Measuring the Depth of Water Using Sound Waves

Measuring the Depth of Water Using Sound Waves
Aim The aim of my investigation was to create a sensor which could measure the depth of water in a tank. Plan The way I proposed to measure the depth of water was using sound waves which would be emitted and fired into the tank of water. The sound wave should then be reflected of the bottom of the tank and picked up by a microphone. The microphone would be linked to an oscilloscope and the sound emitter would be linked to the oscilloscope. I would then measure the phase difference between the waves. Then by changing the depth of water in the tank, I would see what relationship would be produced between the phase difference and water depth and test how well the sensor worked. Below is a circuit diagram which shows how I wanted to lay out my investigation and the components involved: The safety conditions I took into consideration when I did my investigation were where:
Be careful with all electrical equipment.
Never touch electrical items with wet hands.
If an accident occurs warn teacher immediately.
Keep all items e.g. backpack out of peoples walking path.
Always listen to what the teacher is saying.
Keep round items and glassware which can roll firmly on the table.
Method The method of my investigation was as follows: 1) I firstly set up the experiment as the diagram below shows: 2) I then used the loudspeaker which was connected to a signal generator to produce a sound wave directly into the tank of water. 3) The reflected wave was then picked up by the microphone. 4) The loudspeaker was connected to one input of a cro (cathode-ray oscilloscope) and the microphone to the other. This allowed the original sound wave from the loudspeaker and the reflected sound wave picked up from the microphone to be shown on the oscilloscope screen. 5) I then calibrated the time base on the cro so that both waves could be easily compared and so that they looked similar to this: 6) Then by measuring the phase difference by using the displacement X a relationship between the depth of water and phase difference could be formed. Record of Observations During the course of investigation many things happened to which I responded differently. When I started of the experiment I was in a large room with many students and had the following equipment: sound box generator, oscilloscope, loudspeaker and a magnetic microphone. The first problem I found was that the magnetic microphone I was using was not sensitive enough to pick the reflected sound wave. At first I thought I would solve this by using a sound amplifier so that the sound wave would be strong enough to be picked up but this would have only lead to more noise being introduced into the wave. I finally came to the conclusion that best idea would be to use a more sensitive microphone so I replaced the magnetic microphone with a crystal microphone. I straight away saw a difference as the reflected sound wave was being picked though this did increase the amount of noise that was also picked up. The other problem I found was that there much noise being picked by the microphone from the background and from the students. This disallowed me to take any proper accurate measurements of the phase difference. I tried to solve this at first at first by earthling the microphone and even though this reduced the some of the noise there was still enough so that I still couldn?t take any accurate readings. The only way I could solve this was by moving to a room were there was not a lot of background noise for the microphone to pick up. So I moved to a small room where I was working alone. This caused a drastic decrease in the amount of noise that was picked up by the microphone and allowed me to take much more accurate readings. Now that I could actually take accurate readings I started to coordinate the equipment so that I could produce better results. The wave format I used was the Sine wave as it was the easiest format for me to measure my readings with. What I found was that any frequency levels below x100 didn?t produce a reflected wave even when the time base control was changed. The best shape produced by these frequencies was only a flat line which was useless. At x100 frequency I was able to produce a reflected wave that I was able to make accurate readings with. The settings I used were: Frequency: 5Hz Range: x100 Wave format: Sine Time base control: 5ms/Div When I tested my results I decided to test my sensor with only a certain range of depths and the range I used were 55mm to 35mm. I repeated the readings three times for the above setting to ensure that my results were reliable and made an average for them. The above settings produced the following table of results: Depth of water(mm) 1st Wave length(cm) 2nd wave length(cm) Phase Diffrence (x) (cm) No. of repeats 1 2 3 1 2 3 1 2 3 Average 55 1.3 1.0 1.3 1.8 1.5 1.8 0.5 0.5 0.5 0.5 54 1.3 1.0 1.3 1.8 1.5 1.8 0.5 0.5 0.5 0.5 53 1.3 1.0 1.3 1.8 1.6 1.8 0.5 0.6 0.5 0.5 52 1.3 1.0 1.3 1.8 1.5 1.8 0.5 0.5 0.5 0.5 51 1.3 1.0 1.3 1.8 1.5 1.9 0.5 0.5 0.6 0.5 50 1.3 1.0 1.3 1.9 1.5 2.0 0.6 0.5 0.7 0.6 49 