Keithley 181 Nanovoltmeter

The Keithley 181 Nanovoltmeter is a high-sensitivity DC voltmeter engineered for precision measurements at the nanovolt level. It delivers 10nV resolution across seven voltage ranges spanning 2mV to 1000V, supported by a specialized low-noise front-end and microprocessor-based control. The instrument achieves sub-microvolt accuracy on millivolt ranges and integrates a 3-pole digital filter with selectable time constants to minimize noise and settling time. A seven-digit LED display provides real-time measurement feedback with polarity indication and overload status.

– Technical Specifications

• Measurement Type: DC Voltage
• Resolution: 5½ or 6½ digits; 10nV on 2mV range
• Voltage Ranges: Seven ranges from 2mV to 1000V
• Sensitivity: 10nV
• Zero Stability: Typically 10nV/°C for temperature changes <2°C/hr
• Noise Floor: 1GΩ on mV ranges; 10MΩ on V ranges (2V–1000V)
• Maximum Input: 120V on mV ranges; 1000V on V ranges
• Common Mode Rejection: >90dB (mV ranges); >80dB (V ranges); >60dB (1000V range) at 50/60Hz
• Display: Seven-digit, 13mm LED with decimal point and polarity indication

– Key Features

• Microprocessor-controlled programmability for automated measurement sequences
• Selectable 3-pole digital filter with RC time constants of 0.5, 1, or 2 seconds
• Adjustable damping function for optimized filter response and measurement speed
• Temperature coefficient specifications from ±(0.002% + 3 digits)/°C on 2mV range to ±(0.002% + 0.2 digits)/°C on 200mV–1000V ranges
• 24-hour accuracy to ±(0.006% + 5 digits) on 2mV range at 22–24°C
• 1-year accuracy to ±(0.006% + 2 digits) on mV ranges across 18–28°C
• Analog output with ±0.15% accuracy

– Typical Applications

• Thermal EMF and thermoelectric measurement
• Low-level sensor signal acquisition
• Bridge and potentiometer measurements
• Electrochemistry and biomedical instrumentation testing

– Compatibility & Integration

Analog output enables integration with external recording systems and data acquisition platforms. High input impedance on mV ranges minimizes loading effects on high-impedance signal sources.