PHYSICS PROJECT REPORT ON PHYSICAL BALANCE
An analytical balance (often called a “lab balance”) is a class of balance designed to measure small mass in the sub-milligram range. The measuring pan of an analytical balance (0.1 mg or better) is inside a transparent enclosure with doors so that dust does not collect and so any air currents in the room do not affect the balance’s operation. This enclosure is often called a draft shield. The use of a mechanically vented balance safety enclosure, which has uniquely designed acrylic airfoils, allows a smooth turbulence-free airflow that prevents balance fluctuation and the measure of mass down to 1 μg without fluctuations or loss of product. Also, the sample must be at room temperature to prevent natural convection from forming air currents inside the enclosure from causing an error in reading. Single pan mechanical substitution balance maintains consistent response throughout the useful capacity is achieved by maintaining a constant load on the balance beam, thus the fulcrum, by subtracting mass on the same side of the beam to which the sample is added.
Electronic analytical scales measure the force needed to counter the mass being measured rather than using actual masses. As such they must have calibration adjustments made to compensate for gravitational differences.They use an electromagnet to generate a force to counter the sample being measured and outputs the result by measuring the force needed to achieve balance. Such measurement device is called electromagnetic force restoration sensor.
Triple beam balance
Triple beam balance is an instrument used to measure mass very precisely. The device has reading error of +/- 0.05 gram. The name refers to the three beams including the middle beam which is the largest size, the front beam which is the medium size, and the far beam which is the smallest size . The difference in size of the beams indicate the difference in weights and reading scale that each beam carry. The reading scale can be enumerated that the middle beam reads in 100 gram increments, the front beam can read from 0 to 10 grams, and the far beam can read in 10 gram increments. The triple beam balance can be used to measure mass directly into from the objects, find mass by difference for liquid, and measure out a substance. The parts of triple beam balance are identified as the following.
- Weighing pan – The area in which an object is placed in order to be weighed.
- Base – The base rests underneath the weighing pan and can usually be customised to fit on a workbench or set up with tripod legs.
- Beams – The three beams on the balance are used to set the level of precision, with each beam working at different increments (1-10 grams, 10 grams and 100 grams). When using the triple beam balance, it is recommended that your start with the lowest level of precision e.g 100 gram increments and then work your way down. For example, if your object weighs 327 grams the 100 gram pointer will drop below the fixed mark on the 4th notch (400g), you will then need to move this back to the third notch (300g). This process will then need to be repeated for the 10 gram increments (20g) and then single figure units (7g).
- Riders – The riders are the sliding pointers placed on top of the balance beams to indicate the mass in grams on the pan and beam.
- Pointers – The scale pointer marks the equal point of the object’s mass on the scale and mass on the beam
- Zero adjustment knob – This is used to manually adjust the triple beam balance to the ‘zero’ mark (check to ensure that the pointer is at zero before use).
Before using triple beam balance, the scale pointer should be at zero.The zero adjustment knob can be used to adjust the scale pointer. Place the objects on the pan and adjust the riders. The hundred rider should be initially adjusted and follow by the tens rider. Adjust the ones rider until the scale pointer is at zero again.