1.3 1.0 1.3 2.0 1.6 2.0 0.7 0.6 0.7 0.7 48 1.3 1.0 1.3 2.0 1.6 2.0 0.7 0.6 0.7 0.7 47 1.3 1.0 1.3 2.0 1.6 2.0 0.7 0.6 0.7 0.7 46 1.3 1.0 1.3 2.0 1.6 2.0 0.7 0.6 0.7 0.7 45 1.3 1.0 1.3 2.0 1.6 2.0 0.7 0.6 0.7 0.7 44 1.3 1.0 1.3 2.1 1.7 2.1 0.8 0.7 0.8 0.8 43 1.3 1.0 1.3 2.1 1.7 2.1 0.8 0.7 0.8 0.8 42 1.3 1.0 1.3 2.1 1.7 2.1 0.8 0.7 0.8 0.8 41 1.3 1.0 1.3 2.1 1.7 2.1 0.8 0.7 0.8 0.8 40 1.3 1.0 1.3 2.2 1.8 2.2 0.9 0.8 0.9 0.9 39 1.3 1.0 1.3 2.2 1.8 2.2 0.9 0.8 0.9 0.9 38 1.3 1.0 1.3 2.2 1.8 2.2 0.9 0.8 0.9 0.9 37 1.3 1.0 1.3 2.2 1.8 2.2 0.9 0.8 0.9 0.9 36 1.3 1.0 1.3 2.2 1.8 2.2 0.9 0.8 0.9 0.9 35 1.3 1.0 1.3 2.3 1.8 2.2 1.0 0.8 0.9 0.9 The above table were all put to 1 decimal place. Then using the above results table I created a hand drawn scatter graph which is shown on the following page. The reason I did this was because it would allow me to see the patterns in my results more clearly and identify any anomalies easily. The scatter graph showed me that the results had a negative correlation. It also showed that even though that I had results which were spread out from my line of best fit they still were not spread out that largely to be anomalous. My scatter graph and results both showed me that the general pattern in my results were that my sensor did measure the change in depth water. They showed me that as the depth increased the phase difference between the waves decreased. This is shown as when the depth was 36mm the phase difference was 0.9cm while at 52mm the phase difference was 0.5cm. It showed that my sensor was working as the change in depth was changing the amount of phase difference. This pattern continued through out the whole course of my results. Now that I knew that my sensor worked at these settings I started to test how good my sensor was at these settings by testing the following qualities: Resolution Sensitivity Response time Small Random Error Small Systematic Error Linear Safe Ergonomics Resolution At these settings the resolution I could tell straight away was low the as it could don?t detect any small changes at all. This is proven as at the depth of water of 55mm to 51mm the phase difference was still 0.5cm and hadn?t changed at all. At these settings the resolution was 5mm as it was every 5mm roughly that the phase difference value would actually change. Sensitivity At these settings the sensitivity was very poor as the changes in the depth of water had to be large in order for the phase difference value to actually change. This is shown as at 43mm to 41mm the phase difference value was still the same at 0.8cm. The reason this would have occurred is because wavelength was large as at x100 and so less sensitive. The low frequency would also be weak in energy and a large wavelength would not need such a high time base control so there would be less sensitive results. Response time The response time at these settings was good as when the depth changed at its resolution the phase difference value would change immediately in a matter of seconds. Also I could see this as when waves were created in the surface of the water the wave would also change corresponding to it as the amplitude would decrease and increase. Small Random Error Through my many repeats I was able to tell that there were no random errors as all my repeated values were close to each other or of the same value. My scatter graph would have also shown if there were any anomalous results and they showed that there were none. The variation in my repeats though may have occurred as it was difficult to pin point the exact midpoint of the sine wave. This may have led to the different values resulting in different phase differences. Small Systematic Error There were a few unpredictable small sounds which did have some effect on my wave format, though as long as I waited for the noise to pass there would not be an effect on my results. What I did find though was that I had taken the repeat reading 3 in a much warmer condition then the repeats 1and 2 and this may been the result of the repeat readings being slightly more different as sound waves travel faster in damper conditions. I made sure the height of the loudspeaker and microphone was at the same height for all the repeats I did. I also made sure the ruler I was using to measure the depth was at the same point for all the repeats. When I was in the room there was a minimum amount of noise interference so my results were very accurate. With the microphone being earthed there was a minimum amount of noise. What I did find was that at these settings any background noise did disturb my results greatly. Linear Though my results had a correlation they were not linear as when the depth was doubled the phase difference did not double. This is show as at 35mm the phase difference was 0.9cm while at 55m the phase difference was already 0.5cm. The depth hadn?t even doubled but the phase difference had already more then doubled showing that my results were not linear. Safe My sensor was safe as all electrical areas were kept well away from the the water to prevent any electrocution. The loudspeaker and microphone were also held firm on the boss