LaTeX Forum

\documentclass[tikz, border=5pt]{standalone}
\usetikzlibrary{arrows.meta}

\tikzset{font=\sffamily}

\begin{document}
\begin{tikzpicture}[
	>/.tip=Stealth,
	thick,
	auto,
	box/.style={
		draw,
		minimum width=3em,
		minimum height=2em
	}
]
%	\draw[help lines] (-4,-2) grid (6,2);
	\draw[double distance=3pt] (-0.2,0) -- (0.2,0);
	\node[box] (PI) at (-2,0) {PI};
	\node[box] (P) at (3,1) {P};
	\node[box] (I) at (3,-1) {I};
	\node[draw, circle] (0) at (4.5,0) {};
	\draw[->] (-4,0) -- node {$e(t)$} (PI);
	\draw[->] (PI) -- node {$y(t)$} (-0.5,0);
	\draw[->] (0.5,0) -- node {$e(t)$} (1.5,0);
	\draw (P) -- +(-1.5,0) |- (I);
	\draw[->] (P) -| (0);
	\draw[->] (I) -| (0);
	\draw[->] (0) -- node {$y(t)$} +(1.5,0);
\end{tikzpicture}
\end{document}

\documentclass[11pt,a4paper,ngerman]{article}
\usepackage[T1]{fontenc}
\usepackage{selinput}
\SelectInputMappings{
  adieresis={ä},
  germandbls={ß}
}
\usepackage{babel}

\usepackage{tikz}

\usepackage{lmodern}
\usepackage{microtype}

\begin{document}
  \begin{tikzpicture}[>=stealth,thick]
%    \draw[help lines] (-4,-2) grid (6,2);
    \draw[double,double distance=3pt] (-0.2,0) -- (0.2,0);
    \node[draw,minimum width=3em,minimum height=2em] (PI) at (-2,0) {PI};
    \node[draw,minimum width=3em,minimum height=2em] (P) at (3,1) {P};
    \node[draw,minimum width=3em,minimum height=2em] (I) at (3,-1) {I};
    \node[draw,circle] (0) at (4.5,0) {};
    \draw[->] (-4,0) -- (PI) node[midway,above] {$e(t)$};
    \draw[->] (PI) -- (-0.5,0) node[midway,above] {$y(t)$};
    \draw[->] (0.5,0) --(1.5,0) node[midway,above] {$e(t)$};
    \draw (P) -- +(-1.5,0) |- (I);
    \draw[->] (P) -| (0);
    \draw[->] (I) -| (0);
    \draw[->] (0) -- +(1.5,0) node [midway,above] {$y(t)$};
 \end{tikzpicture}
\end{document}