How to Understand the Resolution of a Geological Detector?

When reviewing specs for a geological detector, groundwater detector, or metal detector, you'll encounter technical notations like "0.1mV ±5%". This specification is critical as it defines the instrument's capability, combining its sensitivity and its reliability. 

It answers two key questions: How small a signal can it see? And how accurate is the reading?

The Two Parts Explained

0.1mV: The Instrument Resolution

This figure represents the instrument resolution—the smallest change in voltage the detector can discern. A resolution of 0.1mV means the device can detect a change of one-tenth of a millivolt. For a geological detector, this high sensitivity is essential for identifying subtle variations in soil or rock properties that indicate fractures, mineral deposits, or water pockets. It’s important to note that resolution is about the finenessof measurement, not its correctness. A high-resolution instrument provides detailed data, but that data may not be perfectly accurate.

±5%: The Measurement Error

The "±5%" is the measurement error, also known as accuracy. It defines the maximum expected deviation of the displayed value from the true value. This relative error means the uncertainty grows with the size of the reading. For a reliable groundwater detector, knowing this error margin is vital for correct data interpretation.A Practical Example Assume your geological detector​ shows a reading of 10.0mV.

• Thanks to the Resolution:​ The device can distinguish between 10.0mV and 10.1mV, allowing you to map fine subsurface details.
• Considering the Error:​ The ±5% error means the true value is within a calculable range:
  • Upper Limit: 10.0mV + (5% of 10.0mV) = 10.5mV
  • Lower Limit: 10.0mV - (5% of 10.0mV) = 9.5mV
  • Conclusion:​ The actual voltage lies between 9.5mV and 10.5mV.

A Key Distinction: Type of Error

Always check the spec sheet to see if the error is a percentage of the readingor the full scale.

• % of Reading (Preferred):​ Error scales with the measurement, as in the example above. This is more accurate for small signals.
• % of Full Scale (Use with Caution):​ The error is a fixed value based on the instrument's maximum range. For a small reading, this can lead to a very large relative uncertainty.

Why It Matters in the Field

For professional surveys, this specification is not just a number. High instrument resolution​ enables the detection of fine geological features, while a clearly defined measurement error​ provides the confidence interval for your data. When modeling subsurface structures, you must account for this potential deviation to avoid misinterpretation.In short, "0.1mV ±5%" tells you that a detector is both highly sensitive and transparent about its accuracy limits. Understanding this balance is key to choosing the right tool and interpreting its data correctly.

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Technical data compiled from customer post-run reports, and published engineering references. No operational guarantee implied.

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