Ajax Update Panel in Master Page

Hi,
  I have updatepanel in Master Page.There I add Timer for refereshing the panel for particular time interval.In Content Page I include one update panel with Modal popup extender.The problem is,When i run application the update panel in content page also refreshes as the update panel in master page refreshes.I want the update panel in content page,can't be refreshes based on update panel in Master page.How i solve this?can anyone help me to do this?