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Flatulence is a common problem that arouse in the near past especially in the older aged people. Basically human faeces are sterile and odourless. But, it may acquire a foul odour due to some bacterial actions. Sometimes these emit gases which are odourless yet harmful. The nature of the gases emitted from a human body during flatulence varies according to the kind of diet that the person has taken and of course the nature of the body. From a literature survey conducted on incontinence sensors it was found that the current existing methods such as Peritron Perineometer, MEP etc. are mainly invasive involving the study of muscle movements etc. So, a need for an incontinence sensor is essential which is non-invasive and which can detect harmful gases emitted to see the presence of an abnormality. But the current objective of this report includes the identification of one of the gases emitted, methane, the dependency of methane with oxygen and its variation according to the height of the sensor. The dependency of methane with oxygen will aid in finding out false negatives with reference to methane:oxygen ratios and the height of the sensor would help in determining the position that the sensor needs to be placed in order to get a correct reading.
The aim of the project is in relation to the measurement of the amount of combustible gas, in this case methane, from an environment. This measurement is principally done with the aid of multiple instruments like Vernier LabQuest, TPI-725 etc. As the main context of this experiment is related to human body, an attempt is also made to find an ideal position where the sensor needs to be placed and also to identify if the amount of methane measured varies with height. The above said instruments use entirely different principles to identify the amount of gases including the combustible ones. The main principles being used for oxygen and methane include electrochemical cells, semiconductors and optical sensors. A brief description on the principles and the materials being used in the sensors are described in the later section of the report.
The aim of the experiment is in context with incontinence sensors. Incontinence can be defined as the inability to control the bodily evacuative functions in relation to urination etc. Incontinence is basically not a disease but can be defined as the abnormal function of one or more body parts or systems. The existing methods involved in these sensors are invasive and hence it becomes uncomfortable for the subject or the patient to cope up with the instrument. So, evidently there is a need of a handheld small device that will be capable of measuring the amount of gas released. A gas detector is basically a device which can detect different gases in an environment depending upon the sensors used. It may give out a reading of the amount of the gas present and also sound an alarm if the amount of gas goes beyond a threshold. And since the detectors measure the concentration of a gas, it responds to a calibration gas which acts as a reference. Gas detectors can be classified mainly as combustible and toxic gas sensors based on the type of the gases they detect. They can be further divided on the basis of the technology being used. For example, catalytic and infrared sensors are used to detect combustible gases and electrochemical and metal oxide semiconductor technologies are used generally for detecting toxic gases.
The wide range of gas sensor technologies currently in use are:-
Catalytic bead sensor
Infrared point sensor
Infrared open path detector
Flame ionization detector
Nondispersive infrared sensor
Zirconium Oxide sensor cell
Metal Oxide Semiconductor
Sample Collection and Chemical Analysis
Some of the principles mentioned above are described in the later part of the report. The position of such a sensor in the body also plays a very important role. There should be an ideal position where the electrode must be placed in order to measure the right data without any false negatives. The odour creating substance in human urine is mostly amino acids. But there are also substances like skatole, indole, hydrogen-sulphide, ammonia. But our interest lies in the amount of methane measured in a similar situation as there is a wide variety of sensors that are available which can detect the amount of Methane in air. So, the main gases under the scope of this experiment will include Methane and Oxygen. The recording of methane:oxygen ratios is also an area of interest and also to practically find out if the amount of methane would decrease with an increase in height and will that create an increase in the amount of oxygen as the sensor moves up. It has also been identified that Methane is also a really potent gas which can increase the chance of greenhouse effect.
It has a higher global warming potential when compared to Carbon Dioxide by about 20 times, the reason of which is explained by the reaction below.
CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l) + 891 kJ/mol (at standard conditions)
On calculating the molar ratios of the methane and carbon dioxide, it can be concluded that every 1g of Methane in presence of oxygen can produce approximately 2.75g of carbon dioxide.
The manner of usage of the four principal instruments being used for the experiment is mentioned below. The technical specification of every instrument including their data sheet is presented in Appendix A.
