Agilent 33120A User's Guide

Chapter 7 TutorialFloating Signal GeneratorsFloating Signal GeneratorsMany applications require a test signal which is isolated from earthground for connection to powered circuits, to avoid ground loops, or tominimize other common mode noise. A floating signal generator such asthe 33120A has both sides of the output BNC connector isolated fromchassis (earth) ground. As shown in the figure below, any voltagedifference between the two ground reference points (Vground) causes acurrent to flow through the function generator’s output common lead.This can cause errors such as noise and offset voltage (usually powerlinefrequency related), which are added to the output voltage.The best way to eliminate ground loops is to maintain the functiongenerator’s isolation from earth ground. The function generator’sisolation impedance will be reduced as the frequency of the Vgroundsource increases due to low-to-earth capacitance Cle (approximately4000 pF for the 33120A). If the function generator must beearth-referenced, be sure to connect it (and the load) to the samecommon ground point. This will reduce or eliminate the voltagedifference between devices. Also, make sure the function generator andload are connected to the same electrical outlet if possible.R L50 WLoadVgenR LCommonVgroundC leR i >10 GWR L = Lead Resistance282