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We are making a smart home safety system for a small academic project (Yes. I am a newbie for this). We need a Gas Sensor (LP Gas) for the project, but there are a few questions that I have.

I found the MQ-6 Sensor that can be used for sensing the LP gas leakage. But the problem is, how far can it go ?

I live in a tropical country, where there is always high temperature and humidity.

  1. How can these weather conditions effect the sensor ?
  2. What happens if we keep it in a large room ? Will it still be able to sense the gas ?
  3. How much closer do I have to place the sensor to the cylinder ?

Any ideas will be helpful. Thanks in advance.

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    I wonder if this is off-topic? Being a demo system seems the best justification for keeping it, if you wanted a production quality answer, I'd suggest electronic engineering SE. – Sean Houlihane Dec 16 '16 at 9:00
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    At which point are trying to detect a leak? At the cylinder or just overall in the room. – Mahendra Gunawardena Dec 30 '16 at 13:00
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    @MahendraGunawardena Well, our requirement was to check any gas leakages and report it immediately. We thought to place it near the gas cylinder. Thanks anyway. – ThisaruG Dec 30 '16 at 13:42
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Regarding the humidity and temperature there are the following specifications that should be match:

environment specifications regarding temperature and humidity of the sensor

Problems will start above 50 °C and 95 % humidity. But below, it should be fine.

The standard detecting conditions are less than the above mentioned values:

table of standard detecting conditions (around 20°C and 65% humidity

They have measured the sensitivity characteristic with these conditions (fig 2 in datasheet) so I strongly recommend to recalibrate the sensor in your own environment if you are able to do such thing.

How can these weather conditions effect the sensor?

graph showing the dependence of the sensor on temperature and humidity

This is the figure you need.

What happens if we keep it in a large room ? Will it still be able to sense the gas?

According to the sensitivity characteristic in the datasheet the minimum concentration is 200 ppm. Now, I do not think that in a large room the air will be homogeneous. So there will be places where the concentration is lower or higher then 200 ppm. Depends on ventilation and the insulation of the building. Check the detectable gas densities compared to the air's density to decide where the sensors should be placed. But always close to the potential gas leakage source. Here is a table about specific gas gravity values but please check some more official sources as well.

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    Last paragraph, 'about' means 'above'? But this is wrong, I think. Should be 'below'. – Sean Houlihane Dec 16 '16 at 9:01
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    I have added correction. It all comes down to density of air and the detectable gas. – Bence Kaulics Dec 16 '16 at 9:01
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    @Sean But yes after checking some tables it seems to be that "below" the correct position. – Bence Kaulics Dec 16 '16 at 9:09
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I've not used one of these sensors, but looking at the quoted sensitivity, it would be best placed as close as possible to the source of a leak, or at a low point (many flammable gasses are denser than air, so they tend to collect in depressions at the floor space. You should not be expecting to demonstrate this particular sensor operating, I think.

An ideal location is on the ground, below the gas pipe or equipment. The gas supply cylinder must be outdoors (at least by our regulations) ...

The sensor is probably more sensitive to humidity than to temperature. High humidity might make it less sensitive, high temperature is likely to damage it (since the sensor itself generates heat to combust the target gas).

If you want to calculate the ppm exposure which you think might be relevant to compare against the sensor data, estimate the leakage rate which you would like to detect (a pin hole, survivable scenario), and guess the gas concentration after 8 hours whilst also factoring in circulation (an open area is harder to detect than the low point inside a boat hull).

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Another area to consider is corrosion in electrical signal paths, particularly in tropical climates close to the ocean. If the metal electrical connections are expose to the elements the conductive medium starts deteriorating cause a change in electrical signal. Therefore good mechanical packaging might be something to consider.

Alternatively, in Tropical climates Liquid Petroleum Gas (LPG) is mostly used for cooking. Also the LPG cylinder tends to be placed close to the stove. So if you can monitor use of the stove in relationship to LPG cylinder pressure, it might be possible to monitor and notify if there is a LP gas leak using something like IFTTT. Example if stove not in use and LP Gas pressure is dropping then there might be a leak and alert interested parties.

Deviating outside the scope of the question, additional services can be created to notify users when LP gas is running low or even monitor usage patterns to help manage LP Gas usage. It is common in under develop countries to carry a secondary small backup gas cylinders to supplement until a availability of a refill. Providing a monitoring capabilities can help eliminate the secondary LP gas cylinder.

References:

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