##### Liquid level based on flotation and a rotary potentiometer

By using a rotary potentiometer connected to a cylindrical float plastic, measure the water level in a tank filling with water, as the water level moves up, the float attached to the rotary potentiometer will moves accordingly as it floats on top of the water. Find out the relationship between the volume of water and the voltage using the potentiometer as it move accordingly with the level of water.

Rotary potentiometer – Movement to cause change of voltage

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Float arm – Connect the polystyrene to the potentiometer

Circular Polystyrene – Moves as level of water goes up

Measuring Cylinder – Measure the amount of water added

Digital Meter – Measure the voltage across the potentiometer

Clamp – Hold the potentiometer above the tank

Tank – Contain water

Power pack – Supply power to the potentiometer

Protractor – Measure the angle of the float arm movement

The Sensor

Potentiometer – A variable resistor that functions as a voltage divider.

Measurements to record in the experiment:

Volume of Water added each time

Angle of Movement of the float arm

Voltage across the Potentiometer

I am going to take these three measurements to investigate the relationship of the volume of water and the voltage of potentiometer when water is added to the tank.

As the tank is rectangular shape, the volume of water is proportional to the height of water, which makes it easier to measure the volume of water instead of the height of water as the amount can be clearly recorded each time water is added to the tank.

Polystyrene is a light weight material which has a lower density than water meaning it will maintain its position on top of the water. I am going to use a cylinder shape polystyrene cylinder to attach to the float arm and cause the potentiometer to move as the ball move along the water level.

The set up and the circuit diagram:

Tank filled with water, Clamp stand holding the potentiometer on top connected to the polystyrene. Potentiometer connected to low voltage supply and digital meter.

A 5V Power Supply from the low voltage supply connecting to the Sensor (potentiometer 10K ?) A Voltmeter (digimultimeter) connected across the potentiometer to measure the voltage

Water is added per 100ml in tank which cause movement to polystyrene.

Safety

As the experiment involves water and electrical power supply, electrical components have to be placed away from water to avoid danger. The circuit should place away from the tank and plastic cover to be covered over metal connection and the low voltage supply unit is also covered in plastic.

Difficulties

When connecting the polystyrene, I used a metal rod to attach to the potentiometer. The metal was firmly attached to the polystyrene on one end by glue. The other end was bent to make it a hook shape to hook onto the potentiometer. It was not secure enough to cause the potentiometer to move during the preliminary try out as the water was added. The metal stick and the polystyrene moved as water were added but not the potentiometer. I had to clamp the metal to make the hook more secure attach to the potentiometer in order to make the potentiometer turn as the water is added.

Prediction

As the polystyrene is lifted by the water, the arm will turn the potentiometer increasing its resistance and causing the voltage across it to decrease. The amount is uncertain but it should show a strong relation between the amounts of water. I decided to use 5V on the power supply as input voltage which gives measurement voltage on the digital multi meter to 2 decimal places.

Results from experiment

Voltage (V)

Change in Voltage (V)

Volume of Water ML (+/- 10 )

First Experiment (+/- 0.5)

Second

Experiment

(+/- 0.5)

Average Results ( +/- 0.5)

First Experiment (+/- 0.5)

Second Experiment (+/- 0.5)

Average Results (+/- 0.5)

Angle (Degree) (+/- 0.5)

Height (CM) (+/-0.5)

2000

1.14

1.14

1.14

0

0

0

0

5

2100

1.12

1.13

1.125

0.02

0.01

0.015

1

5.5

2200

1.12

1.07

1.095

0.02

0.07

0.045

2

5.6

2300

1.12

0.95

1.035

0.02

0.09

0.055

4

5.75

2400

1.11

0.99

1.05

0.03

0.15

0.09

9

5.9

2500

1.04

0.97

1.005

0.10

0.17

0.135

13

6.2

2600

0.98

0.89

0.935

0.16

0.25

0.205

16

6.5

2700

0.94

0.81

0.875

0.2

0.33

0.265

20

6.8

2800

0.90

0.71

0.805

0.24

0.43

0.335

23

7

2900

0.91

0.69

0.800

0.23

0.45

0.34

25

7.12

3000

0.85

0.67

0.76

0.29

0.47

0.38

30

7.6

3100

0.82

0.64

0.73

0.32

0.5

0.41

32

7.8

Results

The change of voltage is the voltage compared to the first voltage measured when the polystyrene was centered. Instead of using the actual voltage value, I used change in voltage because the values can be more clearly noticed when comparing to the volume of water. As the volume of water increases, the change in voltage increases. Meaning the polystyrene has driven the potentiometer to a different position every time water is added which cause the polystyrene to float higher as it stays on top of the water.

Angle moved from the float arm showed proportional to the change in voltage. The angle change is caused by the movement of polystyrene ball. The change in voltage and angle overall was not as much as I expected. This is because of the polystyrene’s ability to cause how much the float arm to move. As the length of the arm remains same, the polystyrene would not remain floating at its center point. In theory, the angle should get less and less as it is going up more steeply and the ‘ball’ is no longer center. I have drawn a diagram to explain the situation:

The results overall has proved my prediction to be correct as more water is added to the tank, the voltage across the potentiometer decreased caused by the movement of the float arm. The graphs illustrate the trend line shows that the result does fit but not entirely due to inaccuracy of the experiment. The tightness of the float arm connecting the potentiometer was the main problem as slippage occur during the experiment which have affect some of the data. From the graph it is seen that water from 2400 to 2800ml it has a bigger voltage which is cause by the different smoothness and slippage of the potentiometer at different point. It is difficult to completely secure the float arm to the potentiometer.

Each time when water is added the ball move upward, but the arm’s length remain the same meaning more part of the ball is going into the water and the angle get less every time. Which means the length of the arm will affect how much the potentiometer rotates. How well the polystyrene float against water is also a factor that could affect the potentiometer.

– Volume of water – because of the properties of the Polystyrene, every 100ml of water added would lift the polystyrene to a high position. Which the float arm would be at a different angle as more water is added as seen in the diagram.

-Length of the float arm – this is a significant factor to the change in voltage of the potentiometer and the amount of movement. The contact point of the float arm with water is different when water is added each time. Which mean the angle which the potentiometer was moved at each point is less than its previous one and are slightly smaller than it should have been.

These main factors that affect how much the potentiometer would rotate.

After looking at the result of the voltage and volume of water, there is a strong correlation between the height/volume of water and the voltage of the sensor (potentiometer). The measure was not highly accurate as many factors could be altered without noticing (e.g. tightness of the arm to the potentiometer, slippage)

The sensor is not very sensitive to change overall, the largest change in voltage was

0.41v and the water level was 1100ml more. The small change in voltage was cause by the length of the float arm. A longer float arm would cause greater change in voltage as it creates a bigger angle every time it moves. The moment would be bigger through a larger angle, thus create a much larger change in voltage. Calibration of the sensor is difficult as they are more than one variable from this experiment. Supposing there should only be one variable which affect how much the float arm rotates, which is the volume of water which cause the change in height of water within the tank. However the length of the arm is also a variable. A larger resistance potentiometer could be use to improve its sensitivity which would give out a larger amount of change.

The sensor can be used to measure different liquid level (water , oil, etc) in different industries, when water levels drop below certain level the voltage change could trigger a device which to release more water into the tank. It could also be applied in assisting household where an alarm is set when the water level in a bath/sink has raise to a certain level as a warning.

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