The Fluke 931B RMS Differential Voltmeter is a precision instrument for accurate AC voltage measurements across wide frequency ranges using differential thermocouple transfer standard technology. It delivers true RMS response through thermocouple heating effects, enabling rapid measurements of non-sinusoidal and distorted waveforms. With differential input capability and dual operational modes, it serves calibration laboratories and demanding test environments requiring sub-0.05% accuracy.
Technical Specifications
The 931B operates as both a differential voltmeter and electronic voltmeter. In differential mode, it measures 0.01 V to 1100 V RMS across five ranges (0.1 V, 1 V, 10 V, 100 V, 1000 V) with 10% overranging. Electronic voltmeter mode extends to eleven ranges from 0.003 V to 1100 V RMS in 1-3 sequence, also with 10% overranging capability.
Frequency response varies by operating mode: null damping mode covers 2 Hz to 10 Hz, while normal differential mode spans 10 Hz to 1 MHz. Electronic voltmeter mode extends to 2 MHz. The instrument guarantees true RMS accuracy of ±0.05% of reading across supported bandwidths.
Crest factor handling reaches 10 at full scale (1500 V peak maximum) in differential mode. Electronic mode increases to 30 at 1/3 scale. Input impedance is 1 MΩ shunted by less than 8 pF at the front panel BNC connector.
– Key Features
• Differential input design enables precision comparative voltage analysis
• True RMS thermocoupler response eliminates waveform shape dependencies
• Short-term stability better than 0.005% per hour and 0.02% per day
• Long-term stability better than 0.01% over 30 days using front panel CAL control
• Line regulation exceeds 0.0005% for ±10% supply voltage variation
• AC output proportional to meter deflection (±1% of end scale accuracy) supports external recording and conversion applications
• Rechargeable nickel-cadmium battery provides up to 22 hours operation
– Typical Applications
Calibration of AC voltage standards, laboratory AC waveform analysis, verification of power quality in non-sinusoidal environments, and precision AC measurement traceability.
– Compatibility & Integration
AC output available for RMS-to-DC conversion and direct recording interfaces.
