Keithley 485 Autoranging Picoammeter

The Keithley 485 Autoranging Picoammeter measures DC currents from 100 fA to 2 mA with 4½-digit resolution and autoranging across seven decades. Designed for research, development, and quality control applications requiring picoampere-level accuracy, the instrument delivers 100 fA sensitivity on its most precise range with a minimal voltage burden below 200 µV. This ensures measurement integrity in low-source-voltage circuits while maintaining high input isolation exceeding 5×10¹¹ Ω.

## Technical Specifications

• **Current Range:** 100 fA to 2 mA full scale across seven autoranging decades
• **Resolution:** 4½ digits (19999 counts); 100 fA least significant digit on 2 nA range
• **Accuracy:** 0.4% ± 4 counts (one-year, 2 nA range); Temperature Coefficient: ±(0.1 × applicable accuracy specification)/°C from 0–18°C and 28–50°C
• **Voltage Burden:** Less than 200 µV on all ranges
• **Input Isolation:** Typically greater than 5×10¹¹ Ω in parallel with less than 1 nF
• **Maximum Common Mode Voltage:** 30 V rms, DC to 60 Hz sine wave
• **Maximum Continuous Input Voltage:** 220 VDC
• **Overload Withstand:** 1000 V with 100 kΩ limiting resistor
• **Maximum Input Capacitance:** 10 nF (nA ranges, 2 µA range); 1 µF (20 µA, 200 µA, mA ranges)
• **Display:** 4½-digit LCD, 0.5 inch character height with polarity, range, and status indicators
• **Settling Time:** Less than 1 second to within 2 counts on fixed range
• **Conversion Period:** 300 ms
• **Autoranging Time:** Average 250 ms per range change
• **NMRR (50/60 Hz):** 60 dB

## Key Features

• Manual or automatic range selection
• REL button for zeroing on-range readings against baseline values
• LOG button converts display to base-10 logarithm of absolute measured current
• 100-reading data storage with selectable acquisition rates from 3 readings/second to 1 reading/hour, plus manual trigger option
• Real-time minimum and maximum value tracking in data store mode
• Front-panel or bus-accessible digital calibration
• Analog output: +1 V = −10000 counts (±100 mV = −10000 counts on 2 nA range) with 1 kΩ output impedance

## Typical Applications

Photodiode characterization, leakage current measurement, radiation detection, surface insulation resistance testing, and semiconductor device analysis.

## Compatibility & Integration

Optional IEEE-488 (GPIB) interface available (Model 4853) for fully programmable computer control.