Physics - Rotary Potentiometer

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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
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Circuit Diagram:

Safety

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 ...

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