Hydraulic scales use compressed hydraulic fluid to measure the mass of a test weight, with load cells and a display translating the pressure into a visible indication. They range from simple overhead scales to large weighbridge models and are reliable and accurate, making them popular for high-traffic applications.
A hydraulic scale is a measuring device that uses the compression of hydraulic fluid by a test weight to indicate the mass of the test weight. This is typically accomplished by causing the trial weight to depress a piston or diaphragm which, in turn, compresses the fluid. The pressurized fluid is then fed to a Bourdon tube type analog meter or electronic sensor and display. In either case, the system is calibrated so that the displayed value indicates the mass value of the test weight. Hydraulic scales range in complexity from simple single piston overhead scales to large weighbridge models with multiple load cells.
Fluids act in predictable ways when compressed; each type of fluid has specific and known characteristics when placed under compression. This allows very accurate measurement of mass in hydraulic scale applications. All types of hydraulic scales consist of one or more load cells and a means of translating the resulting pressure into a visible mass indication. A load cell is typically little more than a piston or diaphragm with a small oil-filled compression chamber. When the trial weight rests on the piston, it moves downward and compresses the oil relative to the size of the trial weight.
This pressurized oil is used to indicate the mass of the test weight. This indication can be displayed in a number of ways, the simplest of which is the Bourdon tube meter. This gauge is typically used on small, single load cell scales and consists of a flat C-shaped tube connected via a series of links to an analog dial. When the oil pressure in the tube increases, it flexes and moves the gauge needle to indicate mass.
On larger scales, a load receptor or platform is situated on top of an array of hydrostatic cells. When a load is placed on the platform, it depresses all cells evenly. All hydraulic input lines from the load cells come together in a summing totalizer. This device is usually located away from the charging pad and consists of a series of receiver cells that translate incoming pressure into an electronic signal. This signal is passed to a processor that displays the mass of the charge on a digital display.
This type of hydraulic scale is generally used in weighbridge installations that measure the mass of large trucks or railway rolling stock. The cargo platforms used on these scales can measure up to 120 feet (37 meters) in length. Scales of this type are generally capable of accurately measuring loads of 120 tons or more. In addition to the hydraulic scale’s inherent accuracy, it also has very few moving parts and is reliable and easy to maintain, making it a popular choice for high-traffic applications.
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