[Tex/LaTex] Drawing a block diagram with TiKz

Question

I need some help drawing a block diagram using TiKz.

I want draw something similar to this:

However, I'm struggling to go further than this so far:

using the code below:

\documentclass{standalone}

\usepackage{tikz}       
\usetikzlibrary{arrows,positioning,patterns,decorations.pathmorphing}

\begin{document}

\tikzstyle{block} = [draw, rectangle, minimum size=5em]
\tikzstyle{joint} = [draw, circle, minimum size=1em]

\begin{tikzpicture}[>=stealth, auto, node distance=2cm]
    % Place nodes
    \node [block] (system) {System};
    \node [coordinate, left=of system] (infork) {};
    \node [coordinate, left=of infork] (input) {};
    \node [coordinate, right=of system] (outfork) {};
    \node [coordinate, right=of outfork] (output) {};
    \node [coordinate, above=of system] (disturbances) {};
    \node [block, below=of system] (model) {Model};
    \node [joint, right=of model] (sum) {};
    \node [coordinate, right=of sum] (error) {};
    % Connect nodes
    \draw [->, decorate, decoration={snake, post length=1mm}] (disturbances) -- node {\(d'\)} (system);
    \draw [->] (input) -- node {\(u'\)} (system);
    \draw [->] (system) -- node {\(t'\)} (output);
    \draw [->] (model) -- node {\(y\)} (sum);
    \draw [->] (sum) -- node {\(\epsilon\)} (error);
    \draw [->] (infork) |- node {\(u\)} (model);
    \draw [->] (outfork) -- node {\(t\)} (sum);
\end{tikzpicture}

\end{document}

Namely, I would like to find how to:

• Place a the rectangle called Measurement between the two blocks. Preferably, this rectangle would be filled with light gray color and would be bordered by a dashed line. Note: I don't mind the rectangle cover the vertical lines. I just want these to keep its vertical direction

• Place the sum circle exactly behind the fork so as to have a vertical line connecting t' to this circle

• Have the u and t placed correctly (e.g. like they are in the first picture)

• Have the +and - signs where the arrows meet the circle

Answer 1

Is this what you were looking for?

Fixes:

1. Added a node Measurement positioning it halfway between the nodes System and Model using this syntax: \node ... at ($(system)!.5!(model)$) {};. This requires calc to be added to the Tikz libraries.
2. Changed your diagonal path to \draw [->] (outfork) -| (sum.north) node [very near end] {\(t\)}; so that the node stops exactly at the north point of sum.
3. The [very near end] above ensures that the node appears very close to the arrow tip.
4. Removed minimal size for your nodes that makes them look square (it's a bit ugly), and replaced it with inner sep which adds space inside the node consistently so that the rectangle borders are equally far from the node text.
5. For the node u (the path on the left), I added the key [anchor=south west] so that it moves it right and up a bit and appears next to the path.
6. Used labels for the - and + symbols. Originally they were nodes but it looks better like this and the code is cleaner and shorter.

\documentclass{standalone}

\usepackage{tikz}       
\usetikzlibrary{arrows,positioning,patterns,decorations.pathmorphing,calc}

\begin{document}

\tikzstyle{block} = [draw, rectangle, inner sep=6pt]
\tikzstyle{joint} = [draw, circle,minimum size=1em]

\begin{tikzpicture}[>=stealth, auto, node distance=2cm]
    % Place nodes
    \node [block] (system) {System};
    \node [coordinate, left=of system] (infork) {};
    \node [coordinate, left=of infork] (input) {};
    \node [coordinate, right=of system] (outfork) {};
    \node [coordinate, right=of outfork] (output) {};
    \node [coordinate, above=of system] (disturbances) {};
    \node [block, below=of system] (model) {Model};
    \node [joint, right=of model, anchor=center,label={[shift={(2mm,-1mm)}]-},label={[shift={(-3mm,-5.5mm)}]\tiny +}] (sum) {};

    \node [coordinate, right=of sum] (error) {};
    \node [block, dashed, fill=gray, anchor=center, text width=7cm, align=center] at ($(system)!.5!(model)$) {\textsc{Measurement}};

    % Connect nodes
    \draw [->, decorate, decoration={snake, post length=1mm}] (disturbances) -- node {\(d'\)} (system);
    \draw [->] (input) -- node {\(u'\)} (system);
    \draw [->] (system) -- node {\(t'\)} (output);
    \draw [->] (model) -- node {\(y\)} (sum);
    \draw [->] (sum) -- node {\(\epsilon\)} (error);
    \draw [->] (infork) |- node [anchor=south west] {\(u\)} (model);
    \draw [->] (outfork) -| (sum.north) node [very near end] {\(t\)};
\end{tikzpicture}

\end{document}