How do reload a php or xml-file after 30 seconds automatical?

How do reload a php or xml-file after 30 seconds automatical?

Hello,

can I help me everywhere? How to reload a php or xml-file permenent on 30 seconds in jQuery?
I wrote a little javascript-script with the follow structure:

var ticker = {
    timer1: ' ',
    updateContent:function(php or xml-filename) {
        frequency = 30;
        var output = "php or xml-content";
         document.getElementById("insert").innerHTML = output;
    }
}

The php-file for the 30sec-reload-content is here:

echo "<span id='insert'></span>";