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Measuring the temperature in a greenhouse using a thermistor.

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Introduction

Measuring the temperature in a greenhouse using a thermistor

Aim

I have decided to measure the temperature of a greenhouse using a thermistor in a potential divider circuit. A thermistor is a temperature sensor whose resistance will increase or decrease with temperature change depending on what type of resistor.

An alternative for this experiment could have been measuring light levels in a greenhouse using an LDR. A light sensor in a green house could tell you when and where in the greenhouse the most intense sunlight is, which you could you use to aid your growing skills.

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.

I have decided to use a 100K NTC precision thermistor as it can measure a range of temps from – 50 to 110 degrees C, and in Britain temperature range from around –10 to 50 degrees C, so my thermistor will cover these ranges.

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Middle

To measure response time I will up two beakers one at a hot temperature and the other at a cold temperature. I will then place the thermistor into the cold beaker, until it reaches a stable output voltage, then I will put it in the hot beaker and time how long it takes for the thermistor reach a stable output voltage in the hot beaker. I will then repeat this going from hot to cold. Here I will be looking for speed in reaching a stable result and also differences in going from cold to hot and hot to cold.

To measure drift I will put my thermistor at room temperature and measure the output voltage every 10 seconds for one minute. Here I am looking for any anomalous results before the output voltage is stable.

Safety precautions will be taken into account throughout the experiment and goggles will be worn, hair tied back and apparatus set up carefully.

Results

The sensitivity of a measuring system is the ratio of change of output to change of input.

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Conclusion

When I was measuring drift it did take 30 seconds to reach a stable reading but in the situation for which I want my sensor that sort of time is appropriate as extremely accurate readings are not necessary. The fluctuations were also very slight so it wouldnt effect results.

When measuring response time it took longer to go from cold to hot than it did to go hot to cold. It was a lot more responsive to the change to cold as also it is with sensitivity which will is good for my sensor as I need to know sooner when cold temperatures are coming.

After analysing certain aspects of my sensor I believe it to be it to be good enough to be used in measuring temperatures in a greenhouse as its sensitivity is accurate enough and drift and response time are also quick enough. Although this is not the most accurate sensor for this job it is good enough another one may be used if more accurate work is being done.

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