Keithley 485
Autoranging Picoammeter, 4.5 Digits

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Product Overview

The Keithley 485 Autoranging Picoammeter is a low-cost, highly sensitive, easy-to-use instrument. The input can withstand extrememly high overloads for flexibility in a wide range of applications in test, research, and student labs. An analog output linearly converts the incoming current to voltage for hard copy output or control loop applications. The Keithley 485’s input voltage drop (burden) is actively constrained by feedback techniques so that this picoammeter makes high accuracy current measurements even in circuits with very low source voltages.

The Keithley 485 has several features that facilitate measuring low current. In the autorange mode, this picoammeter maximizes resolution. The REL button makes readings relative to the baseline (the reading prior to touching the button). The LOG button converts the display to the logarithm (base 10) of the absolute value of the measured current. Digital calibration is performed from the front panel or over the bus. A 100-point data store buffer collects and stores measurements at one of six automatic reading rates from three per second to one per hour, or manually with the STORE button. Minimum and maximum readings are continuously updated at three per second in the data store mode.

Features and Specifications of the Keithley 485 Autoranging Picoammeter include:

• 100fA sensitivity
• Low Voltage Burden:
  • More accurate measurement
  • Makes the 485 closer to an ideal ammeter
• Log I readings
• Optional IEEE-488 interface
• Optional Rechargeable Battery Pack:
  • Picoammeter can be battery operated
  • Provides isoation from the power line
  • Provides portability
• Input Voltage Burden:  <200μV
• Ranging:  Manual or autoranging
• Autoranging Time:  Average 250 msper range change
• Settling Time at Display: 
• Conversion Period:  300ms
• Temperature Coefficient:  (0°–18°C & 28°–50°C): ±(0.1 × applicable accuracy specification)/°C
• Maximum Common Mode Voltage:  30V rms, DC to 60Hz sine wave
• Analog Output:
  • Output Voltage:  +1V = –10000 counts, except +100mV = –10000 counts on 2nA range
  • Output Resistance:  1kΩ
• REL:
  • Pushbutton allows zeroing of on-range readings
  • Allows relative readings to be made with respect to baseline value
  • Front panel annunciator indicates REL mode
• Data Store and Min/Max:
  • 100 reading storage capacity
  • Records data at one of six selectable rates from 3 readings/second to 1 reading/hour, or by manual triggering
  • Also detects and stores maximum and minimum readings continuously while in the DATA STORE mode
• Log:
  • Displays logarithm (base 10) of the absolute value of the measured current
  • (examples: –3.000 = ±1mA; –6.301 = ±0.5μA)