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Sensors Project Report

Extracts from this document...



1. Aim                                                                 P.2

2. Alternative ways that experiment                                  P.2

3. Plan                                                                                      P.3

4. Variables                                                                                         P.3

5. Precautions                                                                           P.3

6. Preliminary results and Prediction                      P.4

7. Apparatus                                                                     P.5

8. Diagram of the Circuit                               P.5

9. How does a potential divide work?                     P.5

10. Table of results                                                         P.6

11. Calibration Curve – Average Results                   P.8

12. Reliability and Accuracy                             P.10

13. Sensitivity                                               P.10

14. Resolution                                               P.11

15. The error of the experiment                          P.12

16. Improvement of the experiment                       P.12

17. Fitness for the purpose                                            P.12

18. Sources                P.13

Sensors Project Report

Preliminary planning


To measure the number of papers in a pile by creating a very sensitive sensor with the use of resistors

Alternative ways that experiment can be set up

  • Using infra-red sensor by passing through infra- red and determines the thickness of paper and the number of sheets by detecting the amount of infra- red passing through. However, that does not work due to the limitation of equipment
  • Using a balance and determine the number of sheets of paper by mass, but that would not be very accurate due to the fact that the mass of every pieces of paper might vary and the balance is not very sensitive to a tiny amount of change (e.g. only 1 piece of paper is put on)
  • Using a calliper to determine the thickness of one paper and then determine the number of papers there are by dividing the thickness of the pile of paper by thickness of one piece of paper. It is not very accurate because the thickness of paper varies from one side of the paper to another and from one piece of paper to the other.
  • Using a log Potentiometer to determine the number of sheets of paper in the sensor by the thickness of the paper (number of papers) and that varies the ratio of the resistance in the potentiometer so the number of papers can be determined by the ratio.

From all the choices above, the potentiometer is chosen because it is more related to the work in the syllabus and it is one of the most accurate ways to measure among the others that have been suggested. To make the sensor more sensitive, another variable resistor is used to allow it to become more sensitive. The physics will be explained afterwards as a potential divider.


  1. Set up the circuit with two variable resisters, three 1.5V batteries, a multimeter (set up to measure the voltage, in volts).
  2. The circuit will be set up with other variable resister will have the lowest resistance to make the sensor more sensitive so that it can be accurate and experiment will all be done on the same day to get sensible results.
  3. The potentiometer is put vertically so that paper can put underneath however because there is a gap between the slide about 100 sheets of paper thick therefore to set it starting with zero, 2 rulers are put underneath which has equal thickness as 100 sheets of paper.
  4. Then results can be recorded. The experiment is done 3 at least 3 times, and then produces a calibration curve.


  • A variable resistor which will affect the sensitivity of the whole experiment
  • Number of pieces of paper varies from 1 – 200 pieces and is measured when each set of 10 pieces are put on to the sensor to a give sensible set of results
  • The number of batteries only stay at 6V because that gives a steady range for the voltmeter to have readings from 0V => 6V
  • Voltmeter acts like a device which presents the changes that has been made by the different amount of paper
...read more.


make sure all the apparatus works properly (e.g. multi-meter is working properly with enough batteries)prevent getting paper cut from the paperpapers are stacked properly so all the papers are measured by the potentiometer to get more accurate results

Preliminary results and Prediction

The following table show the preliminary results that is tested to show the about trend of the experiment.

Number of papers

Voltage / V






















Main Experiment


  • 1.5 V Battery x 4
  • log scale potentiometer x 1
  • voltmeter x 1
  • variable resistor x 1
  • some wires
  • papers x 200 pieces

Diagram of the Circuit


How does a potential divide work?
A potential divider circuit is one that contains more than one resistor in series. The output to the circuit is taken across a certain number of these resistors and therefore the voltage can be controlled. The amount of voltage is dependent on the ratio of the resistors


This can also be set up with a variable resistor instead of separate resistors. The length of the resistor that has the voltage measured across it will determine the amount of voltage output.


The sensitivity of a sensor can be determined by the ratio of the two resistors. If the fixed resistor is very large in comparison to the detector then small changes will go unnoticed therefore in the experiment another variable resistor is used and is put to the smallest resistance.

The maximum voltage of the sets of results is 5.

...read more.


Improvement of the experiment

It is better to have a wider range of results, to do the experiment with the whole of the potentiometer because in the experiment only small part has been used. Other than that, what should be dependent on is not the number of paper should be both the thickness of the paper and the number of paper.  Then a power supply should be used instead of batteries so it has a higher voltage which helps to increase the accuracy of the sensor. Another thing is a linear potentiometer should be used so readings can be read more easily although a log potentiometer does not give such large values.

Fitness for the purpose

Because the range of the position sensor is from 0N to 6.86N which is too small that we cannot use the position sensor to measure something which give out a lot of sheets of paper (length). So, it is a good choice to use the potentiometer to act like a sensor which measures some thinner sheets. However, we need to overcome the fluctuation of the voltage in multimeters so that we can have a wider range and more accurate results. However generally it can roughly tell the number of sheets of paper so it fits the purpose.


  1. Advancing Physics AS book, Institute of Physics Publishing, Britol and Philadelphia.
  2. Advancing Physics AS 2000 Student version (standalone), Institute of Physics Publishing, Britol and Philadelphia.

...read more.

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