The 181 Current Sensitive Preamplifier is normally used with any PAR lock-in to form a sensitive system optimized for measuring low-level currents such as those encountered in photometry and semiconductor research. Resulting system offers lower internal noise, greater frequency response, higher dynamic range, greater phase accuracy and lower input impedance than nearly any other low-level ac current-measuring system Overall system current sensitivity when operating with a lock-in is equal to the lock-in sensitivity multiplied by the 181 A/V sensitivity setting, which can be 10E-04 to 10E-09 Output attenuator provides 10:1 attenuation of output voltage Overload protection