Calibrating device for load cells

A fluid operated calibrating device for a load cell, said device including;

• substantially vertical spaced-apart first and second chambers for containing the fluid having respective upwardly facing open ends, said first chamber having a cross-sectional area A.sub.P transverse to the vertical direction thereof and said second chamber having a cross-sectional area A.sub.R transverse to the vertical direction thereof that is greater than area A.sub.P,
• a third chamber providing fluid communication between the first and second chambers,
• a plunger member having a weight W.sub.p disposed above the first chamber, said member operable to move in opposite vertical directions relative the first chamber and having a side thereof facing upwardly from the open end of the first chamber that is adapted to receive standardized deadweights W.sub.(1, 2, . . . n),
• a ram member having a weight W.sub.r disposed above the second chamber, said member operable to move in opposite vertical directions relative the second chamber and having a side thereof facing upwardly from the open end of the second chamber adapted to apply a force F to the load cell,
• a first flexible seal extending between the plunger member and a wall surrounding the first chamber, said seal operable to create a resistance S.sub.p in response to movement of the plunger member whilst providing a fluid tight seal for containing the fluid within the first chamber,
• a second flexible seal extending between the ram member and a wall surrounding the second chamber, said seal operable to create a resistance Sr in response to movement of the ram member whilst providing a fluid tight seal for containing the fluid within the second chamber,
• said device operable such that when deadweights W.sub.(1, 2, . . . n) are placed upon the plunger member surface, the plunger member moves downwardly to pressurize the fluid within the first, second and third chambers and cause the ram member to move upwardly such that force F is defined by the equation:
• F=(A.sub.R /A.sub.P)(W.sub.1, 2 . . . n +W.sub.P -S.sub.P)-W.sub.R -S.sub.R.