What is the best approach for refreshing the page content/values after 3 seconds?

Please suggest some approach I have a device from which I am getting reading in the form of measurement like volt, amp, watt, etc so I have a dashboard.jsp page where I have to refresh the readings every 3 seconds and the device will be attached on network. So, threading is a good approach or ajax calls as some folks telling threading in a web applications make the loading slower and crash the application. I am confused please post your ideas and explain if possible.