I decided to design a temperature sensor for a greenhouse using a thermistor, as temperature can be critical in growing plants especially if it gets too hot or too cold. As my thermistor is an NTC this means that as temperature decreases its resistance increases, and when temperature increases its resistance decreases. Plan: Circuit Explanation The water is boiled until it reaches a temperature of just above 90i?? Celsius. The thermistor is inserted into the hot water and the voltage across it is measured for a temperature of 90i??.
The varying voltage across the thermistor is measured as the temperature falls at 10-degree intervals. The experiment is repeated and a second set of readings obtained. An average set of readings is obtained and a voltage-temperature conversion graph is plotted. Then test the sensor by attaching the amplifier and relay. Materials/Apparatus Needed: Thermometer, Thermistor, Beaker, Electric kettle, Power supply, Multimeter, Variable resistor, Amplifier, Relay, Leads. These pictures show me testing the thermistor (left), and testing the amplifier to see at what voltage it activates (right).
Variables The volume of water used for this experiment was kept at 250cmi?? The experiment was completed over one day, and on the day, the temperature in the physics laboratory where the experiment took place was 19i?? C. Results Calculation of R1: I want my amplifier to activate at 10i?? C, for the heater to come on. The amplifier turns on at 1. 93V, as I have tested, and because the voltage is proportional to the resistance, I will work out which resister to use using the equation below. (At 10i?? C the thermistors resistance is 124. 8? )