Modern digital scales rely on load cells to measure an object's weight. Before the use of load cells became widespread, a scale could be called digital if it simply had a digital readout. Older digital scales employed either a balance beam, in which the weight of an object was balanced against known units of weight until they balanced, or a spring that was depressed under the weight of the object and triggered a mechanical indicator to display the object's weight.
Digital Scale Components
Load cells are also known as force transducers. The load cells in a digital scale convert the force of an object's weight to an electrical signal. Load cells are typically composed of a strain gauge, which measures the strain of the object, and a load cell sensor. The strain gauge may be made of metal tracks or foil that is bonded to a circuit board. The sensor is the part of the cell that converts the object's force into the electrical signal, which the scale then displays on a digital readout.
How the Components Work Together
The tray of a digital scale adjusts to the weight of an object resting on it and distributes that object's weight evenly. The force of the object's weight bends the load cell beneath it. The object's weight also bends or deforms the strain gauge, flexing or stretching the gauge's backing, or compressing an enclosed liquid or gas within the cell. The scale uses this compression or deformation as an indicator of the object's weight. The signal created by this change then passes through a processor, which interprets it as a measure of weight, and the weight is displayed on the scale's digital display screen.
Types of Load Cells
There are three common types of load cells in digital scales. Hydraulic load cells employ an enclosed liquid. When you apply weight to the scale, the pressure of the liquid within increases, and the scale calculates your weight by measuring this change in pressure. Pneumatic load cells employ a similar principle but contain air instead of a liquid. The third type of load cell, the strain gauge load cell, employs a solid beam that flexes or bends under weight. Its deformation affects its electrical resistance, and the scale then measures this change to calculate your weight.
Smart Scales
Newer technologies allow the integration of previously unavailable features in digital scales. For example, a digital scale can also give an estimated measure of your body fat when you step onto it. It does this by sending a very minor electrical current into your foot, which then travels through one leg and back to the scale via your other leg. The ratio of fat to muscle is determined based on different levels of electrical resistance. Scales can also be Wi-Fi enabled and programmed to send your weight measurements to a website on the Internet. A Wi-Fi scale may share your weight with a remote party, such as your trainer at a weight loss program, or it may broadcast your weight loss on a social media network so that your online friends can see your progress and encourage you.
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