▁such ▁as ▁ambient ▁temperature ▁and ▁hum id ity ▁for ▁the ▁respective ▁measurement ▁are ▁stored ▁in ▁the ▁program ▁and ▁included ▁in ▁the ▁Ki X act ▁calculation . ▁ ▁In vention ▁of ▁the ▁charge - to - vol t age ▁converter ▁ ▁In ▁ 1 9 4 8 , ▁Walter ▁P . ▁K ist ler ▁ ▁made ▁a ▁technical ▁break through ▁with ▁the ▁in vention ▁of ▁a ▁special ▁charge ▁ampl ifier ▁ ▁( charge - to - vol t age ▁converter ) ▁that ▁facil itated ▁the ▁broad ▁industrial ▁use ▁of ▁pie zo elect ric ity ▁ ▁and ▁was ▁pat ented ▁in ▁ 1 9 5 0 . ▁It ▁converts ▁the ▁extremely ▁small ▁charge ▁of ▁a ▁pie zo elect ric ▁sensor ▁ ▁to ▁a ▁proportional ▁elect rical ▁voltage . ▁ ▁Pie zo Star ▁cry st als ▁ ▁Since ▁ 1 9 9 8 , ▁the ▁K ist ler ▁Group ▁has ▁been ▁growing ▁its ▁own ▁cry st als ▁for ▁use ▁in ▁pie zo elect ric ▁sens ors . ▁The ▁development ▁of ▁new ▁cry stal ▁comp ounds ▁was ▁necessary ▁due ▁to ▁rising ▁dem ands ▁on ▁sens itivity , ▁size ▁( in cre asing ▁mini atur ization ▁of ▁the ▁sens ors ) ▁and ▁higher ▁operating ▁temper atures . ▁Pie zo Star ▁cry st als ▁are ▁character ized ▁by ▁a ▁high ▁pie zo elect ric ▁sens itivity , ▁low - temper ature ▁dependence , ▁high ▁stability ▁of ▁their ▁properties ▁and ▁operating ▁temper atures ▁in ▁excess ▁of ▁ 6 0 0   ° C . ▁No ▁phase ▁transition ▁occurs ▁up ▁to