Balance scales Weighing scale

1 balance scales

1.1 mechanical balances

1.1.1 roberval balance


1.2 electronic devices

1.2.1 microbalance
1.2.2 analytical balance
1.2.3 pendulum balance scales


1.3 symbolism
1.4 history of balance scale

balance scales

finely crafted pan balance or scales boxed set of standardized gram masses.

the original form of balance consisted of beam fulcrum @ center. highest accuracy, fulcrum consist of sharp v-shaped pivot seated in shallower v-shaped bearing. determine mass of object, combination of reference masses hung on 1 end of beam while object of unknown mass hung on other end (see balance , steelyard balance). high precision work, such empirical chemistry, center beam balance still 1 of accurate technologies available, , commonly used calibrating test masses.

mechanical balances

the balance (also balance scale, beam balance , laboratory balance) first mass measuring instrument invented. in traditional form, consists of pivoted horizontal lever arms of equal length – beam – , weighing pan suspended each arm (hence plural name scales weighing instrument). unknown mass placed in 1 pan , standard masses added other pan until beam close equilibrium possible. in precision balances, more accurate determination of mass given position of sliding mass moved along graduated scale. technically, balance compares weight rather mass, but, in given gravitational field (such earth s gravity), weight of object proportional mass, standard masses used balances labeled in units of mass (e.g. g or kg).

two 10-decagram masses



market hawker weighing meat (in kati) on beam balance.



masses of 50, 20, 1, 2, 5 , 10 grams

unlike spring-based scales, balances used precision measurement of mass accuracy not affected variations in local gravitational field. (on earth, example, these can amount ±0.5% between locations.) change in strength of gravitational field caused moving balance not change measured mass, because moments of force on either side of beam affected equally. balance render accurate measurement of mass @ location experiencing constant gravity or acceleration.

very precise measurements achieved ensuring balance s fulcrum friction-free (a knife edge traditional solution), attaching pointer beam amplifies deviation balance position; , using lever principle, allows fractional masses applied movement of small mass along measuring arm of beam, described above. greatest accuracy, there needs allowance buoyancy in air, effect depends on densities of masses involved.

aluminum, mass-produced balance scale (steelyard balance) sold , used throughout china: scale can inverted , held larger ring beneath user s right hand produce greater leverage heavier loads (hainan province, china)

to reduce need large reference masses, off-center beam can used. balance off-center beam can accurate scale center beam, off-center beam requires special reference masses , cannot intrinsically checked accuracy swapping contents of pans center-beam balance can. reduce need small graduated reference masses, sliding weight called poise can installed can positioned along calibrated scale. poise adds further intricacies calibration procedure, since exact mass of poise must adjusted exact lever ratio of beam.

for greater convenience in placing large , awkward loads, platform can floated on cantilever beam system brings proportional force noseiron bearing; pulls on stilyard rod transmit reduced force conveniently sized beam.

one still sees design in portable beam balances of 500 kg capacity commonly used in harsh environments without electricity, in lighter duty mechanical bathroom scale (which uses spring scale, internally). additional pivots , bearings reduce accuracy , complicate calibration; float system must corrected corner errors before span corrected adjusting balance beam , poise.

a roberval balance. pivots of parallelogram understructure makes insensitive load positioning away center, improves accuracy, , ease of use.


roberval balance

in 1669 frenchman gilles personne de roberval presented new kind of balance scale french academy of sciences. scale consisted of pair of vertical columns separated pair of equal-length arms , pivoting in center of each arm central vertical column, creating parallelogram. side of each vertical column peg extended. amazement of observers, no matter roberval hung 2 equal weight along peg, scale still balanced. in sense, scale revolutionary: evolved more-commonly encountered form consisting of 2 pans placed on vertical column located above fulcrum , parallelogram below them. advantage of roberval design no matter equal weights placed in pans, scale still balance.

a gear balance: = axle, f = frame, g = generator, gl = geared linkage, wl = weighted lever; counter weight added balance, gear linkages free running on rotating frame

further developments have included gear balance in parallelogram replaced odd number of interlocking gears greater one, alternating gears of same size , central gear fixed stand , outside gears fixed pans, sprocket gear balance consisting of bicycle-type chain looped around odd number of sprockets central 1 fixed , outermost 2 free pivot , attached pan.

because has more moving joints add friction, roberval balance consistently less accurate traditional beam balance, many purposes compensated usability.

electronic devices
microbalance

a microbalance instrument capable of making precise measurements of mass of objects of relatively small mass: of order of million parts of gram.

analytical balance


mettler digital analytical balance 0.1 mg readability

an analytical balance class of balance designed measure small mass in sub-milligram range. measuring pan of analytical balance (0.1 mg or better) inside transparent enclosure doors dust not collect , air currents in room not affect balance s operation. enclosure called draft shield. use of mechanically vented balance safety enclosure, has uniquely designed acrylic airfoils, allows smooth turbulence-free airflow prevents balance fluctuation , measure of mass down 1 μg without fluctuations or loss of product. also, sample must @ room temperature prevent natural convection forming air currents inside enclosure causing error in reading. single-pan mechanical substitution balance maintains consistent response throughout useful capacity achieved maintaining constant load on balance beam, fulcrum, subtracting mass on same side of beam sample added.

electronic analytical scales measure force needed counter mass being measured rather using actual masses. such must have calibration adjustments made compensate gravitational differences. use electromagnet generate force counter sample being measured , outputs result measuring force needed achieve balance. such measurement device called electromagnetic force restoration sensor.

pendulum balance scales

pendulum type scales not use springs. design uses pendulums , operates balance , unaffected differences in gravity. example of application of design scales made toledo scale company.

symbolism

the ancient egyptian book of dead depicts scene in scribe s heart weighed against feather of truth.

the scales (specifically, two-pan, beam balance) 1 of traditional symbols of justice, wielded statues of lady justice. corresponds use in metaphor of matters being held in balance . has origins in ancient egypt.

scales symbol astrological sign libra.

history of balance scale

the balance scale such simple device usage far predates evidence. has allowed archaeologists link artifacts weighing scales stones determining absolute mass. balance scale used determine relative mass long before absolute mass.

the oldest evidence existence of weighing scales dates c. 2400–1800 b.c. in indus river valley (modern-day pakistan). prior that, no banking performed due lack of scales. uniform, polished stone cubes discovered in settlements used mass-setting stones in balance scales. although cubes bear no markings, masses multiples of common denominator. cubes made of many different kinds of stones varying densities. mass, not size or other characteristics, factor in sculpting these cubes.

in egypt, scales can traced around 1878 b.c., usage extends earlier. carved stones bearing marks denoting mass , egyptian hieroglyphic symbol gold have been discovered, suggests egyptian merchants had been using established system of mass measurement catalog gold shipments or gold mine yields. although no actual scales era have survived, many sets of weighing stones murals depicting use of balance scales suggest widespread usage. in china, earliest weighing balance excavated tomb of state of chu of chinese warring states period dating 3rd 4th century bc in mount zuojiagong near changsha, hunan. balance made of wood , used bronze masses.

variations on balance scale, including devices cheap , inaccurate bismar (unequal-armed scales), began see common usage c. 400 b.c. many small merchants , customers. plethora of scale varieties each boasting advantages , improvements on 1 appear throughout recorded history, such great inventors leonardo da vinci lending personal hand in development.

even advances in weighing scale design , development, scales until seventeenth century ad variations on balance scale.