The Keithley Models 416 and 417 High-Speed Picoammeters
measure currents over 18 ranges from 10⁻¹³ to 3 x 10⁻⁵
ampere full scale. The rise time of, the instruments is 30
milliseconds on the 10⁻¹² ampere range with no external
capacitance across the input. Accuracy is * 2% of full scale
from 3 x 10⁻⁵ to 10⁻⁸ ampere, and +/- 3% of full scale on
the other ranges. Zero drift is less than 1% per eight hours.
b. The Picoammeters use an electrometer tube input with
solid-state amplifiers and power supply. The amplifier
circuit is completely contained in the Models 4160 and 4170
Input Heads, which can be removed from the main chassis and
operated remotely up to distances of 25 feet. The full
capabilities of the high-speed circuitry are realized,
therefore, by minimizing external capacitance and noise
usually introduced by long cable runs to the input.
a. Variable damping increases the rise time approximately
three seconds to facilitate measurements of steady currents
without: disturbances due to 60 cps pickup or noise.
b. Three volts at full-scale deflection on all ranges is
provided at up to one milliampere to drive chart recorders
c. A zero check switch permits zeroing the meter without
disturbing the circuit.
1-3. DIFFERENCES BETWEEN THE MODELS 416 AND 417.
a. The Picoammeter circuits in the two models are the same.
The Model 417, however, provides a suppression current at
the input up to 1000 times full scale on most ranges. This
permits full-scale display of 0.1% variations of a signal or
suppression of a steady background signal.
b. The instructions in this Manual are for both models,
except those paragraphs concerning the suppression current
operation and circuit. These instructions are identified as
applying only to the Model 417. Separate schematic diagrams
are contained in the Manual for each instrument.