Making, Calibrating and Testing a Sensor

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AS Instrumentation Task

Making, Calibrating and Testing a Sensor

Introduction

The aim of my investigation is to produce a working sensor for use in any application of my choice. In order to do this you were required to choose a task for my sensor to carry out, and then choose an appropriate sensor to carry out the task. The sensors available for selection are an LDR, a linear resistor and a thermistor. However, for the sensor to be fully operation in its application it will be to be used alongside a resistor to give the right amount of sensitivity for the task, therefore I must also select a resistor. Then you must conduct an experiment to allow me to calibrate my sensor to make a fully functioning sensor.

Description

The scenario for which I have chosen to design my sensor for is for use in a garage. When cars park into garages it is useful for the cars to know when they are getting close to the end of the garage, in order to allow them to stop safely without being to close to the end of the garage where they might crash or not inside of the garage enough thereby meaning the garage door will not close.

Method

In order to produce a fully functioning garage sensor an LDR is going to be used. The way the LDR will work within my sensing circuit is it will be placed at the end of the garage and there will be a light mounted at the opposite end of the garage. Then as the car drives through the garage the LDR will sense how close the car is by sensing how much light is hitting the LDR. The more light reaching the LDR, the further away the car is. Once the car has reached the maximum point it can safely park a buzzer will sound and the driver should park his vehicle.

The circuit will be used on experiments to select a resistor for optimum sensitivity, calibrate the LDR's operation and measure the resolution of the sensing circuit. In my experiment for selecting a resistor with the maximum range of sensitivity, many different resistors will be used, in conjunction with an LDR. I will then connect the LDR to a multimeter which will measure the voltage across it. Then to test the range of sensitivity i will measure two values, the two extremes an LDR will have to deal with. The first being the dark so the LDR will be completely covered, blocking out all light and this will give me a minimum value and then the light where the light will be allowed to shine fully on the LDR giving me my maximum value. Then the range will be calculated by taking away the value of the measurement in the dark, from the measurement from the light. This will give me my range and the largest figure; will be the LDR which gives me the largest range.

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Next to calibrate my sensor the voltage will be measured on a multimeter from different distances from the LDR. I am going to set up the experiment in much the same way as testing for the resistor. However a fixed resistor will be used, that would have selected in my first experiment. Then as opposed to testing only light and dark, the sensitivity will be tested from a distance of 30cm back using a piece of card to replicate the car and a lamp to replicate the light, then the piece of car will be moved forwards at 1cm ...

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