The first pressure measurements were made using columns of fluid, and the technique is still in use today. For example, a mercury column is commonly used in doctors’ surgeries to measure blood pressure. It has also historically been used in meteorology, with weather forecasts including expressions such as “the atmospheric pressure today is 712 millimetres of mercury” (meaning that the mercury column is 712mm high).
The dead weight pressure tester
However, at higher pressures fluid columns would be impractical due to their sheer size.
Therefore the columns are replaced by dead weights on top of a piston in a cylinder. A force K (generated by a ram) increases the pressure to the point where the weight is lifted and floats.
With a piston area of 1cm² and a mass of 1000kg, the floating condition occurs at a pressure of 100kg/cm², which equates to 98.1bar at 1g force (standard gravity).
Very accurate measurements of pressure can be realised this way.
Read more: Index to all of our Technical Notes on Pressure
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