jQuery ajax xml help

jQuery ajax xml help

Hi, I need a way that a xml file needs to retrived from the server in s ynchronous way 

$(document).ready(function(){

var x=$.ajax({
      type: "GET",
      url: "status.xml",
      cache: false,
      async: false,
      dataType: "xml",
      complete: function() {
 
          $(this).addClass("done");
                                    }
 });

            if(x.done) {
                               // process the xml
                           }

});

I´ve set it to async: false so why it does not keep updating the xml file? The xml file is requested only one time than it stops.
How can I keep it running all the time, this data on xml are from sensors and need to be updated has fast has the server can reply the status.xml 

Regards