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Calibration and Voltage Drift

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Overview

Every HPVM and HPVM Pro is factory-calibrated using a professional bench power supply before it ships. However, long wire runs between your battery and the voltmeter introduce resistance that can cause the displayed voltage to read slightly lower than the true voltage at the source. The voltage drift adjustment in the LF Audio AuralSync app lets you compensate for this to maintain lab-grade accuracy in your specific installation.

Factory Calibration Process

At the factory, each unit goes through the following calibration procedure:

  1. A calibrated bench power supply feeds a known, stable voltage into the unit (e.g., 13.543V).
  2. Local capacitors on the input minimize voltage ripple during calibration to ensure clean, stable readings.
  3. The firmware is commanded to calibrate — it takes multiple samples (typically 10) and computes the offset for each ADC (analog-to-digital converter) input pin.
  4. The drift offset for each channel is programmed into the unit's non-volatile memory.
  5. The result is a unit that reads the correct voltage to three decimal places, matched to a professional reference instrument, right out of the box.

Why Drift Occurs in Your Vehicle

Even with factory calibration, your installation introduces variables that the factory cannot account for:

  • Wire resistance — The longer the wire run from your battery or bus bar to the HPVM, the more resistance is in the measurement path. Resistance causes a voltage drop proportional to the current flowing through the wire, meaning the voltage at the voltmeter's input pin may be slightly lower than the true voltage at the source.
  • Connector resistance — Crimped connections, ring terminals, and fuse holders all add small amounts of resistance.
  • Ground path resistance — A poor ground connection can cause the measured voltage to read incorrectly in either direction.

Adjusting Voltage Drift in the App

The AuralSync app allows you to apply a per-channel drift offset to compensate for your specific installation:

  1. Connect to your HPVM in the AuralSync app.
  2. Open the device settings (gear icon).
  3. Locate the Drift setting for each channel.
  4. Compare the voltage shown on the HPVM to a known-accurate reference (e.g., a calibrated multimeter placed directly at the voltage source).
  5. Adjust the drift value up or down until the HPVM reading matches the reference.
    Tip

    Measure the reference voltage at the source (battery terminal or bus bar), not at the HPVM's input wire. The difference between the two readings is the resistance-induced drop you are compensating for.