The Keithley 642 Electrometer is a MOSFET-based instrument for precision measurement of extremely low currents, high resistances, and electrical charge. It delivers direct digital readout via a five-digit LED display with 19,999 count resolution, engineered for physics, materials science, and electronics applications demanding high accuracy and exceptional stability.
Technical Specifications
DC Ammeter Mode
• Current measurement range: 10 aA to 200 nA
• Input current: < 5 × 10⁻¹⁷ A at 25°C ±1°C
• Voltage burden: < 1 mV typical
• Noise: 8 × 10⁻¹⁷ A rms (2 × 10⁻¹⁶ A peak-to-peak)
• Settling time: 40 ms on 10⁻¹⁰ A range with 22 ms time constant
• Accuracy: ±(0.3% + 5 counts) at 25°C ±1°C over 6 months, exclusive of noise
• Self-generated alpha pulses: < 15 per hour
DC Voltmeter Mode
• Voltage range: 10 µV to 10 V
• Input resistance: 10¹⁶ Ω (10,000 TΩ)
• Input capacitance: < 2 pF typical
• Noise: < 20 µV rms (100 µV peak-to-peak)
• Zero stability (24 hours, ±3°C): ±180 µV
• Temperature coefficient (outside ±3°C): ±(30 µV + 0.5 count)/°C
Coulometer Mode (Charge Measurement)
• Charge range: 4 × 10⁻¹⁶ C to 10⁻¹⁰ C (800 aC to 100 pC)
• Input current: < 5 × 10⁻¹⁷ A at 23°C ±1°C
• Accuracy: ±(0.3% + 5 counts) at 23°C ±1°C over 6 months, exclusive of noise
• Noise: 8 × 10⁻¹⁶ C rms on 0.1 range
• Charge error from zero check: typically 10⁵ dynamic range
• Five 0.5-inch LED digits with decimal point and polarity indication
– Typical Applications
Surface charge measurement, leakage current quantification, photodiode characterization, high-impedance device testing, and precision electrostatic analysis in research and manufacturing environments.
