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# Linear position sensor and Mass.

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Introduction

Linear position sensor and Mass The task that I have chosen is to build and test my own sensor. I reasoned on designing a sensor that could be used to measure mass and in turn force. The component that I intend to use for this sensor is a linear potentiometer (i.e. linear position sensor). The potentiometer can only detect change in potential difference so the numerical value, which I obtain from the potentiometer, should correspond with a specific mass. I will use a table and a calibration graph to show my reading clearly and accurately. The graph can then be used to give a mass value when we are given a value of the potential difference. How liner potentiometers work. Diagram of a linear type potentiometer: Resistor Moving contact Input V V Output V a fraction of input V As the moving contact is moved up or down the resistance the output voltage changes A liner potentiometer works like a chain of resistors. Because there are 5 resistors then the Output = a fraction of the resistance Of input Moving Contact Output voltage For instance, say if the voltage input was 10v and there were 5 resistors and the moving contact was on the 3rd resistor up from ...read more.

Middle

The straight line can be explained using the physics involved in a linear resistor and potentiometer. A mass potentiometer consists of a linear resistor, on which a moving contact is put on. The resistor and the contact are placed in two circuits so that a value for the output voltage is gained via the position of the moving contact, on the linear resistor. I was given the straight line due to my choosing of the steadily increasing mass. (I.e. each 10g that added the value of the output voltage increased steadily) Therefore I can say that the resistance increases steadily in proportion to the mass acting on the moving contact. This is supported by the graph. The output voltage values starts to level out towards 700g. This can be explained by knowing the factors of the sensor. The potentiometer that I used has an operating force of 2N to 7N (200g -700g) and a mechanical travel of 12.5mm. This means that the moving contact has reached the maximum travel, at this point maximum resistance is being encountered and the output voltage stays the same. EVALUATION: I feel that the experiment was successful in that I obtained fairly reliable results that gave me a clear outcome. ...read more.

Conclusion

This voltage reading then triggers off the sound system. The moving contact is small on my sensor so it would not be suitable for a burglar alarm because there is less chance that an intruder would manage to make contact with it. Therefore the pad / moving contact must have a large surface area increasing the chance of an intruder stepping on it. The sensor has a virtually instantaneous response time. This aspect is crucial for a burglar alarm pressure pad because the intruder could tip toe across the sensor quickly and the sensor has to be able to be rapid enough to be effective. Problems may occur if the sensor was programmed to respond to any mass. If the sensor was placed in the house a household pet such as a cat or dog easily triggers it. Therefore the sensor system must be modified to take into account the mass of household pets. Setting the alarm to respond to a certain optimum voltage could do this. E.g. anything less than 60Kg could walk on the pad without setting the alarm off. This system has an advantage over infrared-based alarms because it could be activated or turned on with the pets in the house/room. ...read more.

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