and clamp to prevent them falling into the water. Also as a second precaution the top opening gap of the tank was too small for the loudspeaker and microphone to fit in even if they had fallen Ergonomics I would not say that the sensor was built for human use as it would be very tricky for a person who knows nothing about it to use. Maybe if it came with a intrusion manual it would be easier to understand but as it is it would be difficult to understand and work with. Through the testing of my sensor I come to certain ideas and ways of improving the certain aspects of my sensor which where poor. The main poor aspects of my sensor were the resolution and sensitivity and the way I thought of improving this was by increasing the frequency of my sound wave I produce. I got this idea as I saw that there was a poor resolution and sensitivity of my sensor when I used a low frequency of x100 which had a large wavelength. So in theory if I had a sound wave with a higher frequency it would have a smaller wavelength? So, I increased the wavelength to the highest level and found that anything above x1k would not produce a reflected wave with which I could make readings with even when the time base control was put to the lowest. This may have been as the frequency was so high that anything above x1k was out of the crystal microphones range. Though at x1k the results I obtained were easily readable with a time base control of 50us. The wave format I used was the Sine wave as it was the easiest format for me to measure my readings with. The settings I used were: Frequency: 5Hz Range: x1k Wave format: Sine Time base control: 50us/Div I decided to test my sensor with only a certain range of depths and the range again so I used 55mm to 35mm. I repeated the readings three times for the above setting to ensure that my results were reliable and made an average for them. The above settings produced the following table of results: Depth of water(mm) 1st Wave length(cm) 2nd wave length(cm) Phase Difference (x) (cm) No. of repeats 1 2 3 1 2 3 1 2 3 Average 55 1.3 1.3 1.3 1.6 1.5 1.5 0.3 0.2 0.2 0.2 54 1.3 1.3 1.3 1.9 1.9 1.8 0.6 0.6 0.5 0.6 53 1.3 1.3 1.3 2.3 2.3 2.3 1.0 1.0 1.0 1.0 52 1.3 1.3 1.3 2.6 2.7 2.6 1.3 1.4 1.3 1.3 51 1.3 1.3 1.3 2.8 2.9 2.9 1.5 1.6 1.6 1.6 50 1.3 1.3 1.3 3.1 3.1 3.1 1.8 1.8 1.8 1.8 49 1.3 1.3 1.3 3.3 3.3 3.3 2.0 2.0 2.0 2.0 48 1.3 1.3 1.3 3.5 3.5 3.5 2.2 2.2 2.2 2.2 47 1.3 1.3 1.3 3.7 3.7 3.7 2.4 2.4 2.4 2.4 46 1.3 1.3 1.3 3.9 4.0 3.9 2.6 2.7 2.6 2.6 45 1.3 1.3 1.3 4.1 4.2 4.2 2.8 2.9 2.9 2.9 44 1.3 1.3 1.3 4.3 4.3 4.4 3.0 3.0 3.1 3.0 43 1.3 1.3 1.3 4.5 4.5 4.5 3.2 3.2 3.2 3.2 42 1.3 1.3 1.3 4.7 4.7 4.7 3.4 3.4 3.4 3.4 41 1.3 1.3 1.3 4.9 4.9 5.0 3.6 3.6 3.7 3.6 40 1.3 1.3 1.3 5.2 5.2 5.2 3.9 3.9 3.9 3.9 39 1.3 1.3 1.3 5.4 5.4 5.4 4.1 4.1 4.1 4.1 38 1.3 1.3 1.3 5.6 5.6 5.6 4.3 4.3 4.3 4.3 37 1.3 1.3 1.3 5.8 5.9 5.9 4.5 4.6 4.6 4.6 36 1.3 1.3 1.3 6.1 6.1 6.2 4.8 4.8 4.9 4.8 35 1.3 1.3 1.3 6.3 6.3 6.4 5.0 5.0 5.1 5.0 The above table were also put to 1 decimal place. Then again using the above results table I created a hand drawn scatter graph which is shown on the following page. The reason I did this was because it would allow me to see the patterns in my results more clearly and identify any anomalies easily. The scatter graph showed me that the results had a negative correlation as before with the last settings. It also showed that even though that I had results which were spread out from my line of best fit they still were not spread out that largely to be anomalous like my last results. My scatter graph and results both showed me that the general pattern in my results were that my sensor still did measure the change in depth water with the new settings. They showed me that as the depth increased the phase difference between the waves decreased just as before. This is shown as when the depth was 36mm the phase difference was 4.8cm while at 52mm the phase difference was 1.3cm. It showed that my sensor was working as the change in depth was changing that amount of phase difference. This pattern continued through out the whole course of my results. Now that I knew that my sensor worked at these settings I started to test how good my sensor was at these settings again by testing the following qualities again to see if any changes had occurred: Resolution Sensitivity Response time Small Random Error Small Systematic Error Linear Safe Ergonomics Resolution At these settings the resolution I could tell straight away was much higher as it could detect small changes. This is proven as at the depth of water of 55mm the phase difference 0.2cm while just a 1mm decrease to 54mm had caused the phase difference value to change to 0.6cm. At these settings the resolution was 1mm as at it was every 1mm that the phase difference value would change. At these settings it showed my sensor had an incredible resolution as it could detect the change of the depth of water to 1mm. It may have been able to detect an even smaller amount of change in the depth of water but I did not have anything small enough to change the depth of water to that small amount. Sensitivity At these settings the