The device that was first used to study the amount of gas was Vernier LabQuest. This is a multi-tasking handheld device which has numerous capabilities. Six of the current Vernier sensors can be connected on to the device simultaneously in order to record data. The device itself has a 7cm*5.3cm screen which incorporates a 320*240 pixel colour display which provides a touch screen interface. The device can work both as a standalone product or it can also be connected into a laptop or a PC to perform the same functions. In the scope of this project, only two of the Vernier sensors are used which detects the amount of Oxygen and Carbon Dioxide. On utilising the Vernier Labquest for the measurement of these gases, the readings can be taken in three units which are Percent (%), Parts per Million (ppm) and Parts per Trillion (ppt). It simultaneously takes instantaneous value over a period of time, records it over a table, plots a graph and also provides an option of storing the data recorded in its in-built memory. The drawback of this instrument however is that this device does not have a sensor that can be attached in order to detect the presence of combustible gases like methane etc.
TPI - 725
TPI - 725 is a small handheld device that was manufactured by Test Products International. It measures the amount of combustible gases in an environment. It basically has an On/Off button and five LED lights on it which basically tells you when the device is ready and how much is the gas intensity of combustible gases principally Methane. This device is powered by two normal 1.5V AAA batteries.
The lights on the instrument denote the amount of combustible gas that is detected. The four lights on the top denote the increase in the amount over a particular level. This is described below:-
LED 1 ïƒ¨ >5,000 ppm
LED 2 ïƒ¨ >4,000 ppm
LED 3 ïƒ¨ >2,000 ppm, and
LED 4 ïƒ¨ >1,000 ppm.
The light at the extreme bottom would denote if the device is switched on and also tells you when it is ready to be used and when the battery is low. This device however has several advantages and several disadvantages. Firstly when looked into the advantageous points, we can see that it is a completely portable handheld device that can be attached anywhere on the body which can tell you exactly as to what is the level of Methane in the current environment. There is also no necessity to recalibrate the instrument each and every time before a reading is taken. However, the drawbacks that this instrument has are that it would not be able to tell you the exact concentration of methane in ppm especially for the experiment under progress. As mentioned earlier, the instrument would try to reset its auto-zero when switched on but a problem may arise if the device does not find the auto zero and never goes ready to take readings.
Kane May CD100A is a handheld instrument which measures combustible gases some of which are acetone, alcohol, ammonia, benzene, methane, butane etc. It basically contains a 40cm gooseneck with a tip light which detects the area of the leak and also it has a ticking alarm by which the tick-rate increases with increase in the concentration of combustible gas. The frequency of the flashes also increases with an increase in the concentration of the gas. The long gooseneck also helps in identifying areas of leak in difficult to reach areas in both residential and commercial applications. The instrument contains a low-power semiconductor sensor which burns on exposure to combustible gases or vapours.
When the instrument is initially switched on, a constant tic rate is adjusted using the rotating thumbwheel in fresh air. This is set as the background. Then the instrument is brought into the areas of suspected leakage. The frequency of the flashing lights and the tic rate increases when there is an increase in the amount of methane equal to or over 50 ppm. Then the thumbwheel is again rotated back to a steady tic rate which resets the background for the instrument and the gooseneck is moved further inside to detect more amount of leakage. The only drawback of this instrument in context to this experiment is that it only provides a tic sound and a flashing LED light saying that the amount of combustible gas has increased but does not tell us by how much has it increased or what amount of combustible gas is there in a particular environment.
Quantum GasPod is basically a handheld instrument that could be just hanged over the neck or attached to the pocket with a clip. It measures the amount of oxygen in air continuously. It provides dual protection for the user by providing protection from oxygen deficiency in the presence of nitrogen, argon and helium together with monitoring of oxygen enrichment in percentage (%). This device is comparatively of less use to this experiment as it provides a continuous reading only as percentage. It is much preferred to use Vernier LabQuest for this purpose as it shows oxygen concentration in percentage, ppm and ppt even if it is a bit more bulky when compared to Quantum GasPod.
