The dead weight machine

By employing a special case of Newton's Second Law of Motion, i.e. by subjecting a mass to acceleration due to the gravitational field of the earth, we can obtain a standard for the quantity of force. The accuracy of this standard depends on the precision with which the mass and the acceleration due to gravity can be measured.

In practice, we need to have standards available over a range of forces, and this has been done by designing what are known as 'dead weight machines', one of which is at SP in Borås. Using ingenious mechanical mechanisms, our machine can generate accurate forces over the range 250 – 1000000 N.

In the range up to 100 kN, the machine employs the direct force generated by the mass, while for higher forces up to 1 MN, the force is generated by a mechanical system of levers that magnifies the direct force by a factor of ten. In the lower measurement range, the relative error of the force is 0,005 %, while in the higher range it is 0,01 %. Relative repeatability and reversibility of the force generated by the machine are in the range 0,002 – 0,005 %.

The dead weight machine is installed in a temperature-controlled area, in which the ambient temperature is maintained constant at +20 °C.

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