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Building a mass balance to measure small weights (0g-100g) using a rotary potentiometer

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BUIDING A MASS BALANCE TO MEASURE SMALL WEIGHTS(0g-100g) USING A ROTARY POTENTIOMETER Introduction: Nowadays, we have mass balances, weighing scales etc to measure masses but we hardly have devices that measure small masses. Sometimes, we may have to measure objects with small masses say 10g to 100g and my model is created backed up with this idea. Components Used: Digital multi-meter, Meter rule, Retort Stand, Clamp, Rotary potentiometer, Power supply (5V), Spring, Masses (in unit of 10g), 2k and 3k resistors, 1k variable resistor, amplifier. Reason For Choice Of Components: * Rotary Potentiometer: I used a rotary potentiometer so that when masses are placed on the meter rule the change in voltage (output) could be noted. The rotary potentiometer is of 5k Ohms but I connected it to a 5V power supply as a more convenient way of measure. As the potentiometer moves the resistance changes and also does the voltage. * 2k, 3k Fixed Resistor and 1k Variable Resistor: I used these resistors in order to make a Wheatstone Bridge so that there will be a significant change in output when masses are added to the meter rule. * Amplifier: I am using the amplifier in order to make my model more sensitive and obtain a more accurate result. ...read more.


2) When readings were not been taken I ensured that the power supply was switched off. 3) When readings were not being taken, I removed masses from the meter rule in order not to make the spring distorted. 4) When I was not using the multi-meter, I turned it off in order not to run down the battery an give me an accurate result. The electrical cell used was one of a low voltage therefore my working condition was not that dangerous. Experiment: I Hung masses on the meter rule, then record the change in output from the multi-meter. I repeated the process two more times with different masses then found out the average of the readings for more accuracy in my result. I then used my average output to plot a graph. Observations In my initial experiment when masses were put on an inextensible string hanging from the meter rule I noticed that there was no change in the output reading from the digital multi-meter unless heavy masses are put and this system did not produce a sensitive setup this was when I got the idea of the Wheatstone Bridge. The Wheatstone Bridge did not give me a satisfactory result either! ...read more.


Basically this is what I expected i.e. an increase in mass would increase the output produced. From the graph we can determine the mass of object (approximately). To do this place the object on the model and read the output and read of the corresponding mass from the graph and this gives us the approximate mass. FITNESS FOR PURPOSE Resolution: Mass/g(10.00) Output/V +1.00 2.83 +2.00 2.86 Mass/g(30.00g) Output/V +1.00 3.34 +2.00 3.37 Basically, form the table above we can see that when 1.00g is added to known masses, the output is the same for the known mass which implies that 1.00g does not make a difference to the output reading. Moreover, when 2.00g is added to known masses say 10.00g or 30.00g the output changes. Therefore, the smallest change (resolution) my setup can detect is 2.00g. Sensitivity = Change In Output , Change In Input = 0.24 10.00 = 0.024V/g Response Time: This is the time it takes for the output to be detected by a sudden change in mass. In my model the change is almost immediate so the response time is quite fast. Although the last digit on the digital multi-meter fluctuates this only means that the change in magnitude is been resolved. Linearity: My graph (output against mass) is a straight line graph(upward sloping) showing the relationship is proportional(as mass increases, the output increases). ...read more.

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