function  [T,Td] = kaifang_ceiling(sigma,freedom,P_fa)

%*********************************
% ** %檢測門限計算
% ** sigma均方根誤差;freedom自由度;P_fa虛警概率
% **********************************

T = chi2inv((1-P_fa),freedom)*sigma*sigma;
Td = sqrt(T/freedom);
% H_ceiling = [2.38,2.28,2.214,2.163,2.122,2.086,2.055,2.027];%
% arp = Td*H_ceiling(freedom)*sqrt(freedom);