Defining control parameters for charts globally in knitr

To control the size of the graph in knitr

I use the following code

\begin{figure}[H]
   \centering
<< label = Plot1, fig.width=5, fig.height=5, out.width=.7\linewidth, fig.keep = all>>=
...
@
    \caption{Plot}
    \label{fig:figPlot1}
\end{figure}

      

        
        
        
      

    

I wonder how to define these control parameters for charts globally instead of defining each chart. Thanks for your help and time.