sensitivity was very high as the changes in the depth of water only needed to be small in order for the phase difference value to change. This is shown as at 43mm the phase difference value was 3.2cm and at 42mm the phase difference value had increased by 0.2cm to 3.4cm for a 1mm depth decrease. It showed that the increase in the frequency had resulted in my sensor being much more sensitive to the change in the depth of water. The reason why this occurred is because the frequency was at a much higher value then in the last settings. This resulted in the wavelength of the sound wave being produced being much smaller and having much more energy. This resulted in the results being much more sensitive then the results with the lower frequency as its wavelength was much larger and had less energy. Response time The response time at these settings were the much faster as in the last settings as when the depth changed the phase difference value would change immediately in a matter of seconds. Also I could see this as when waves were created in the surface of the water the wave would also change corresponding to it as the amplitude would decrease and increase and I would have to wait much longer then the last setting for the wave to stop moving. Small Random Error Through my many repeats I was able to tell that there were no random errors as all my repeated values were close to each other or of the same value as they were in my last setting. My scatter graph would have also shown if there were any anomalous results and they showed that there were none. The variation in my repeats though may have occurred as it was difficult to pin point the exact midpoint of the sine wave just like my last settings. This may have led to the different values resulting in different phase differences affecting the overall average of my phase difference. Small Systematic Error Like in my last settings, there were few unpredictable small sounds which did have some effect on my wave format, though as long as I waited for the noise to pass there would not be an effect on my results. All my repeats had been taken in the same conditions so the variations that had occurred must have been for different reasons then from the environment. I made sure the height of the loudspeaker and microphone was at the same height for all the repeats I did. I also made sure the ruler I was using to measure the depth was at the same point for all the repeats. When I was in the room there was a minimum amount of noise interference so my results were very accurate. With the microphone being earthed there was a minimum amount of noise. The major difference I found at these settings that the higher frequency was less disturbed by any noise interference then the lower frequency. If I had whistled at the setting of x100 there would be a large fluctuation in the amplitude of the wave and take above 3 second to return to normal. At the frequency of x1k when I whistled there would a much smaller fluctuation in the amplitude of the wave and would less then 3 seconds for the wave top return to its normal shape. Linear Though my results had a correlation they were not linear as when the depth was doubled the phase difference did not double. This is shown as at 55mm the phase difference was 0.2cm but at 54mm the phase difference had already doubled as the phase difference value produced was 0.6cm. The depth hadn?t even doubled but the phase difference had already more then doubled showing that my results were not linear. Safe My sensor was safe as all electrical areas were kept well away from the water to prevent any electrocution just as in my last settings. The loudspeaker and microphone were also held firm on the boss and clamp to prevent them falling into the water. Also as a second precaution the top opening gap of the tank was too small for the loudspeaker and microphone to fit in. The higher frequency would not have caused my sensor to less safe then compared to the last setting. Ergonomics I would not say that the sensor was built for human use as it would be very tricky for a person who knows nothing about it to use. Maybe if it came with a intrusion manual it would be easier to understand but as it is it would be difficult to understand and work with. The increase in the frequency would make it even more difficult to control as the sensor was much more sensitive at these settings as a slight wave in water would cause the amplitude in the sine wave to move up and down. Conclusion All in all I would say that my basic aim was achieved that I was able to measure the change in the depth of water as my results clearly show that sensor had achieved this. My sensor was one which did the job it intended to do and through testing it I found that its strong points were its resolution, response time, error and safety but it lacked in the ergonomics part. It just wasn?t built for a typical everyday use. If I was to improve any quality of my sensor it would most probably be this. Overall I had produced a sensor which had done what I was intended to do.

Measuring the Depth of Water Using Sound Waves 9.9 of 10 on the basis of 1609 Review.