Mechanical scales Weighing scale

a spring scale measures mass reporting distance spring deflects under load. contrasts balance, compares torque on arm due sample weight torque on arm due standard reference mass using horizontal lever. spring scales measure force, tension force of constraint acting on object, opposing local force of gravity. calibrated measured force translates mass @ earth s gravity. object weighed can hung spring or set on pivot , bearing platform.

in spring scale, spring either stretches (as in hanging scale in produce department of grocery store) or compresses (as in simple bathroom scale). hooke s law, every spring has proportionality constant relates how hard pulled how far stretches. weighing scales use spring known spring constant (see hooke s law) , measure displacement of spring variety of mechanisms produce estimate of gravitational force applied object. rack , pinion mechanisms used convert linear spring motion dial reading.

spring scales have 2 sources of error balances not: measured mass varies strength of local gravitational force (by as 0.5% @ different locations on earth), , elasticity of measurement spring can vary temperature. proper manufacturing , setup, however, spring scales can rated legal commerce. remove temperature error, commerce-legal spring scale must either have temperature-compensated springs or used @ constant temperature. eliminate effect of gravity variations, commerce-legal spring scale must calibrated used.

hydraulic or pneumatic scale

it common in high-capacity applications such crane scales use hydraulic force sense mass. test force applied piston or diaphragm , transmitted through hydraulic lines dial indicator based on bourdon tube or electronic sensor.