STATE OF THE ART SENSORS
The continuous real-time measurement of oxygen is extremely important in day-to-day life as well as in a hospital. Oxygen sensors also play a very important role in clinical applications especially during intensive care situations when the patient has to be under anaesthesia. The sensors that is used should ideally have the following characteristics which are it should be highly sensitive, capable of continuous measurement, should be portable (in most of the cases from an application point of view) and should be able to denote the amount of Oxygen in multiple units like %, ppm or even ppt. There are several kinds of sensors that are being used currently in the market which includes electrochemical and optical sensors etc. with different substances as sensing elements. Some of the principal oxygen sensors are discussed below.
Electrochemical sensors are now the most widely accepted methods of finding the amount of oxygen in an atmosphere. The measurement was initially done with the help of zirconia (zirconia.pdf) doped with metal oxides like yttria or calcia at temperature approximately 700-870 degrees. A transition metal oxide reference sealed to zirconia can also be used so that it generates a thermodynamic reference oxygen level. The metal/metal oxides that were chosen were palladium and nickel as they gave more close signals with respect to the thermodynamic predictions. The probe was then sealed by an alumina-silicate glaze material as it could contain the expansion properties of zirconia and alumina.
Since the calibration and the use of such a sensor were a bit difficult in day to day life, there was a new form of electrochemical sensor that came into effect. This new sensor (electrochemical o2 sensor) had no covering membrane over the sensing electrode. The sensor was fabricated from a smooth glassy carbon material.
Block diagram of Oxygen Sensor
The electrochemical sensor or cell basically consists of three electrodes, the smooth glassy carbon working electrode, sand-blasted platinum counter electrode and a silver/silver chloride reference electrode. The second part includes a voltage source and a trigger circuit followed by a potentiostat and a time-controlled integrator.
Two different potentials say -1V vs. Ag/AgCl as measuring potential for 10-50ms and 0V vs. Ag/AgCl as resting potential for 0.5-100s is set at voltage source and applied at the carbon electrode through the potentiostat. The oxygen gets reduced only when the working electrode remains at the measuring potential where it triggers a TTL pulse and delivers it to the integrator with a time lag. This time lag resets the integrator and also ensures that there is no capacitive current involved. By varying the amount of gases in the mixture being analysed, the sensor could rapidly detect the change in the amount of oxygen in the electrolyte under consideration and it gives a constant value in less than 2 minutes. This electrode can be utilised both for industrial purposes as well for implantation etc. due to its biocompatibility electrode material and low energy consumption. So, to conclude on this electrochemical sensor, the principal advantages of this sensor would be very short response time, absence of the membrane, low energy consumption and low oxygen consumption.
Resistive Oxygen Sensors
Resistive Oxygen sensors have gained much importance due to their compactness and simple structure when compared to the traditional electrochemical cells. There are currently numerous resistive sensors based on CeO2, TiO2 , Ga2, O3, BaTiO3, (Nb), TiO2(Nb, Cr), and SrTiO3 (resistive o2 gas sensors). But the main disadvantage of the semiconductor oxide resistive oxygen sensors were that the response time was high and the sensors where sensitive to temperatures. This may cause variation in the physical properties of the sensor like variation of free carrier concentration, the energy gap, Fermi Energy etc.
