How Does a Deadweight Tester Work?

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How does a deadweight tester work?
 
A deadweight tester generates pressure by exerting a force (F) over an area (A), which is also the definition of pressure (P) :

P = F/A

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. 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 cross sectional area of the piston.
 
This is a very simple and straightforward conceptual explanation, however in practice, the force and the cross sectional area of the piston are affected by environmental conditions.
 
The force is affected by local gravity and buoyancy created by the surrounding atmosphere. The area of the piston is affected by the temperature of and the pressure surrounding the piston.
 
An equation that takes all of these influences into account is used to calculate the actual pressure generated by the deadweight tester.
 
Manufacturers of deadweight testers will usually have an automated way to make these corrections and determine the mass to generate a given pressure.  The WIKA CPU6000 (formerly the CPU5000) can calculate the mass required to generate any pressure, sense the environmental conditions and factor them into the equation to calculate the pressure.

The video below shows a graphical explanation: