• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Sensor Project

Extracts from this document...


Sensor Project


In this project I am going to test and evaluate a thermistor. I am going to test the thermistor on how the resistance of this component changes under different temperatures. Thermistors are thermally sensitive resistors and have, according to type, a negative (NTC), or positive (PTC) resistance/temperature coefficient. A thermistor is a type of resistor whose resistance changes significantly when its temperature changes.

A negative temperature coefficient (ntc) thermistor has a resistance that decreases with increase of temperature. This is the most common type. This is the type of resistor that I shall be evaluating and will be using in my experiment.

A positive temperature coefficient (ptc) thermistor has a resistance that increases with increase of temperature. The resistance of a semiconductor generally decreases with increase of temperature. Semiconductors are therefore used to manufacture ntc thermistors.

When the temperature of a semiconductor is increased, the number of charge carriers increases as more valence electrons gain sufficient energy to break free from atoms to become conduction electrons. The number of charge carriers increases as the temperature is increased so the resistance of the semiconductor falls. Semiconductors are used to make a wide range of electronic devices including electronic chips, light emitting diodes and solid state lasers. Communications, commerce and entertainment have been revolutionised as a result of semiconductor devices.

...read more.


Composite Thermistors can be custom-designed to match the electrical and thermal characteristics of gauges and probe housings.

Thermistors are used in temperature sensors and digital thermometers in systems when the resistance needs to drop drastically under a small amount of temperature change. An example of a system when a thermistor is needed is in incubators, when the temperature needs to be controlled and the temperature needs to be kept totally constant. If the temperature inside begins to decreases then the resistance will increase, therefore the cooling system will stop producing cold air so much. If the temperature begins to increase then the thermistor’s resistance will decrease, therefore the cooling system will work more, thus keeping the temperature inside the system constant. Another context in which thermistors are needed is inside mobile phones. The components inside the phone, which are all needed to make the phone work, will only work at a certain temperature. If the temperature of the phone gets too high some of the components may break. Mobile phones have a system using a thermistor, when the temperature of the phone gets too high the thermistors resistance decreases allowing the system to work. The mobile phone automatically shuts down and switches off, allowing all the components to cool down. This stops the owner needing to get the phone repaired.


...read more.


The input signal may fluctuate or the sensor itself may generate noise. Small unsystematic variations are present in all experimental data. Their size limits the precision with which a measurement can be made. Taking an average over repeated measurements can improve the final result, as long as the conditions can be kept the same. This is why I took recordings when the thermistor was in an environment when the temperature was increasing and then decreasing, this gave me two sets of recordings which allowed me to check my results were correct.

Systematic error is very hard to detect, because detecting it means making another, even better, measurement. Systematic errors include zero error, and error due to disturbing influences, for example temperature. My experiment controlled the temperature and therefore this will not have been a factor.

Therefore I can conclude that my thermistor performed fairly well, this is because the results followed a pattern, my thermistor performed successfully because the response time was good, there was an unsystematic error when the multimeter reading was fluctuating and therefore I can conclude that my readings were fairly accurate.

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. Investigate how the temperature affects the resistance of a thermistor.

    resistance because there is less energy to transfer the electrons to the conduction band and so it is hard for the electricity to travel because there are less electrons to move. Variables: There are a variety of factors that could affect the results of my experiment into the resistance of

  2. Investigate the variation of the resistance of a thermistor with different temperatures.

    Hypothesis I predict, therefore that the resistance in any experiment will rise as the temperature of the water falls. Results Temperature Resistance Resistance Resistance Resistance (C) (Ohms) (Ohms) (Ohms) (Ohms) 1st Results 2nd Results 3rd Results Average 90 70.7 72.1 77.2 73.3 85 81.2 79.3 87.2 82.6 80 88.9 84.2

  1. Experiments with a thermistor

    thermistor Thermistor Probe 1- 20 --> 100oC 7.78 21.18 2- 20 --> 100 oC 7.83 20.09 Average 7.80 20.64 From the values taken, it can be deduced that the bead thermistor was better of the two in terms of response time because it took the shortest time to show a steady value when a sudden change in temperature was applied.

  2. The effect of temperature on the resistance of a thermistor

    Then I had finished the first set of readings I restarted the experiment for a second time in order to average them out for more accurate results. Results: Start temp (c) Current (A) Volts (V) Resistance (I) Average (I) 0 1)

  1. Characteristics of Ohmic and non-Ohmic Conductors.

    From the results, I can see that Current increases with Voltage for all the graphs. But the way in which it increases is different. Any difference in reading may be due to some error, which I will account for in evaluation.

  2. Investigation into how the resistance of a thermistor varies with temperature.

    10.9 31� 1.6 3.1 4.6 4.4 9.2 13.9 36� 1.6 3.0 4.5 5.1 10.0 15.7 41� 1.5 3.1 4.7 6.0 12.3 18.4 46� 1.5 3.1 4.3 6.2 12.8 18.3 51� 1.5 3.1 4.5 7.6 15.6 23.0 56� 1.5 2.9 4.5 8.4 15.9 25.5 61� 1.5 3.1 4.5 9.3 19.0 28.3

  1. Investigating a Thermistor.

    I then could have positioned the hairdryer at different distances from the thermistor (creating different temperatures). However, due to the fact that the air is a poor thermal conductor I decided to small beaker of use distilled water (as it is a poor electrical conductor and as explained below the temperature can easily be kept constant throughout the beaker).

  2. Investigate the relationship between temperature and resistance in a thermistor.

    I will light the Bunsen burner and when the temperature reaches 250C will read the current through the thermistor and the voltage across it and record them. I will do this at each 50C interval up to 1000C. I will repeat the whole experiment three times to achieve the most accurate results I can.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work