▁ ▁Princi ple ▁of ▁operation ▁The ▁sens ing ▁element ▁of ▁a ▁P IG A ▁is ▁a ▁p end ul ous ▁mass , ▁free ▁to ▁pivot ▁by ▁being ▁mounted ▁on ▁a ▁bearing . ▁ ▁A ▁spin ning ▁gy ros cope ▁is ▁attached ▁such ▁that ▁it ▁would ▁rest rain ▁the ▁p end ul um ▁against ▁" fall ing " ▁in ▁the ▁direction ▁of ▁acceleration . ▁ ▁The ▁p end ul ous ▁mass ▁and ▁its ▁attached ▁gy ros cope ▁are ▁themselves ▁mounted ▁on ▁a ▁ped est al ▁that ▁can ▁be ▁rot ated ▁by ▁an ▁electric ▁tor que ▁motor . ▁ ▁The ▁rot ational ▁axis ▁of ▁this ▁ped est al ▁is ▁mut ually ▁orthogonal ▁to ▁the ▁spin ▁axis ▁of ▁the ▁gy ros cope ▁as ▁well ▁as ▁the ▁axis ▁that ▁the ▁p end ul um ▁is ▁free ▁to ▁move ▁in . ▁ ▁The ▁axis ▁of ▁rotation ▁of ▁this ▁ped est al ▁is ▁also ▁in ▁the ▁direction ▁of ▁the ▁measured ▁acceleration . ▁ ▁The ▁position ▁of ▁the ▁p end ul um ▁is ▁sens ed ▁by ▁precision ▁elect rical ▁contacts ▁or ▁by ▁optical ▁or ▁elect romagnet ic ▁means . ▁ ▁Should ▁acceleration ▁dis place ▁the ▁p end ul um ▁arm ▁from ▁its ▁null ▁position ▁the ▁sens ing ▁mechanism ▁will ▁operate ▁the ▁tor que ▁motor ▁and ▁rotate ▁the ▁ped est al ▁such ▁that ▁the ▁property ▁of ▁gy ro scop ic ▁pre cess ion ▁rest ores ▁the ▁p end ul um ▁to ▁its ▁null ▁position . ▁▁ ▁The ▁rate ▁of ▁rotation ▁of ▁the ▁ped est al ▁gives ▁the ▁acceleration ▁while ▁the ▁total