GAMBICA Guide - T&M Sector - Measurement Accuracy - 2025.pdf

01 January 2025

• Electrical Installation Test Instruments
• Electronics Test & Measurement
• Test & Measurement

This GAMBICA Guide focuses on the accuracy and limitations of measurement instruments used for electrical testing, particularly in line with BS 7671 and BS EN 61557 standards in the UK. These standards define the performance and minimum requirements for instruments used in low-voltage electrical installations.

The document focuses on the accuracy and limitations of measurement instruments used for electrical testing, particularly in line with BS 7671 and BS EN 61557 standards in the UK. These standards define the performance and minimum requirements for instruments used in low-voltage electrical installations.

1. Instrument Limitations:

   • Instruments cannot guarantee absolute accuracy or identical readings due to various influencing factors.
   • Awareness of limitations (range, resolution, accuracy) is crucial for accurate tests and interpretations.

2. Part 1: Range, Resolution, and Accuracy:

   • Range: Refers to the full measurement scope of an instrument. Practical limitations lead to segmented display ranges for readability.
   • Resolution: Indicates the smallest measurable change. Poor resolution at extremes of the range may cause errors.
   • Accuracy: Defines how closely measurements align with true values, affected by both design and usage.

3. Part 2: Sources of Error:

   • Instrument and Accessories: Errors can stem from the device or its components, such as test leads.
   • Circuit Under Test: Measurement conditions, like extremes of range (e.g., very low loop impedance), can affect accuracy.
   • Continuity and loop impedance tests are particularly prone to variations.

Understanding an instrument's range, resolution, and accuracy ensures reliable test results, especially under demanding conditions like near supply sources or low impedance scenarios. Recognising and mitigating measurement errors—whether from the instrument, its components, or the test circuit—helps maintain dependable performance. Whenever possible, measurements should be well within the instrument’s stated limits.

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