<script>
function reloadIt()
{
frm=document.getElementsByName("grafiek")[0];
frm.src=frm.src;
setTimeout("reloadIt()",600000); // 10 mins
}
setTimeout("reloadIt()",60000); // Init : 1 minute
</script>
<iframe name="grafiek" src="http://www.site.com/path/" width="1200px" height="800px" frameborder="0" scrolling="no"></iframe>