ClearAll[L,c]
ω=314;
nHarm=5;
Q=10;
R=1.5;
L=L/.Solve[Q==((ω*L)/R)][[1]];
c=c/.Solve[(1/(Sqrt[L*c]))==nHarm*ω][[1]];

ClearAll[uz];
SeedRandom[1]
uz[t_]=1Sin[ω*t+Random[]]+0.05*Sin[5*ω*t+Random[]]+0.01Sin[7*ω*t+Random[]];
rceSoucastek={uR[t]==iR[t]*R,uL[t]==L*iL'[t],ic[t]==c*uc'[t]};
rceNapeti={0==uz[t]-uR[t]-uL[t]-uc[t]};
rceProudy={iR[t]==iL[t],iL[t]==ic[t]};
rcePocatecnichPodminek={uc[0]==0,iL[0]==0};
tmax=0.02;
res=NDSolve[Union[rceNapeti,rcePocatecnichPodminek,rceProudy,rceSoucastek],{uR,ic,uc,iL,iR,uL},{t,0,tmax}][[1]];
Plot[{iL[t]/.res,0.01uz[t]},{t,0,tmax}];

ClearAll[cv]
n=1000;
io=5;
Δt=(tmax/(n-1));
datUz=Table[{t,uz[t]},{t,0,tmax,Δt}];
datI=Table[{t,iL[t]/.res},{t,0,tmax,Δt}];
fceUz=Interpolation[datUz,InterpolationOrder->io];
fceI=Interpolation[datI,InterpolationOrder->io];
data=Table[{fceI''[t],fceI'[t],fceI[t],fceUz'[t]},{t,0,tmax,Δt}];
proklad=Fit[data,{d2i,d1i,i},{d2i,d1i,i}];
Lv=Coefficient[proklad,d2i];
Rv=Coefficient[proklad,d1i];
jednaKuc=Coefficient[proklad,i];
cv=cv/.Solve[(1/cv)==jednaKuc][[1]];
Print["δR= ",100((R-Rv)/R),"  δL= ",100((L-Lv)/L),"  δc= ",100((c-cv)/c),"  %"]

(*dodat sum a jeho filtrace*)