To build and calibrate a sensor in order to calculate the temperature of surroundings.

Authors Avatar

                                                                                           

Using a thermistor as a temperature sensor

AIM: To build and calibrate a sensor in order to calculate the temperature of surroundings.

METHOD

Firstly I assembled all of the apparatus shown in the diagram. I then heated some water in a kettle, and poured it the big beaker. Next I lowered the beaker containing the ethanol into the hot water, with the thermistor just below the surface of the ethanol. I took the voltmeter reading for every 5 degrees Celsius as the temperature of the ethanol rose. I then added ice to cool the water down, again taking readings as the temperature of the ethanol declined. I repeated this experiment three times and took averages for each of the temperatures recorded.

FAIR TESTING

To ensure the test was entirely fair, I made sure that the same thermistor was used for each experiment. I also used the same volume of ethanol to ensure this had no effect on the result. The same thermometer was also used for the same reason. The potential difference delivered around the circuit was kept to a constant three volts, and I used the same fixed resistor to ensure that the potential difference split evenly across the resistor and thermistor, which would have severely affected my results.

SAFETY ASPECTS

The main safety aspect to consider whilst doing this experiment involved the use of ethanol in the experiment, especially as I planned to heat it. As ethanol is flammable, I could not heat it with a naked flame, due to obvious fire risks. So instead I chose to use a water bath, using water I had heated to heat up the ethanol without the use of a flame. This lead to another risk, as electricity and water were both present in my experiment. I kept electrical leads well away from the water, and where the leads had to come near to the water to insert the thermistor into the ethanol, I used a clamp and clamp stand to keep the leads above the water level, so no water could be spilt on them.

        The other main problem was the hot water. If spilt, it could have caused some serious injuries, so I made sure that it was not concealed in anyway so it would not be knocked over. Also, when filling the beaker with beaker with the hot water, I held the beaker with a piece of cloth to avoid burning by hands.

BASIS OF MY EXPERIMENT

 In my experiment, I have set up a potential divider circuit by combining a thermistor and a fixed resistor in series. This causes the potential difference to split across each component, with the amount of potential difference splitting across each component depending on its resistance. In my experiment, I started with the component having equal resistances at room temperature, causing the potential difference to split equally over each component.

Join now!

        The resistance of the thermistor depends on the temperature. If the temperature is increased, the resistance of the thermistor would decrease, thus decreasing the amount of potential difference across the thermistor. To do this I needed to find a way of regulating the temperature. Heating water and putting the thermistor into this was out of the question as the water could interfere with the circuit, so I chose ethanol Therefore if the potential difference across the thermistor is measured at different temperatures, it would become possible to measure the temperature using the potential difference across the thermistor.

INITIAL EXPERIMENTS ...

This is a preview of the whole essay