The semiconductors are basically of two types which are n-type and p-type. Generally, the electrical conductivity of an n-type semiconductor would be:-
σe = qμene
where μe is the electron mobility, q is the electron charge and ne is the electron concentration. But what should be noted is that both μe and ne is temperature dependant. So , μe can be defined as
μe = μ0 T-m
Where T is temperature and m is it power exponent. The value of m is usually equal to 1.5 at high temperature for crystalline semiconductors and may rise considerably for disordered semiconductors. So, as we can see there is a clear dependency between the conductivity and temperature. On evaluating the concentration of electrons n as a function of temperature and oxygen pressure it can be seen that n will be represented by the equation:-
Where Ef = Ef,o - (kT/2(γ+1)) Ln (Po2/Po2,0) and Eg(T) = Eg(0) - (αT2 / β+T)
So, on substituting the equations, we get:-
Similarly, for a p-type semiconductor σh is given by the following equation:-
So from the above equations it has been clear that both for n-type and p-type semiconductors, the conductivity would depend upon both the operating temperature and oxygen gas pressure. So considering the following principle an n-type semiconductor was chosen (Cerium oxide) and a p-type semiconductor was chosen based on SrTi0.65Fe0.35O3−δ. On considering the temperature range and constant oxygen gas pressure 1Pa, both these sensors were testes to find the sensitivity and compare it with the theoretical values. It could be seen that the p-type SrTi0.65Fe0.35O3−δ sensor only varies by approx. 1% from the theoretical values. It was also seen that it behaved as n-type semiconductor at low oxygen pressures and behaved as a p-type semiconductor in high oxygen pressures. And considering the n-type semiconductor which is CeO2, three grain sizes were used at a temperature of 800-1250K at an oxygen pressure of 105 Pa. The results that were obtained was compared again with the equation above for n-type semiconductors and when graphs were plotted there was found to be a mismatch of only 0.8%.
But the main disadvantage of semiconductor oxide resistive sensors was still there which it was taken more time to respond to any changes in the amount of gas detected. So, several experiments were carried out by Beie and Gno¨rich (references.doc) on how to reduce this drawback. They conducted several experiments on thin and thick CeO2 films (Thick Ti sensors.pdf). They were prepared initially using Cerium oxide thin film powder (ceo2 fine powder). An average thickness of 200nm and 2000nm was made through mist pyrolysis for the purpose of the experiment. The response time of the sensor can be defined as the time when the ratio (σ-σ1.0)/(σ0.010-σ1.0) becomes 0.9 after the change in the pressure of oxygen. In the equation, σ1.0 and σ0.010 represents stable electrical conductivity in and oxygen pressures of 105 and 103 Pa.
It was observed that the response time of the sensor was about 10s when the oxygen pressure was changed for a particle size of 200nm which was approximately 1/10th the response time when the experiment was carried out with a larger particle size of 2000nm. The graph below shows the variation of response time with a change in the gas pressure of oxygen. And seen from the graph it can be clearly observed that the response time has evidently gone with a decrease in the size of the particle.
Variation of response time using thin CeO2 films for a pressure change from 105 to 103 Pa at 985K (ceo2 fine powder)
Several experiments were done on Cerium Oxide powder as it played a definite part in the measurement of oxygen. Due to its high dependency on partial pressure of oxygen and temperature, Cerium Oxide is doped with different to design an oxygen partial pressure measurement material (OMM) and a temperature compensating material (TCM). So, the first notable change in the material of TCM was the use of Ce0.9Y0.1O2−δ which is basically a yttrium-doped cerium oxide. The results were then compared to a non-doped Cerium oxide sensor.
The principle of designing an OMM and a TCM is described below. The resistance of OMM, defined as ro and resistance of TCM, defined as rt can be defined by the following equations:-
Where Eo and Et are the activation energy of OMM and TCM resistance. On applying a potential difference with a constant voltage V, output voltage Vout can be defined by the equation:-
On considering Eo is equal to Et it can be derived that, Vout would be equal to:-
So, it can be seen that when Eo is equal to Et, the temperature dependency nullifies (tcm2004.pdf). So, on reducing the difference between Eo and Et, the temperature dependency can be reduced. The experimental setup for the experiment is shown by the figure below:-
And as the result of the experiment conducted, Ce0.9Y0.1O2−δ was found to have very small dependence on partial oxygen pressure but same characteristics as that of a non-doped Cerium oxide. But, on further research cerium was then doped with solid electrolyte Zirconia. As the result of the experiment conducted, it was concluded that Ce0.95Zr0.05O2 thick films could be used for OMM and Zr0.70Y0.30O2−δ thick films as TCM (tcm.pdf). The output of the sensors however were approximately temperature independent at high oxygen partial pressure range but a very small temperature dependency at low partial pressure range. Later experiments were carried out by doping ceria oxide (cerium oxygen sensor.pdf) with hafnia instead of zirconia as hafnia doped ceria had a lower resistance and a lower temperature dependence of resistance than the zirconia doped ceria. So, different mol% of hafnia was doped on ceria to see the differences (hafnia). Activation energy was measured as a decrease in activation energy means decrease in temperature dependence on resistance. The activation energy in a high temperature region over 7 mol% was similar to that of 0 mol%. But, the hafnia-ceria system showed more excellent properties between 7-20 mol% than the non-doped ceria with respect to low resistance, good sensitivity, and small temperature dependence of resistance.
