How do sensors work? I need slightly technical information?

Question

I'm doing this paper on wireless monitoring and I really need to know how sensors basically work and more specifically how temperature ,pressure ,light,radiation, force and toxic gas sensors work. I'm not an electronics student. So an extremely simple explanation would be helpful.

Answer 1

You are asking for a lot of technical information.

Temperature sensors alone come in different types. A thermocouple generates a low voltage (millivolts) that is accurately proportional to the temperature difference between two points. A semiconductor sensor uses a specially calibrated diode whose VF voltage is an accurate 2 mV per degree C. It is usually combined with an op-amp circuit to bias it correctly and buffer the voltage.

.  

Answer 2

It is a HUGE field, so you will have to do some web searching. Manufacturers pages are usually good places to find explanatory info.

Temperature:

Thermocouple - makes use of the fact that a junction of 2 different metals produces a voltage difference which varies with temperature.

Thermistor - a resistor whose value changes with temperature. There are 2 types, PTC and NTC, positive / negative temperature coefficient.

Pressure:

Typically you have a silicon membrane with a force sensor (strain gauge) on it. Pressure on one side of the membrane causes it to distort, which causes a change in resistance in the sensor.

Light:

Photodiode - a diode that leaks current according to how much light falls on it.

Light-dependant resistor (LDR) - does what it says!

Radiation:

Ionisation type detectors - basically a gas-filled tube. When a radiation particle strikes a gas atom it creates an ion, or charged atom. An electric field attracts the ion to a plate, where it is detected as a pulse of current.

Scintillation detector - use a crystal that produces a flash of light when struck by a particle. The flas is detected by a light sensor.

Force:

Strain gauge - a thin film of resistive material. Resistance changes when it is flexed.

Force sensing resistor (FSR) - resistance changes when squeezed

Piezoelectric bimorph - produces a voltage when flexed

Toxic gas:

Carbon monoxide detectors...

http://en.wikipedia.org/wiki/Carbon_mono...

Answer 3

Sensors work in several different ways.

Light sensors use a circuit with a CdS eye or a photodiode as the active components.  There will necessarily be some resistors and perhaps other components involved as well.

Temperature sensor CAN use several small diodes hooked in series.

Pressure sensors use a device called a strain guage...Which is merely a thin piece of silicon material with wires attached that can be GLUED to a surface and sense the 'bend' caused by pressure.

Radiation can be sensed by a tube containing an inert gas, with two elements, one charged VERY high voltage.  When a particle hits the tube, it ionises the inert gas and causes the two elements to conduct briefly.

Force can be sensed by a pendulum attached to a strain guage.

Toxic gases are sensed by a circuit called ' hot wire'...where two wires carrying a tightly calibrated current, one exposed to the gas being sensed, one sealed.  The current differences are compared to sense the gases.  Spectroscopy can also be used, where the gas is heated till it glows, then the light is run thru a spectroscope.

ALL of these sensors cause a change in a current and/or a voltage which must be measured using a meter, or analog to digital converter connected to a computer.

Hope this helps

Answer 4

A volume control on music turns sound up and down; the room temperature change causes a similar change in an electrical circuit which is passed along to appropriate displays.  

Pressure works along the same lines as temperature causing a voltage or resistance to change with changes in pressure.

Light monitoring uses photo-electric transducers, components that will exhibit a voltage change when the intensity of light changes.

Monitoring of Radiation uses a comparator circuit, a known small source and anything above that level sends a voltage difference to be displayed.

Force is monitored through quartz crystals that will have a voltage change when stressed.

Toxic gas monitoring generally uses a source radiation as a comparator, when the air in the sample chamber has impurities from the "norm" it, through amplification will show a change

Answer 5

temperature can be measured by a bilame, pressure by a membrane comtaining comductor forming some kind of rehostat, light by photocells as well as radiations, forse by a bobine containing soft iron, toxic gaz by chemical solvant...There is too amny sensors but those are some examples