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7

According to this paper in 2000 (could have changed in 15 years!) there were no commercial sensors on the market specially built for this. However, the following were tested: Figaro sensor type most sensitive to: TGS2600 general air contaminants TGS2610 general hydrocarbons TGS2611 ...


4

No. A flammable gas sensor can be made by heating a wire and measuring its resistance. If that resistance increases, you know that its temperature has increased. Want to guess why the temperature increased? If your guess is correct, you will understand that failure to heat the wire will result in failure to initiate the chemical reaction - combustion - and ...


4

Typically that's stainless-steel mesh. I suggest an inexpensive (many of them come from Pakistan or India) set of dental picks, just hook it where it got bashed in and gently try to pull it out. They are quite useful tools to have around anyway. If this is a combustible gas detector, keep in mind that part of the purpose of the mesh is to make the sensor ...


4

Backscatter (standoff) lidar for fine particulate matter concentrations is very hard, but doable. There is a company in France that offers it (LEOSPHERE), but their website is down. I found that through this paper. There are also people that do this or attempt to do this for roadside emissions sensing. Both of these systems use ND-YAG lasers that are ...


4

Any general-purpose NPN transistor will work in that application. 2N4401, 2N3904, 2N2222, etc.


4

In answer to part 1 of your question: Argon is readily available (check welding supply centers) and has about 1/5 the dielectric strength of air. Helium, also fairly available, has about 1/6.5 the dielectric strength of air. In answer to part 2 of your question: Yes, reduced pressures generally reduce the dielectric strength of gasses. (note: Lower ...


4

The sensitivity in the data sheet says that, for 1 PPM change in the gas concentration, there will be approximately 55 to 90 nA of current change. It is always relative and hence, initial calibration is very important. We are using several other gas sensors from the same vendor.


4

I guess it's derived from the American term for vehicle fuel being referred to as gas. Many countries refer to it as fuel or petrol. The Wikipedia article Fuel gauge starts off with the following: A fuel gauge (or gas gauge) is an instrument used to indicate the level of fuel contained in a tank So I guess from that point of view it makes sense, when a ...


3

You are absolutely right, this sensor gives you a single output, and you don't get any hint if for example Rs/R0 = 0.9 is caused by 200ppm CH4 or 1000ppm H2. If Rs/R0 < 1, you may say that the gas is CH4, but not CO: CO will never cause such small values within the measurement range of the sensor. But you don't know what happens for very high ...


3

As Jacob said you can use LD33V to convert voltage to 3.3v but you can also use optocouplers like PC817 to couple or isolate your circuit.


3

From the MQ-135 Datasheet you can see that the sensing resistance is 2 kΩ to 20 kΩ and the test circuit shown is really just forming a voltage divider from the 5 V supply with the lower end being RL. If you select RL as 3.3 kΩ when the sensor resistance is 2 kΩ the output will be 3.113 V and when it is 20 kΩ it will be 708 mV which you can directly connect ...


2

I'm not 100% sure if this is the right site for this, since this has nothing to do with electronic design. But hey, it's fun to take on some math problems once and then. Let's ask ourselves this: How much total heating capacity is required for one whole hour? For every kWh we need 14.5 MJ, how many kWh is there in 300 MWh? Number of kWh in 300 MWh is = \$...


2

For a 300 MW power plant, 14.5 MJ/kWh of heating capacity must be provided. 1 kWh = 3600 kWs = 3600 kJ = 3.6 MJ (since there are 3,600 s/h). If your power plant is 100% efficient then it would require 3.6 MJ of heat to produce 1 kWh of electricity. If your power plant is 40% efficient it will require \$ \frac {3.6}{0.40} = 9 \ \mathrm {MJ/kWh} \$. That is,...


2

1 kWh is 1 kW (power) for 1 hour, 1 hour is 3600 s, so 1 kWh is 3.6 MJ, but you don't need this as you are not asked to calculate the efficiency (Which is clearly poor). The question is mostly a nasty excersize in units conversion, or in noticing the shortcuts. For example you need 14.5 MJ per kWh of electrical output, so at 300 MW electrical, you need 300,...


1

I have used the MQ-6 extensively. It takes minutes to warm up to get a stable reading. My experience is that if you stay within the voltage specifications for this device it will last 2-3 years before it burns out. If you only need a reading every hour the approach of powering it up for a few minutes and taking a reading will make it last much longer.


1

Gases have extremely low electrical conductivity, all of them. This is because they are basically a vacuum with "a few" electrically neutral molecules in it. When you ionize such molecules by some mean (e.g. increasing the temperature) you obtain what is called a plasma, which you can imagine as gas made by ions and electrons. In particular, if you have a ...


1

The transistor is being used as a switch so you should be able to use almost anything provided it can handle the current - not that a 1/2W speaker needs much current. As for the lack of sound, are you using a speaker or a buzzer, if your using a speaker, the frequency driving it may be too low, if you can see the led pulsing, it's got to be below 50Hz, not ...


1

Look for gas flow meters, there are ready made solutions on the market. You do not want to mess with combustible materials, sparks (from your electronics) can blow your coffee shop to the sky.


1

What you are looking for is a transformer with a 117 volt primary, 3.3 volt secondary, and at least 4 amp current. You can't get this, exactly, but a standard 220 / 6.3 volt transformer connected to 120 VAC will give you a nominal 3.15 volts, which should be close enough.


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