output (the thermometer can have the same problem).  Depending on how much math background you may have, this could be an easy or difficult project.  The upside is that you may be able to commercialize the product.  We've done projects with silicon pressure diaphragms correcting for pressure and temperature error (requires a matrix solution leading to polynomial coefficients and a lookup table) - it took years however, so keep the project simple.
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A very good question -- in my experience the key to good control is placement and mass of the temperature sensor.\n\nYou can use a thermocouple or an RTD (resistance temperature device) depending on your temperature range.\n\nBut in most factory process controls the biggest problem is how to make sure that the sensor is measuring the ambient temperature, or the temperature of the object being heated. If any radiant heat energy falls on the sensor, you will get meaningless temperature readings.\n\nIn some cases a simple reflective shield will allow the sensor to measure the ambient temperature.\n\nSometimes the sensor is embedded in either the object or in a dummy object with similar characteristics. After all your goal is to control the RIGHT temperature, not just any temperature.\n\nThe sources below give a typical easy to use PID controller and a high power SSR.\n\nThe controller has an autotune function -- this is very key because tuning a PID controller can be very frustrating. You can end up with wildly cycling kooky results unless you are experienced.\n\nRemember that a Proportional Integrating Controller is a big step up from a bang-bang on off relay type controller. \n\nProportional just means that it can send a small milliamp signal to the Solid State Relay allowing it to proportionally adjust the heat output of your resistance heaters.\n\nIntegrating can be interpreted to mean that the PID takes into account the amount of heat you have already pumped into the system. So it can avoid shooting a big pulse of heat into an oven which it already knows is pretty fired up already.\n\nAnd Derivative means it watches the rise or fall of the temperature curve to prevent overshooting and undershooting. This keeps the temperature from varying wildly. Maybe! Depends on if you know how to tune it.\n\nGive these folks a phone call, they offer free application consulting, even for small projects.
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Here's a study guide.  http://www.doctronics.co.uk/meter.htm
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try netdetective.  that sight is reliable.
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Every gas has a unique breakdown voltage – the electric field at which it is ionized – and ionization sensors identify gases by measuring these voltages. The concentration of the gas can be determined by measuring the current discharged in the device. However, existing sensors are bulky, consume lots of power and require “risky” high voltages to operate.\n\nThe researchers also found that the current discharged in the device was six times higher than in conventional electrodes, which makes the detector highly sensitive. It is able to detect concentrations of gas as low as 10-7 moles per litre. Moreover, it can distinguish between different gases in a mixture and is not affected by external factors such as temperature or humidity – unlike previous detectors. \n\nGas-analysis vacuum sensors are virtually quadrupole mass spectrometers, with which the molecular density of a gas components and the equivalent partial pressure can be determined. The density of the gas composition can be then easily translated into total pressure.\n\nand believe me the smoke sensors works almost same as these gas detectors so plz refer to the article below
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http://www.willamette.edu/~fthompso/MgmtCon/Control_Systems.html\n\n\nhttp://www.isd.mel.nist.gov/documents/falco/ITSecurityProcess.pdf#search='applications%20of%20digital%20control%20systems%20on%20different%20industries'\n\nhttp://www.cs.uidaho.edu/~krings/publications/SACT-2002-D.pdf#search='digital%20control%20systems%20in%20pipelines'\n\nTry them...
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Try theese sites\n\nhttp://www.web-ee.com/primers/Tutorials.htm\nhttp://www.maintenanceresources.com/productsshowcase/productlisting/electronicspage.htm\nhttp://class.ee.iastate.edu/rmander/ee201rma/
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(m)\n\nA detection device that requires input energy from a source other than that which is being sensed. Note: An example of an active sensor is a photoconductive cell. 2. In surveillance, a detection device that emits energy capable of being detected by itself. Note: An example of an active sensor is a measuring instrument that generates a signal, transmits it to a target, and receives a reflected signal from the target. Information concerning the target is obtained by comparison of the received signal with the transmitted signal. 3. A measuring instrument in the Earth exploration-satellite service or in the space research service by means of which information is obtained by transmission and reception of radio waves.
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orbital surveillance/tracking sensor system
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well for my physics project for the boards i made a photoelectronic burglar alarm- at the heart of this was an LDR( Light Dependent Resistor) when the beam of light is obstructed (think laser in the movies-lol) the LDR resistance rises and the circuit inside is set into oscillation and the alarm sounds- other good projects would be a rain alarm, a rectifier, an electroscope,..... the possiblities are endless- i suppose you could do anything involving electric circuits since thats what the cbse calss 12 physics text covers most- i doubt ud want to do anything on ray or wave optics