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# Physics - Rotary Potentiometer

Extracts from this document...

Introduction

Can a Rotary Potentiometer be used as a conventional scale?

Introduction

I wanted to find out how a rotary potentiometer could be utilized to work as a weighing scale.  The specific interest is the accuracy of this method and distinguish the advantages and disadvantages of using digital readings instead of our common everyday analogue spring gauge balance at the local supermarket. This investigation will require a potentiometer device being loaded with a series of masses which are linked to a voltmeter measuring the differences in voltage as more masses are added while a spring is used to hold the weight. The benefit of this system is that it can be calibrated in imperial and metric measurements as the results appear in Volts, whereas modern scales only provide ‘grams’ or ‘kilograms’ as opposed to pounds. Accuracy is vital in this task as there is a challenge to see how effective a potentiometer can be, with most spring scales can be accurate up to + or – 1g.

Apparatus

• 6V Battery pack (4 ‘D-sized’ batteries), for ease of use and more energy efficient that a 12v mains power supply
• Rotary potentiometer, attached to a DIY MDF wheel which rotates. It has a spring attachment hole at one end and a mechano shaft for attaching weights
• Expendable Spring, an attachment unit to keep the rotating apparatus together, and the main unit holding weight of equipment
• Digital Multimeter, for measuring voltage differences
• Wires, for construction of circuit
• Weights, each weighing a mass of 10 grams
• Clamp stand, to ensure the potentiometer is stabilised and attaches the spring
• 360˚ Protractor, to measure the angle of rotation done by the MDF wheel

Middle

Working with 6v is relatively safe; the only caution is to ensure wires are making minimal contact to prevent shorting of the circuit. Caution must also be taken when using heavy weights as they have the risk of falling of the table causing potential damage to the floor or the foot. In addition, offloading weights may must be proceeded slowly as a quick unload will mean the instant spring back of the expendable spring may cause an item to strike the eye/face i.e. weight handle. One must also be careful of the spring, as it may unexpectedly snap when on a heavy load.

Measurement Plan

I plan to measure the voltage (potential difference) increase on the multimeter (voltmeter) as weights are loaded on the rotary potentiometer device. The sensitivity of the potentiometer needs to be taken account of as I need to ‘zero’ the readings when setting up the experiment, the expendable spring holding the MDF wheel will no doubt play a part In the resistance of

Conclusion

After I took the voltage readings, I will user a 360˚ protractor to measure the angle of rotation by lining up the shaft with the protractor shaft and placing the centre of the protractor on the centre of the rotating wheel.

Precautions/Errors

Due to human imperfections when constructing the apparatus, one did not consider a catch for holding the expansion of the spring when stretched. This denotes that at heavy loads the spring comes loose off the wheel and I am required to physically re-assemble the spring in its original position after each addition of mass is added.  The spring also sometimes got caught on the imperfections of the MDF wheel, as a result, there were times when the spring reached a level of load at which it stopped stretching until a significant weight is added. In addition, one must consider the permanent deformation of the spring as it is constantly stretched beyond 5 times its length, going beyond its elastic limit may lead to an easier turning of the rotary device. There was also relative nervousness that if the spring would snap under tension.

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