How do sensors work? I need slightly technical information?

carbon monoxide detectors wiki image

nandiana20

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
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_monoxide_detector

What type of sensors are in a carbon dioxide detector?

I think it has metal oxide semiconductors but I'm not entirely sure...help?

Answer
I expect you mean carbon monoxide. The types are: Opto-Chemical, Biomimetic, Electrochemical and Semiconductor. You are not likely to find one which is opto-chemical. detailed information at en.wikipedia.org/wiki/Carbon_monoxide_detector

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Is there a certain threshold before a carbon monoxide alarm will sound?

carbon monoxide detectors wiki image

sarah

I've noticed my kittie carbon monoxide detector register several times but no alarm ever sounded, is this normal. first time it was 35. i figured the levels might be too low. today it registered over 100 and it never sounded off an alarm. There is no 1800 number i can call them to ask.

Answer
The alarm points on carbon monoxide detectors are not a simple alarm level (as in smoke detectors) but are a concentration-time function. At lower concentrations (eg 100 parts per million) the detector will not sound an alarm for many tens of minutes. At 400 parts per million (PPM), the alarm will sound within a few minutes. This concentration-time function is intended to mimic the uptake of carbon monoxide in the body while also preventing false alarms due to relatively common sources of carbon monoxide such as cigarette smoke.

From WIKI

how can you tell if the burners on the water heater is dirty?

Shakara B

Also how do you know if there is carbon monoxides in your house? what is the symptom's. how long dos it take to kill? is there a way to stop it? where does it come from? can carbon monoxide come from a dryer if the vent don't have one of those medal things? is it safe for a dryer to not have a medal thing on the vent? can carbon monoxide get in the house from the vent

Answer
Carbon Monoxide
Wikipedia: (link : en.wikipedia.org/wiki/Carbon_monoxide ) Carbon monoxide, with the chemical formula CO, is a colorless, odorless and tasteless, yet highly toxic gas. Its molecules consist of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond. It is the simplest oxocarbon, and can be viewed as the anhydride of formic acid (CH2O2).

Carbon monoxide is produced from the partial oxidation of carbon-containing compounds; it forms in preference to the more usual carbon dioxide (CO2) when there is a reduced availability of oxygen, such as when operating a stove or an internal combustion engine in an enclosed space. Carbon monoxide has significant fuel value, burning in air with a characteristic blue flame, producing carbon dioxide. Despite its serious toxicity, it was once widely used (as the main component of coal gas) for domestic lighting, cooking and heating, and in the production of nickel. Carbon monoxide still plays a major role in modern technology, in industrial processes such as iron smelting and as a precursor to myriad products.

EPA : (link) www.epa.gov/iaq/co.html

Have a service man check your hot water heater, to make sure it is burning properly, and VENTING PROPERLY !

Carbon monoxide can only be detected by a CO detector or meter!

You DONâT KNOW!
THATâS THE KILLER PART!
You canât smell or taste it. The only symptom I know of, that may inform you is if you feel sick to your stomach and may up-chuck before passing out â but not always.

As for time to kill, it depends on some factors, co flow, fresh air flow into the area, how near you are to it. ITâS NOT TO BE MESSED WITH, âIF IN DOUBT GET EVERYONE OUTâ AND then CALL 911, for fire rescue.

Only way to stop it is have the unit âprofessionallyâ checked out!
Come from: improper burner settings and improper venting.

Yes! It can come from a dryer if the dryer is GAS, not electric!

What do you mean by âone of those medal thingsâ? Do you mean a flapper door, on the outside of the house, where the vent exits, NO.

Again referring to the above answer âflapper doorâ , that help to keep animals and bugs from entering the house, but it doesnât always work.

Yes, CO can re-enter the house from a vent if the conditions are right. As the burned gas vents outside the wind can carry it back into the house thru an open window!

Hope this helps!
Good Luck!

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