The principal type of sensors used in the detection of methane is basically involves semiconductors and noble metals as catalysts. The noble metal catalysts include ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold. The most common materials that were used for methane sensors were ZnO (electrochemical ZnO sensor) and SnO2. But SnO2 was widely used as SnO2 thick films had high sensitivity to detect hydrocarbons. This is because the noble metal catalyses the reaction between methane and adsorbed oxygen leaving conduction electrons or vacancies in oxygen behind. Thin films using nano-crystalline ZnO sensors made through sol-gel methods was also found to be an ideal material for methane sensing (nanocrystalline ZnO.pdf). Based on this principle, there were several modifications that were made to these sensors. Some of the research done in this respect is described below.
Selectivity and Specificity (selectivity.pdf)
The selectivity of the desired gases indeed depends on the noble metal catalysts that were chosen for the sensor. The grain size and dispersion of the noble metal catalyst, grain size of SnO2 and on the oxides on the surface determines the long term stability of the sensor. From experiments that were conducted, it was found that large grain sized SnO2, Al2O3 and Pd should be compounded to the SnO2 to increase the sensitivity. Selectivity can be attained through the deposition of thick layers and also by applying filters. The long-term stability can be imposed by annealing it at high temperature.
Noble Metal Catalysts over Tin-oxide (sdarticle.pdf)
It has been found that when tin-oxide sensors are loaded with noble metals, it is rather difficult and to control metal dispersion. So, based on that conclusion, the tin oxide powder was mixed with alumina (or silica) supported noble metal catalysts. The SnO2 was coated with a lot of additives and supported metal catalysts.
So, it was observed from the graph that the lowest sensitivity is for pure tin oxide (1). But, it can be noted that the sensitivity with respect to methane concentration was found to when 0.1 weight% of Calcium (2) and Platinum (3) were added. Then, 5 weight% of alumina supported with Pt catalyst was tried and it gave a sensitivity as shown in the graph (4). It was also then tried with 5 weight% of alumina with Pd catalyst which had more sensitivity which was again found to increase as shown in (6) in the graph when SnO2 is having Ca and Pt as additives in 0.1 weight%. And it was found that the sensitivity of methane was found to increase in the order Pd/alumina ïƒ¨ Rh/alumina ïƒ¨ Pt/alumina ïƒ¨ Ni/silica ïƒ¨ non-coated tin oxide. This was because the Pd oxide particles have better high dispersion on the surface with the alumina as a catalyst when compared to the others when coated on tin oxide. And it was also observed that with an increase in the concentration of Pd/Alumina from 0-5 weight% created a significant change in the amount of sensitivity but did not make much of a difference when it was increased to 10% of SNO2. So, it was hence concluded that SnO2 (Ca, Pt) with Pd/Alumina is the better combination of materials that can be utilised in order to measure the amount of methane. But this sensor had a drawback as it was non-selective in detecting methane as it provided higher sensitivities for propane and butane.
Osmium - SnO2 sensors (osmium.pdf)
Osmium doped SnO2 sensors were fabricated for the purpose of identification of methane at a lower temperature. This is because methane is thermodynamically more stable when compared to other reducing gases and hence comparatively difficult to detect it with high sensitivity below 350-400oC. So, osmium was doped on to tin oxide by sol-gel technique and experiments and test were carried out. It was then observed that osmium doped tin oxide sensors increases the sensitivity of methane and also provides much higher sensitivity at a much lower temperature. But the only disadvantage of this method was that it could produce cross-sensitivity effect for example with carbon monoxide. But, this could be eliminated by using the sensors in an array configuration.
