Gases don't have a conductivity. They have a break-down voltage instead, and any break-down is likley to cause ignition! Good, positive detection!!

http://www.hse.gov.uk/pubns/gasdetector.pdf

Thank u for ur reply brother.. If gas spread on semiconductor( Sensor), the electrical conductivity of that semiconductor varies ( up/ Down)... depends upon that we conclude the concentration of gas...

<...Brother...>

How abstruse.

See #2↓.

Wiki gives a good explanation....

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

http://www.mindkits.co.nz/store/sensors/hydrogen-gas-sensor-mq-8

"

A relatively well developed technology for the detection of such combustible species in air is the use of a heated noble metal filament, typically Pt, the temperature of which increases when combustion occurs on its surface. A slightly more complex variation of this device is known as a "pellistor": the Pt wire is embedded in a high-surface-area ceramic pellet, which may itself contain catalytic metal particles. With any of these devices, the change in filament resistance resulting from a temperature increase due to combustion on the filament or pellet surface is detected to indicate the presence and concentration of combustible gases."

http://www.sandia.gov/mstc/MsensorSensorMsystems/MicroCombustGasDetect.html

Thank u brother... Give some idea for circuit

Why are you going, "to develop H2 gas sensor", when you can purchase one?

Is this an exercise for a class, or do you really intend to, "develop H2 gas sensor" for some specific application?

Some explaionation, please, because one does not normally just decide, "to develop H2 gas sensor" on a lark for something to do.

Not only that, what is the environment at which this sensor is supposed to operate?

Are we talking about 1 atmosphere or vacuum? What other gasses will be present?

At what temperature is the probe going to operate? Will the probe be in contact with the hydrogen or must it be detected at a distance?

One of the first things an engineer must do is to ask enough questions to narrow down the range of practical answers. A specifier must learn to communicate his specifications well enough so that a million questions won't need to be asked.

1.

. . .

15.

16. Did you look at SolarEagle's #6?

17. Are you trying to differentiate hydrogen from other combustible gases, or are you really looking for combustible gas detector?

18. What's your name?

19. Who's your daddy?

20. Is he rich?

Hai friends, am engineering graduate,. Am decide to develope h2 gas sensor., For avoid explotion during battery charging and various application.. Initially am decide to purchase h2 sensor and make a circuit for that one.. If that one give success for us means i like to fabricate the h2 sensor by own..

Please make sure that all CR4 readers are out of the area before you switch it on, Mildred. I wouldn't want to be mixed up if it sets off the hydrogen in a major detonation!

Why don't you just do the charging in a well-ventilated place, like outdoors?

Please be aware that while hydrogen gas does build up when charging lead acid batteries (for example), the amount of Hydrogen is quite small and only becomes dangerous in an enclosed space after an extended period of charging (or overcharging).

The common method of preventing this is to provide venting to the battery compartment, and even a little venting will prevent dangerous buildup and hence remove the danger.

This sounds like an application looking for a problem that doesn't really exist (at least in the battery charging market, large battery arrays may be a good market but I believe there are existing Hydrogen detection products on the market you would be competing with).

Have you looked on the internet regarding similar existing Hydrogen detection products, designs and applications?

Also, if the Hydrogen builds up to a dangerous level then your circuit electronics could inadvertently cause an explosion (as others have mentioned), so also have a look on the internet regarding Hydrogen gas upper and lower explosion limits so you can set the Hydrogen detection levels to those below and/or above the explosion limits of the gas mixture concentration.

Good luck.

You seem very determined...

What prompted you to make this decision?

Perhaps you are not aware of regulations requiring testing before a product like this can be sold on the open market. In some cases, such as a hydrogen sensor, you must prove that your sensor can not ignite the hydrogen thereby causing a bad accident. Your would have to pay for all of the testing required to sell that sensor.

I could not begin to tell you who all the authorities are that would have to approve your design, but they are likely related to the fire department. In the United States, the National Electrical Code was originally written by the Fire Department because they had to put out the fires.

my post may be make laugh to you., sorry

There's an American saying that I think fits.

Don't bit off more than you can chew.

I'd think you'd want to design your own circuits. That's electrical engineering.

Designing a safe sensor to operate in an extremely hazardous environment involves materials, mechanical and safety engineering.

Hit those books, you've got a long way to go.