428-112-04E Keithley Programmable Current Amplifier's Front Panel Board for 428-PROG

This Keithley Model 428-PROG Programmable Current Amplifier converts fast, small currents to a voltage, which can be easily digitized or displayed by an oscilloscope, waveform analyzer, or data acquisition system. It uses a sophisticated "feedback current" circuit to achieve both fast rise times and sub-picoamp noise. The gain of the Model 428-PROG is adjustable in decade increments from 103V/A to 1011V/A, with selectable rise times from 2μs to 300ms. The Model 428-PROG offers fast response at low current levels, which is unmatched by either electrometers or picoammeters. The nine current amplification ranges allow the greatest flexibility in making speed/noise tradeoffs. The Model 428-PROG can be used with any of Keithley's data acquisition boards to implement a very cost-effective, low current measurement system with wide bandwidth and fast response. The Model 428-PROG incorporates a second order Bessel-function filter that minimizes noise without increasing rise time on high-gain ranges. This can be defeated in situations where 6dB/ octave roll-off is desired, as in control loops of scanning tunneling electron microscopes. Input and output connections to the Model 428-PROG are made with BNC connectors. INPUT HI is connected to a programmable ±5V supply, which permits suitable bias voltages to be applied to devices-under-test or current collectors. This eliminates the need for a separate bias supply. For applications where voltage offset errors exist, the ZERO CHECK and OFFSET functions can be used, thereby maintaining maximum instrument accuracy. Current suppression is also available up to 5mA, useful for suppressing background currents, such as dark currents.