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Building and testing a sensor to determine number of degrees to which a window is open.

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Introduction

Alex Furber 12HW Sensing Project 20-02-02 Building and testing a sensor to determine number of degrees to which a window is open INTRODUCTION When making use of a greenhouse to grow plants out of season or on a large scale for commercial reasons, the temperature within the green house must be carefully regulated, in order to ensure that the plants are under the optimum growing conditions. With the windows shut permanently, the temperature may become too high, and the windows need therefore to be opened. This will allow the temperature to drop back to the correct level. Different numbers of degrees to which the window is open have different cooling effects. For example, if the window is open by 50 degrees, then there is probably a more rapid cooling effect upon the greenhouse than if the window was 10 degrees open. Thus, it is important to know how many degrees the window on a greenhouse is open. It could however be very time consuming for people to check the greenhouse(s) manually, or particularly problematic if the temperature should become a problem during unsociable hours. It would be extremely useful, then, if a sensor could be attached to the windows of a greenhouse, and a reading sent back to a control room as to how open the windows are. Someone could then either use a motor attached to the window to alter the setting, or adjust the window manually. My sensor could be used in conjunction with a number of other sensors, e.g. temperature sensors and moisture sensors, to send all the required reading back to a control room, thus allowing the control of the climate within in the greenhouse to be totally automated. Above: a typical greenhouse Alex Furber 12HW Sensing Project 20-02-02 PLAN There a number of ways in which a sensor could be built to measure the angle at which a window is open. ...read more.

Middle

If on the other hand it were too big, then the increase in voltage for every 10 degrees would be much too small, and difficult to detect. When at maximum resistance, the rotary potentiometers resistance is 5000 ohms, therefore a suitable fixed resistor would have a value of about 1000 to 2000 ohms. I will be using a fixed resistor of 1200 ohms. The results of my experiment are shown below, in the results section of my project. RESULTS CIRCUIT 1: The following results are my results for circuit 1. For a diagram of circuit 1, refer back to page 5. 3 Volt supply 6 Volt supply Degrees Volts Degrees Volts 0 0.00 0 0 10 0.10 10 0.24 20 0.22 20 0.5 30 0.31 30 0.74 40 0.43 40 0.97 50 0.56 50 1.15 60 0.62 60 1.36 70 0.72 70 1.72 80 0.84 80 1.93 90 0.93 90 2.17 100 1.01 100 2.43 110 1.09 110 2.72 120 1.20 120 2.98 130 1.29 130 3.11 140 1.31 140 3.34 150 1.34 150 3.59 160 1.44 160 3.81 170 1.56 170 3.97 180 1.61 180 4.23 I will now present my results on a calibration graph, showing the number of degrees that the rotary potentiometer has turned against the number of volts across it. This will allow me to observe the linearity and sensitivity of the sensor with the two different voltage supplies. This graph can be observed on the next page. ANALYSIS The graphs show that my sensor is fairly linear, for both of the voltages. This is indicated by the fairly straight nature of the graphs, for both voltages. Although neither graph is completely straight , It is probably not the sensor itself that was at fault but numerous errors that occurred during the taking of the results. These include both precision and procedural errors. From the graphs it can be seen that the line representing the sensor with the six-volt supply is more sensitive. ...read more.

Conclusion

However, the difference in cooling effect between 20 and 30 degrees on the other hand , may be large enough to have a profound effect. My sensor is equipped to detect the openness of the window to within 10 degrees. Thus , in this respect at least my sensor is adequate. The sensitivity of my sensor could be greatly improved. If I were to increase the voltage coming from the battery pack, I could greatly increase sensitivity. My results for circuit 2 showed very non-linear characteristics. Although I cannot be certain as to the reasons for this, I believe it is probably due the heating effect on the fixed resistor within the circuit, as I explained in the previous section. In this case, I estimated a suitable value for the fixed resistance. However in hindsight, I perhaps should have calculated what resistance I required to give me a specific increase in voltage for every 10 degrees. For example, I could in fact have chosen to obtain increase in voltage of 0.2 volts when the total supply was 6 volts for circuit 2. I would then use the equation: R1/ (R1 + 5000) = 3/6. In the equation above R1 is the value of my fixed resistor. 5000 is the value of the resistance of the potentiometer when it is turned to its maximum resistance. The 3 is the voltage I would like the potentiometer to draw when at maximum resistance. This is because this gives me 0.1 volts for every 10 degrees of turn, as the total number of degrees that the potentiometer can turn is 300. The 6 indicates the total voltage supply. R1 = 0.5(R1 + 5000) R1 = 0.5R1 + 2500 0.5R1 = 2500 .: R1 = 2500/0.5 = 5000ohms. This would have been a better value to use as my resistance, and would be an improvement I would consider if doing the experiment again. Overall, my circuit 1 sensor was fit for its purpose when used with a six-volt power supply. It was quite linear and had a suitable resolution for its purpose, of approximately 10 degrees. ...read more.

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