Iron-doped SnO2 sensors (methane and butane.pdf)
The purpose for which the SnO2 sensors were doped with iron was to identify if the sensor mentioned above could detect methane and butane separately. The manner in which this was carried out was through modulation of temperature. So, SnO2 powders with 0-0.5 weight% of Fe2O3 were prepared in the presence of 0-2 weight% of Pd catalyst considering the sensitivity properties. But it was found that the curves for 1000ppm methane and butane gave response peaks at 350oC and 425oC. However they plotted a peak in the range of 350oC when Pd is added on to it.
Optics based portable Methane Sensors (optical.pdf)
Most of the sensors described above are not methane-specific as any of the combustible gases that burn the detector will be detected. So, there are chances of poisoning the detector giving rise to false readings. So, it is essential to develop an optical sensor based on semiconductor source in order to sort this problem as it has potential advantages as described below
Ability to detect specific gases by choosing particular wavelengths,
Ability to work in a zero-oxygen environment,
Low cost of ownership and lack of poisoning.
Several methods have been done to make a low cost methane sensor both in normal and in aqueous environments (low cost.pdf) which would not compromise on reaction times, temperature and coefficients. The strongest optical absorption takes place in the mid-IR region at about 3.3µm. But the main disadvantage of it is that in that range, there are chances that several other hydrocarbons will be detected and also mid-IR detectors are quite expensive. So, a wavelength of approximately 1665nm which is the near-IR region as there are inexpensive LEDs and detectors in the market which operate with very less noise at room temperature. However, the magnitude of the signal fed into the detector would be weaker than when a mid-IR detector and source is used. Different configurations of source detector arrangements were tried out and they are described below.
The first configuration used included an active and a reference LED source of different wavelengths. This had issues as different LED sources have different temperature coefficients which can lead to false detection of signals. One of the solutions found to this problem was that to employ a second detector placed next to the source LEDs. This acts as a feedback and maintains same intensity is maintained at the output of both LEDs. However this arrangement is practically difficult to achieve and it is expensive too. So, a third arrangement was made were source and the detector was placed at the same end and by placing a mirror at the opposite end thereby increasing the path length. The same process was carried out by placing a lens with the photodiode. It was found that the absorption of methane increased with an increase in the path length. It was also observed that the absorption also increase with the lens being added on to the setup because in the presence of the lens, it accepts the light that has travelled directly through the cell and back again whereas without the lens, it acquires backscattered lights which do not have much path length. And in the final arrangement, the two detectors are used of the same model number to cancel out the effect of temperature. The active filter absorbs in the region of methane absorption lines and reference filters outside the methane absorption lines. But it was made sure that the wavelengths chosen for the reference filter was closest to that of the active filter and with a sufficiently narrow bandwidth. For methane-specific sensors, it should also be made sure wavelengths are chosen in such a manner that it should lie outside the absorption lines of other hydrocarbon gases. And to achieve temperature stability, both the detectors were placed in a single aluminium block to ensure same temperature and hence thermal mass of the detectors.
Several other sensors were designed which could detect oxygen and methane simultaneously (CH4 sensor and method.pdf) using SnO2 or a doped form of SnO2 at higher temperatures for methane gas detection and an oxygen sensitive semiconducting metal oxide for oxygen sensing. The types of semiconducting materials that can be used for oxygen sensors discussed in the state of the art sensors for oxygen described in the previous section of the report.
The basic experimental setup used for the experiment is described below. Two metallic clamps are attached to a vertical stand. One of them is kept fixed for the purpose of keeping the sample. Samples are held in a plastic cylindrical container. The solvent under consideration for this experiment is a serious decision to make. The most preferable liquid however was found to be acetone. The other solvents that I tried to employ were methanol or ethanol. But, the main drawback of the solvents were that both methanol and ethanol are not so volatile and hence may not go into the gaseous state and may lead to a chance that the detector cannot detect it. There are five plastic containers being used to identify the effect of concentration. The detector device is kept on the moving metallic clamp which is moved by 10cm upwards from the sample to see if there is any variation in the amount of gas measured with respect to height of the device from the sample.
