The Model 261 Picoampere Source is a secondary standard for use in calibrating picoammeters and electrometers. The output of the Model 261 can be adjusted between 10-‘4A and 1.1 x 10.4A in eight decade ranges. The source has 3 digit resolution for current outputs b#etween 10~12 and 10~4A. The current output of the Mlodel 261 is derived from a variable voltage source and a selectable range resistance. The voltage supply is highly ragulatled for stability and uses highquality components throughoul for reliability. The low side of the output can be floated to avoid possible ground loop problems. 1.2 MODEL 261 FEATURES Important Model 261 features iixlude: 1. 11V Internal Source. The internal voltage source can be set to a value between 0 and 1’lV in O.OlV increments. This permits accurate calibration of picoammeters and electrometers with input voltagt! drops up to 1OmV without calibration correction. 2. Stable High-Meg Resistance Standards. The highmegohm resistance standards are selected for maximum stability. Individual temperature coefficients and resistance values are supplied with each instrument. 3. Line Operation. The Model 261 is line operated from either 105.125V or 210.250V power sources. Voltage selection is easily accomplished with the rear panel line voltage selection switch. 4. Eight Current Ranges. Eight current ranges are user selectable with a single front panel control. 5. Shielded Output Connector. The UHF output connector on the front panel is Teflon@ insulated to minimize possible leakage problems. 6. Floating Low Connection. The low side of the output connection can be floated to miinimize the effects of ground IOOPS.