Digital multimeters measure voltage, current, and resistance and are fundamental to electrical testing. Calibration verifies each measurement function against traceable reference standards across all ranges. Accurate multimeter readings are essential for troubleshooting, production testing, and safety compliance.
Power on the multimeter and allow it to warm up for the manufacturer-recommended period (typically 30-60 minutes). Connect to the calibrator output terminals using short, low-thermal-EMF test leads.
Test DC voltage on each range by applying known voltages at 0%, 10%, 50%, 90%, and 100% of the range. Record the multimeter reading at each point. Start from the lowest range and work upward.
Test AC voltage on each range at multiple frequencies (typically 50/60 Hz, 1 kHz, and 10 kHz). Apply known voltages at 10%, 50%, and 100% of range. Record the multimeter reading at each combination of voltage and frequency.
Test current functions on each range at 10%, 50%, and 100% of range for both DC and AC. Use appropriate current terminals and observe maximum input time limits to prevent heating effects.
Test resistance on each range using known resistance values at 10%, 50%, and 100% of range. Use four-wire connection for low-resistance ranges. Ensure reference resistors have adequate thermal stability.
If the multimeter includes frequency, capacitance, temperature, or diode test functions, verify each using appropriate reference standards. Record readings and calculate errors for each function and range.
If errors exceed specifications, perform internal adjustments per the manufacturer's procedure. Record as-found and as-left data for all test points. Generate the calibration certificate with measurement uncertainty for each function.
Error at each test point must be within the manufacturer's published accuracy specification for the applicable function and range. Typical DC voltage accuracy is ±(0.05% of reading + 2 counts) for a 4.5-digit multimeter.
12 months
Most manufacturers specify 30 to 60 minutes of warm-up time before calibration. This allows internal components to reach thermal equilibrium, which is necessary for the accuracy specifications to be valid.
A multifunction calibrator is the most efficient approach, but you can use individual voltage standards, current sources, and resistance standards. The key requirement is that each reference standard has traceable calibration and adequate accuracy ratio (typically 4:1 TUR).
A 4:1 TUR is the traditional target, meaning the reference standard uncertainty should be four times better than the multimeter specification. When 4:1 is not achievable, a decision rule per ILAC-G8 must be applied to manage the risk of false accept.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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