documentclass[a4paper,10pt]{article}

usepackage{tikz}
usepackage{pgf}
usetikzlibrary{arrows, calc, decorations.pathmorphing, shapes}

pgfrealjobname{test}


begin{document}
    beginpgfgraphicnamed{levels}
    begin{tikzpicture}[scale=1, font=normalsize, every node/.append style={transform shape}]
        node[rectangle, draw, minimum width=1.5em, minimum height=1.5em, line width=0.05em] (n1) at (0,0) {1};
        node[rectangle, draw, minimum width=1.5em, minimum height=1.5em, line width=0.05em] (n2) at (2,0) {2};
    end{tikzpicture}
    endpgfgraphicnamed
end{document}

latex --jobname=levels test.tex
dvips -o levels.eps levels.dvi

documentclass[a4paper,10pt]{article}

usepackage{tikz}
usetikzlibrary{external}
tikzexternalize

usepackage{lipsum}

begin{document}%
lipsum[1]

begin{tikzpicture}[scale=1, font=normalsize, every node/.append style={transform shape}]
node[rectangle, draw, minimum width=1.5em, minimum height=1.5em, line width=0.05em] (n1) at (0,0) {1};
node[rectangle, draw, minimum width=1.5em, minimum height=1.5em, line width=0.05em] (n2) at (2,0) {2};
end{tikzpicture}

lipsum[2]
end{document}

pdflatex.exe --shell-escape -synctex=1 -interaction=nonstopmode %.tex

usetikzlibrary{external}

tikzset{external/system call={pdflatex tikzexternalcheckshellescape
                                        -halt-on-error
                                        -interaction=batchmode
                                        -jobname "image" "texsource"
                                        && pdftops -eps "image.pdf"}}
tikzexternalize[shell escape=-enable-write18]