Water level sensor

In ordinary life, water level sensors are quite widely used. For example: An oil level sensor inside an oil tank, to measure how much oil is left in it because we cannot see it every time, and just find the level on our meters. Also a boiler works on the similar principle, the water in the boiler is quite hot and if we want to see how much the water is, we will be hurt by the vapour. We need the meter for it too. Because water level sensors are very important and there is no alternative for it, I prefer to investigate water level sensors as my coursework.

Planning

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My main equipment is the fixed resistor and uses a float to connect with it using potential divider. While the water level changes, the resistance changes as can be shown on the change of the voltage because the ohm’s law: V=IR. For my circuit, when the resistance changes by the level of water, the voltage changes with direct proportional to resistance. As the water level increased, the Resistance of water level sensor Increase as well. So the voltage share will be change. using R=R1+R2

What is potential divider?

The potential divider circuit is the voltage split up between the components. is split in the ratio proportional to the ratio of the resistance between two resisters. Which mean the voltage share between them, the higher resistance one get great number of voltage (Voltage share = Resistance share) in my circuit there is a fixed resistor which I’m going to explain latter, the resistance can’t change but if the resistance of my water level sensor increase it need more energy to pass through it therefore more voltage is needed. That means the voltage going through my fix resistor is less, because the voltage is fixed. That is how potential divider works.

Circuit

Equipment Needed

A beaker (1000ml), Power supply (6v), Plastic float, Voltmeter, Wires, Automatic rain ganger (different resistor), Measure cylinder, Fixed resistor.

Theory

I am going to choose a fixed resistor for the circuit. It has to be the middle value of the resistor for my water lever sensor. So is work for my potential divider (voltage share = resistance share) because I’m using 1000ml beaker, put the water up to 1000ml and 0ml. get the resistance through an ohmmeter. So I have a max and min value of the resistance. This is max (1.58?) and min (0.31?). Then I work out the middle value of it (max+min)/2= (1.58+0.31)/2=945?. I find the closest fixed resistor which is 948?. To validate I used voltmeter find the voltage cross fixed resistor and the sensor when the water at max level. 2.25v and 4.27v which is close to the value it should be. at max level the sensor should get two times the voltage than the fixed resistor. Because this is a potential divider (voltage share = resistance share) there is more resistance on the sensor so more energy is needed to pass the resistor therefore more voltage they get.

For reading, I need to remember when I read the level of water or any liquids, I need to read the dip of water level and my eyes should at the same level as the dip of water.

I won’t use any data which are not very accurate. All my results and calculations will be in 2 significant figures.

Safety

My circuit is perfectly safe because before doing the research I checked every wire and found there was no problem. The power supply was the batteries which were 1.5V for each and I got 4. So the total voltage was (1.5*4)V which was less than 38V, so it was safe for humans. The water was clean and it was not harmful to people. The beaker was 1500ml big, but I only used 1000ml, because if I used 1500ml the water would easily overflow.

Experiment

I connected the equipments and checked does each one work well and turned the voltmeter to 20. Then I started my experiment. I put 100ml water into measuring cylinder and looked the dip of the water to make sure it is accurate. Then I poured them into the beaker. I took down each voltage for corresponding water level. I took 3 set of reading so I could have an over all average latter on.

Then I got two rulers to measure how high each ml was and tried to make it more accurate, I put one of them in the beaker and another one at outside which was used for measure. Because the base of the beaker was not horizontal so the first one was used to make sure the second ruler got the right position and could make the inaccuracy smaller.

There was about 0.8cm per 100ml. So I can calculate the height of any levels and reduce the inaccuracy.

Problem ; Improvement

Firstly, there was a big problem I find. As soon as I pour the water in, the handle went opposite direction. So my reading of the voltmeter decreases. So I pour the water up to 1000ml first then taking water out from it each time. This dose take me a bit time but I managed in the end.

Secondly, the voltages would change by the position of the beaker and if it was closer to the stand, the voltage would be smaller because when the position changed, the position of the float changed as well. During the experiment, somebody including myself touched the beaker a little bit, and then I just got an inaccuracy.

Thirdly, in the experiment I found sometimes when the water level went up, the voltage went down. Normally it should go up because when the resistance was bigger, the voltage was increase. Then I found the reason. Sometimes when the level went up, the float moved to forward. Then it pulled the joint so the resistance was smaller.

Lastly the float always collides the wall of the beaker, so when the water level went up, the float didn’t work regularly and it affected my result of the voltage.

I support to solve the third problem in this way: I changed the float to a small ball, because the mass of the ball distribute symmetrical, the problem can be solved. Then I did the experiment in this way and the same problem did not happen. So the results were more accurate.

And if the beaker position changed, whatever the position of the float of the ball would be changed dramatically. So the results would be error and I need to do the experiment again. So I just put the beaker close the wall and if the position changed, I did not use the data for my investigation.

For the last problem, I just used my hands to move the float to the middle of the beaker. So far, the new problem would occur, because of moving the float, the position of the float would change all the time, so I should collect the data after a bit while waiting until the float stop moving any more.

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