GENERAL. a. The Keithley Model 414A is a completely solid-state picoammeter which measures currents over 17 ranges from 10⁻² to 10⁻¹⁰ ampere full scale. Accuracy is ±2% of full scale on the 10⁻² to 10⁻⁸ ampere ranges and ±4% of full scale on the 3 x 10⁻⁹ to 10⁻¹⁰ ampere ranges. b. The Picoammeter employs matched MOSFET transistors in the input followed by a differential amplifier stage, a transistor driver and a transistor output stage. Negative feedback is used for stability and accuracy. FEATURES. b. A unique circuit provides complete overload protection for Model 414A without compromising the outstanding features of the MOSFET input. The Picoammeter 'Will withstand transient overloads up to 1000 volts without damage, and overload recovery is almost instantaneous. a. The time and temperature stability of the 414A Picoammeter is unmatched by any other inexpensive picoammeter. The Model 414A will operate for days without requiring rezeroing. Zero drift with time is less than 0.5% of full scale per week. Temperature drift is equally small — a change of 10°C affects the reading less than 0.5% of full scale on the most sensitive range. c. Fast warm-up is an inherent characteristic of the Picoammeter. It can be used almost immediately on its most sensitive range. For maximum stability, however, about 10 minutes warm-up time should be allowed. d. One volt or 1 milliampere at full-scale deflection on all ranges is provided to drive chart recorders. The 1 milliampere recorder output will drive the Keithley 370 Recorder directly. When potentiometric recorders are used, the output voltage can be conveniently divided by a shunt resistor and adjusted for full scale with the rear panel Calibration potentiometer.