A primary standard is a pressure reference instrument known for its high accuracy, in which its functionality is based on the formula of pressure = force/area (P=F/A). It is also referred to as a deadweight tester, primary pressure standard or pressure balance.
In a deadweight tester, the force is supplied by a mass in a gravitational field on top of a piston with a specific cross-sectional area that rotates within a cylinder. This piston cylinder system is manufactured to very tight tolerances for smooth, precision operation. The fluid (pneumatic or hydraulic) under the piston is pressurized so the piston and mass “float” in equilibrium. The pressure in the fluid is equal to the force exerted by the mass over the cross sectional area of the piston.
A digital deadweight tester calibrates pressure gauges , through hydrostatic pressure created by fluid. Through piston gauge technology, the fluid is able to transmit the pressure.