With the introduction of the ISO120 and ISO121, Burr- Brown also introduced partial discharge testing of analog isolation components. We have received several requests for an explanation of the test, what it provides for us and our customers, and how it relates to the more traditional test for isolation voltage ratings. What follows is information about the older test method and what it accomplished, partial discharge, how we test for it, and a comparison of similar products tested using the different methods. Some of this material appears in the ISO120/121 PDS, but bears repeating to give you the whole story.