Weighing Scales

Basically there are three types of weigh scales-

• Balances
• Analog scales (mechanical scales)
• Digital scales (electronic scales)

Balances: These are the earliest form of weighing equipment. A known weight is placed on one side and the object to be weighed on the other side. Method is comparison of weights and approximate.

Analog Scales: Scales are advanced compared to balances. The object is placed on the scale and the pointer shows the weight on the graduated dial. Weight measurement is precise compared to balances.

Digital scales: Precision is what these scales are known for. Electronic scales have extra features such as display weight in multiple units (kilograms and pound), cost calculation, counting number of pieces, or can be hooked up to a computer to store time/material/weight information which can be used to generate reports.

Mechanical scales are almost obsolete. Digital scales cost lesser. Unlike mechanical scales, electronic scales do not have moving parts hence maintenance cost is lesser. Also electronic scales have self calibration feature. Calibration is the act of checking or adjusting (by comparison with a standard) the accuracy of a measuring instrument.

There's a fourth type called Hybrid Scales or Electromechanical scales. These are mechanical scales converted into electronic by inserting a load cell in the weight transfer lever. These scales have an electronic scale's advance features but also have the disadvantages of a mechanical scale- moving parts & maintenance issues.

Commonly used units of weight are-

Grams (g) and Ounces (oz) - 10g of an expensive spice or 500g of wool

Kilograms (kg) and Pounds (lb) - 5kg rice or 20lb coal for your barbecue or your own body weight

Quintal - a small car weighs around 8 quintals or a large horse could weigh around 4 quintals

Ton (T) - a sport utility vehicle weighs about 1.5T or Indian elephants weigh between 4T and 7T

Weigh scales are built for a certain range of weight called the rated capacity. An object weighing 80kg cannot be weighed on a 50kg scale. So how can one know the weight before weighing?? Of course scales are over-load protected. Most scales are built to take 150% of the capacity. However accuracy cannot be guaranteed beyond the rated capacity.

Accuracy is defined as "the ability of a measurement to match the actual value of the quantity being measured".

Precision is defined as a. the "ability of a measurement to be consistently reproduced" and b. "the number of significant digits to which a value has been reliably measured".

Click Accuracy and Precision to know more.

.........