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# The aim of this investigation is to design, build and test a sensor.

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Introduction

Sensors Coursework Aim and Hypothesis The aim of this investigation is to design, build and test a sensor, which has an appropriate: * Sensitivity * Response time * Resolution * Range * Minimum random/systematic error The sensor I have designed operates by detecting the intensity of light using an LDR (light Dependant Resistor), also known as a photoconductor, in a Potential Divider circuit. In this experiment my input variable will be the mass of milk powder added to 750ml of water. My outcome variable will be the potential difference across the normal resistor (which changes as the resistance varies). I will be measuring this using a multi-meter of resolution 0.01V. This will be positioned as shown in the circuit diagram below. Background A potential divider is a resistor or a chain of resistors connected in series in an electrical circuit. It is used to obtain a known fraction of the total voltage across the whole resistor or chain. When a variable resistor, or potentiometer, is used as a potential divider, the output voltage can be varied continuously by sliding a contact along the resistor. Devices like this are used in electronic equipment to manipulate factors such as volume, tone, and brightness. In this case I have used a potential divider comprising of an LDR and a fixed resistor. ...read more.

Middle

> Glass Beaker - I decided to use a glass beaker as it is transparent. The beaker I will use had a capacity of 1litre. As I am using water in conjunction with electricity, I will only fill the beaker with 750ml to reduce the risk of any spills. > LDR & Resistor - I have used the LDR to detect the levels of illumination in the experiment. I decided on this resistance of LDR and Resistor as they are of very close values and produce a potential divider circuit of appropriately high sensitivity. > Wires - Used to connect circuit components > Voltmeter - I used a digital voltmeter for increased accuracy. Using this I measured the potential difference across the normal resistor, which will vary as the LDR is exposed to different intensities of light. > Lamp - I used this as the means for illumination (in circuit below). The first stage of the experiment is to fill the beaker with 750ml of water. The light bulb and LDR are placed so that they are touching the beaker on opposite sides. I will ensure that this is the same throughout the series of readings. Paper is put on either side of this apparatus to ensure that minimal surrounding light penetrates, and minimal light from the bulb escapes. ...read more.

Conclusion

This resolution limit could be improved by taking measurements to a higher number of decimal places, which would require more advanced equipment. Range My average result values range from 0.32v to 1.28v. This is the largest possible range with the available equipment as shown in the preliminary experiment. If possible, I would have used a fixed resistor of a slightly closer value to the LDR. This would have produced a higher sensitivity and a wider range. However, this range provides a suitable set of results to reinforce the theory of this sensor. Sensitivity The graph illustrates that the sensitivity of the sensor decreases as the intensity of incident light decreases (as more milk powder is added). This is shown by the levelling off curve. As the resistance of the semiconductor decreases, there are increasingly more conduction electrons within it. There is a limit to the capacity that it can hold, so it will be able to hold less and less until in can't hold any more. This will be the point at which the line completely levels off. Response Time The response time of my sensor is very quick. However, the procedure that I carried out required me to wait for the water to settle. This may not be the case if it were used in real life. Conclusion In this investigation I have successfully designed, built and tested a sensor which produces results with a. ...read more.

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