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 Keithleys data acquisition boards to implement a very cost-effective, low curreent measurement system with wide bandwidth and fast response.
The Model 428-PROG incorporates a second order Bessel-function filter that mini mizes 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 sca ning tunneling electron microscopes.
Input and output connections to the Model 428-PROG are made with BNC connectors. INPUT HI is connected to a program mable +/-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.
The Model 428-PROG also incorporates an exterior design with simple front panel operation, improved display, and convenient system integration. Pushbutton controls have an LED to indicate if that function is activated. The display features three selectable intensities (bright, dim, and off) for use in light-sensitive environments. All setup values can be displayed from the front panel. An IEEE-488 interface is included.