The New International Encyclopædia/Weighing Machine
WEIGHING MACHINE. A contrivance for ascertaining the weight of objects. The most common form of weighing machine is the platform scale, in which a small known weight at one end of multiplying beams is made to balance a heavy unknown weight at the other end. The principle of the unequal beam balance is simply the principle of the lever (see Lever; Balance), and as applied to scales it may be illustrated by the accompanying diagram. Here we have the beam hinged at l and m and attached by a rod no to the scale beam oq. At jkrs is a U-shaped lever hinged to fixed pivots at j and k and to the lever lnm at r and s. If now we let the broken lines a, b, c, d represent a stiff platform, which is carried on the two levers by means of standards at e, f, g, and h, we have represented all the principal operating parts of the ordinary platform scale. To understand the mode of operation, assume that a load is placed upon the platform a, b, c, d. This load is conveyed to the system of levers by the standards e, f, g, and h, and depresses them so that they exert a pull downward on the rod no and the short arm of the lever op. This pull is balanced by sliding the weight w along the lever or scale beam oq, which is so graduated into pounds and fractions that the weight of the article on the platform is read at a glance. It is now plain that we have only to vary the number of levers and relative lengths of the arms of these levers to secure almost any multiplication of the weight that we please. In ordinary platform scales a weight w of 1 pound balances a load of 100 pounds on the platform. But this ratio is increased to 1 to 500 or to 1 to 1000 in scales for weighing loaded wagons and cars. The arrangement of levers shown in the accompanying diagram is a common one, but there are many others in use, each of which is adapted to some particular direction or use of the scale.
DIAGRAM OF PLATFORM SCALE.
Some scales work automatically, taking material from a large hopper, weighing out a certain amount and discharging it and then repeating the operation. Such contrivances are used for bagging sugar, coffee, etc., and for weighing out coal for sale. Scales are built which have a capacity for weighing very heavy loads; examples of these are railway car and locomotive scales, cattle scales with a capacity of weighing from 20 to 200 head of cattle, and grain scales of 500 bushels capacity and more. A scale designed for weighing heavy guns at the Watervliet Arsenal, Troy, N. Y., has a capacity for weighing 300,000 pounds on a platform 12 × 15 feet, or a capacity of nearly 1700 pounds per square foot. Besides scales operating on the principle of the balance, there are weighing machines which operate by compressing a coiled spring or by twisting a bar of metal. The spring scale is a very common device, and in the form of a dynamometer for registering the pull of locomotives is made with very large capacities. For the most part, however, spring scales are of small capacity. They are not as accurate as balance scales. See Spring Balance.