Digital scales represent a significant technological advance over their predecessors, analog scales. Digital scales measure weight by taking advantage of a different method than analog scales. Analog scales rely either on a spring-based or a balance-based method to measure weight. Of the two methods, balance-measuring is the more dependable, since a balance measures an unknown weight against fixed, known weights. The spring method is less reliable, since springs can lose tension and begin giving inaccurate readings. Early digital scales still relied on one of these two methods, and simply gave a digital readout. Modern digital scales, on the other hand, rely on load cells.
A load cell, broadly speaking, is a small node that converts pressure to a digital signal. There are three types of load cells, each using a different physical principle to determine weight. The first type of load cell, the
hydraulic load cell, is based on the principle that, when you increase the weight on a container filled with liquid, the pressure of the liquid will change. Digital scales that use load cells measure the change in pressure of their internal liquid and, from this change, calculate the pressure that was applied to the liquid, giving a readout of weight.
Pneumatic load cells are very similar: they also measure change in pressure. The only difference is that, while hydraulic systems measure a change in the pressure of a liquid, pneumatic load cells measure a change in the pressure of a gas, usually air or nitrogen. When weight is applied to the gas, the gas changes in pressure, and from this change in pressure the amount of weight applied can be deduced.
Strain-gauge load cells operate on a different principle. When a weight is introduced onto a digital scale with a strain-gauge load cell, a structural member or beam within the digital scale is deformed. The deformation of the structural member changes its electrical resistance, and the original weight can be deduced from the change in electrical resistance.
The best
Digital scales are now widely used, everywhere from laboratories to bathrooms. Digital scales can give accurate readings where accuracy counts, sometimes providing measurements down to the tenth, hundredth, or even thousandth of a gram. Naturally, measurements down to the thousandth of a gram are hardly necessary for a bathroom scale, but in industries where accuracy is important — such as the pharmaceutical industry — this accuracy can be indispensable.
