Weighing Machines

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Weighing machines are defined as mechanical or electro-mechanical devices for weighing or evaluating the mass of objects. There are a multitude of many different types of weighing machines. The broadest categories are usually classified as equal arm balances, unequal arm balances, spring balances and electronic scales. The first three categories have been used for many years, but the electronic scales have become almost universally used within the past ten years.

Equal Arm Balances: An equal armed balance is a basic balance which weighs objects by comparing them to other objects. This is achieved by placing the objects to be compared on a plate or pan that is connected to the scale. There are two plates or pans connected to the center of the scale by balance arm beams. These pans are equidistant. Proper use of this type of scale is very simple. To use an equal arm balance, first establish that the riders are equally distant and that the scale reads zero when nothing is placed on it. Then, place the two objects to be compared on the separate plates. If both plates are level with each other, the objects weight the same ...
... amount. If one side is closer to the ground, the heavier object rests on that plate.

Unequal Arm Balances: This type of scale is typically used for weighing smaller loads and was frequently used in laboratory settings. It has one beam that has two arms which vary in length †loads are placed in the pan that is suspended from the shorter arm and the longer arm on the beam has weights which slide across it to find a balance.

Spring Balances: This simple type of weighing machine is comprised of a spring on one end of the apparatus and a hook attached to an object on the other end. A spring scale meant to weigh small amounts usually has a less firm spring than those which are used to measure heavier weights. This scale works using the principle of Hooke s Law. This law says that the force required to lengthen a spring is directly proportional to the amount of space that spring is extended from the rest position. Therefore, these scales’ results can be somewhat approximate, so they are not often used when accuracy is crucial. Another drawback to weighing with spring balances is that the spring can permanently stretch over time.

Electronic Scales: These modern weighing machines use one or more load sensors to convert weight to an electronic signal. This signal is processed by electronic components to convert it into a digital value. The value is shown on an electronic display. Electronic scales have many advantages. They are much more precise than mechanical weighing machines. They are generally also more rugged and reliable, and will provide longer service life with less maintenance. The digital display is much easier to read, eliminating operator error. Furthermore, the weight results may be electronically sent to other devices, such as printers, data loggers, computers and other process equipment. The load sensors are the most critical part of an electronic scale. Stainless steel is the ideal material for these devices. Depending on the capacity required, scales are available in a number of different formats. These include laboratory scales for very small loads, bench scales, platform scales and floor scales, for increasing loads.