Spring scale
The spring scale (also bag balance) and the spring force knives are instruments that use the stretching of a coil spring to measure a force. The spring scale determined by the weight of the mass and has a scale in kilograms ( kg). The scale of the spring force of the blade is expressed in Newtons (N).
The principle
The spring scale uses to measure train or weight forces the linear and elastic stretching of a coil spring when stretched. The length of expansion is measured according to the Hooke's law is proportional to the tensile force in the linear expansion area of the spring. For practical use, a coil spring is provided at the ends each with a suspension or securing device, and the spring travel along with a scale and a pointer.
There are also high-quality bench scales with a large circle phasor measurement head for use in industry, trade and laboratories, which work on the spring balances principle. This is i.d.R. to to solid devices in heavy metal housings with large displays behind glass. The usual weighing ranges and graduations are 25 kg / 50 g, 50 kg / 100 g and 100 kg / 200 g, with mostly an estimated reading between the scale divisions is still possible and sufficiently accurate. These scales are built (2011), only a few producers today. They found wide use in post offices / branches, large kitchens, workshops and laboratories and have been or are valued for their easy handling (where the weight scales sliding weights have to be operated, electronic scales must be switched on and off again ).
As a " suitable " for the respective measurement purpose, a spring, on the one hand on the area of their reversible strain effect of a force on the scale required permits and on the other along the intended suspension travel has a linear relationship between force and displacement, ie can be characterized by a spring constant.
A body suspended from the lower end of a suspended spring balance, the spring is stretched under the action of gravity and the force of gravity, or - for the light of the local factors in scale - displayed the mass of the body.
When determining the mass with a spring balance is to be noted that the size of the gravitational acceleration is different locally both by geographical and topographical situation after ( hence the term local factor). A at 45 ° latitude calibrated weight spring balance shows, for example, at the equator to 0.26% too little, near the poles but by 0.26 % too much. On the moon, the corresponding indicator value would be only one-sixth of that on Earth. This effect have not scales with counterweights on the other hand only spring balances for gravity determinations are suitable.
Measurement accuracy
The accuracy of simple tubular models is usually not large; it is negatively affected by structural characteristics (friction, clamping of the spring in the housing ) to coarse or too small scale division and unfavorable readability (small numbers ). Better read are hanging scales with round dial instrument. The above great bench scales are the particularly high-quality design is and the manufacturer usually given with an accuracy of 0.2 % of full scale value to show under careful handling and regular maintenance but practical accuracy of 0.1 % of full scale value. Your accuracy and ease of use is compared to the simple models favored by more complex processing, higher-quality materials, careful adjustment as well as supported in Carbide cutting LAM and vibration damping ( oil dampers ).
Dynamometer for Engineering and Physics
See main article force measurement.
- The gravimeter is a precision " spring balance " ( oblique bars) of Geophysics and Geodesy. This is the earth's gravitational field is determined ( from 9.5 to 9.9 ± 10-8 m / s ²).
- Ring dynamometer for measuring mechanical train and compressive forces
- Torsion balance ( torsion ) for determining the gravitational constant (1798 )