The 5381 Current Sensitive Amplifier is a high gain current to voltage converter which simplifies the measurement of low level ac currents, such as those encountered in photometric and capacitance measurement applications. When plugged into the 5301A Lock-In Amplifier, the system reads out in appropriate current units. Full scale sensitivity from 0.0001 A/V to 0.000000001 A/V in decade steps times the selected sensitivity at the 5301A Lock-In Mainframe.