The device used for the measurement of oxygen and carbon dioxide is the Vernier LabQuest and the amount of Methane is detected by Kane May CD100A. A limited attempt to use TPI 725 is also done to detect the amount of methane present. Quantum Gaspod was utilised to continuously measure the percentage of oxygen in air. This device is described less when compared to others as it is comparatively irrelevant with respect to other devices employed.
The experiment was done as described by the setup mentioned above. The observations that were made are described in this section. On the basis of readings given by Vernier Labquest for oxygen and tic rate give by Kane-May CD100A the following tables and graphs were plotted. But there were several assumptions that were made while plotting the graph. The graph shows the trend of oxygen and methane variations but does not show the exact values on the y-axis as the scale for methane and oxygen are different. Assumptions were also made for the tic rate correspondence to the ppm as follows:-Normal ïƒ¨ 200ppm, Almost Normal ïƒ¨ 300ppm, Very slight increase/Notable increase in tic rate ïƒ¨ 450-500 ppm and Steady increase in tic rate ïƒ¨ 600-850ppm.
5ml Acetone readings
Oxygen (in ppm)
Methane (on the basis of tic rate)
5ml acetone vs 20ml water readings
Noteable increase in the rate
The readings shown above are for the most diluted solution of acetone which contains 5ml acetone and 20ml of water. It can be seen from the graph below that the trend for methane is almost constant which slightly rises as the distance is increased and the level of oxygen decreases rapidly during the slight rise in the amount of methane.
10ml Acetone readings
Oxygen (in ppm)
Methane (on the basis of tic rate)
10ml acetone vs 15ml water readings
Very slight increase
Increase in the tic rate
With the 10ml of acetone mixture with 15ml of water, the trend observed is shown above. But, as seen from the above graph it can be seen that the level of oxygen still decreases after a distance of 5cm whereas the methane trend remains almost constant which basically
means that the methane concentration increases after a distance of 20cm with respect to oxygen. So, on the basis of readings so far the ideal distance for methane sensing can be predicted as 20cm.
15ml Acetone readings
Oxygen (in ppm)
Methane (on the basis of tic rate)
15ml acetone vs 10ml water readings
Very slight increase
Increase in the tic rate
The graph shown above which contains 15ml of acetone and 10ml of water is quite similar to the graph obtained for 10ml of acetone to 15ml of water. However the only difference that was found was that after 20cm, the level of methane was seen to increase rapidly with respect to the oxygen level and when compared to 10ml acetone solution.
So, again the possible ideal position for the placement of the sensor could be somewhere between 20 and 10cm to sense the increase in methane gas.
20ml Acetone readings
Oxygen (in ppm)
Methane (on the basis of tic rate)
20ml acetone vs 5ml water readings
Very slight increase
Very slight increase
Noteable increase in the tic rate
On using 20ml of acetone with 5ml of water, a similar observation was made although the graph showed a sharp increase at 20cm and then came down when the distance was reduced to 10cm. So again, on considering a small error margin at 20cm it was observed that the methane gas could be sensed ideally somewhere between 20 and 10cm.
25ml Acetone readings
Oxygen (in ppm)
Methane (on the basis of tic rate)
25ml acetone vs 0ml water readings
Very slight increase
Tic rate increases gradually
Steady increase in tic rate
When a pure concentrated 25ml of acetone was employed, it was seen that the trend of methane gas was seen to increase steadily and also at a constant rate with respect to oxygen after a distance of 20cm. It can also be observed that the rate of increase in the amount of methane measured increases at a faster rate for a fully concentrated 25ml of acetone.
The other two instruments, Quantum GasPod and TPI-725 were utilised to a limited extent for this project. The data provided by Quantum GasPod was comparatively irrelevant as it only denoted the oxygen amount in percentage and always gave a constant reading of 20-20.5% always which was significantly high when compared to the readings from the Vernier instrument in ppm. Also TPI-725 was quite sensitive to high methane concentrations and there was a risk of damaging the sensor of the instrument when exposed to high concentrations of acetone. So, this was only used for larger distances ranging from 40cm to 20cm. For a distance of up to 20 cm, there was no indication of methane above 1000ppm by TPI-725.