The Fluke 845AR is a high-impedance DC voltmeter and null detector engineered for precision measurement applications requiring exceptional input impedance, sensitivity, and isolation. This solid-state instrument delivers accurate DC voltage measurements across 19 ranges from 1 µV to 1000 V, making it essential for laboratory, test, and calibration work where source loading must be minimized and measurement fidelity is non-negotiable.
## Technical Specifications
**Measurement Ranges:** 19 ranges, 1 µV to 1000 V DC with X1 and X3 progression.
**Input Resistance:** Better than 10¹⁰ Ω at 80% RH and 35°C; improves to better than 10¹³ Ω with driven guard. Range-dependent impedance: 100 MΩ (300 mV and above), 10 MΩ (3 mV to 100 mV), 1 MΩ (1 mV and below). Null detector mode on ranges 100 mV and below: 10 MΩ input impedance.
**Input Voltage Isolation:** Input floatable to 1100 V above ground. Leakage isolation: better than 10¹² Ω regardless of power, chassis ground, or guard connections; better than 10¹² Ω at less than 50% RH and 25°C.
**Overload Protection:** 1100 V on all ranges with approximately 4 second recovery time.
**Accuracy:** ±(3% of end scale + 0.1 µV) for Fluke 845AR; ±(2% of end scale + 0.1 µV) for Fluke 845AB.
**Common Mode Rejection (DC):** Better than 160 dB (short-circuited, 80% RH); better than 140 dB (open, 50% RH); better than 120 dB (open, 80% RH). Derates 20 dB across 0–50°C. AC rejection (below 100 kHz): 100 Vrms or 120 dB greater than end scale (whichever is less) with less than 2% end scale error.
**Normal Mode Rejection (AC, 60 Hz and above):** AC voltages 60 dB above end scale with less than 2% end scale error. Maximum 750 Vrms.
**Zero Stability:** Better than 0.15 µV/hour and 0.3 µV/day. Temperature coefficient: less than 0.1 µV/°C (15–35°C); less than 0.2 µV/°C (0–50°C). Zero control range: ±5 µV minimum.
**Recorder Output:** 0–1 V DC, linear to 0.5% end scale. Isolated from input. Maximum gain: 120 dB. Source impedance: 5 kΩ to 7.5 kΩ.
**Power:** 115/230 VAC ±10%, 50–440 Hz, approximately 3 W.
## Key Features
• Extreme input isolation eliminates source loading effects
• Isolated recorder output enables direct integration with data acquisition systems
• Driven guard option elevates input impedance to 10¹³ Ω
• Overload protection to 1100 V
• Sub-microvolt zero stability and drift
## Typical Applications
• Thermocouple and sensor bridge measurement
• Potentiometer calibration and comparison
• Null detection in precision test circuits
• Low-level DC signal acquisition in shielded environments
## Compatibility & Integration
Standard EIA 19-inch relay rack mount with resilient benchtop feet. Isolated 0–1 V DC recorder output for chart recorders, data loggers, and instrumentation interfaces.
