ISO 16526-2:2011

Overview

ISO 16526-2:2011 specifies a practical constancy check for X‑ray systems - the thick filter method - used in non‑destructive testing (NDT) to monitor changes in the X‑ray tube voltage, tube current and target condition (ageing). The method measures the dose rate behind a defined thick filter at fixed distances between X‑ray tube, filter and dose meter. It is highly sensitive to voltage changes but does not provide an absolute kV value; a reference value (typically from the system acceptance test) is required for comparison.

Key topics and technical requirements

• Purpose: regular constancy checks and post‑component‑change consistency checks for X‑ray systems.
• Applicability: constant potential, half‑wave and impulse‑wave generators with tube current > 1 mA.
• Equipment and setup:
  • X‑ray system, specified collimator, thick filter, suitable dose meter / dose‑rate meter, film for collimation proof.
  • Fixed focus‑to‑filter and focus‑to‑meter distances for the reference and all subsequent tests.
  • Collimator diameter as small as possible; homogeneous irradiation area at the detector ≤ 3× detector chamber size (verified by film).
• Measurement control:
  • Determine the leverage factor (L) for the chosen setup by measuring dose at 100% and 95% of the test voltage. A leverage factor between about 6 and 8 is recommended for good sensitivity.
  • Select exposure time to yield readings between 50% and 100% of meter scale; take three or more measurements and average.
  • Dose meter long‑term stability should be at least 3× better than the required tolerance; regular stability checks (e.g., with a radioactive source) are required.
• Result evaluation and documentation:
  • Constancy is confirmed if the measured dose/dose‑rate reproduces within the calculated tolerance (derived using the measured leverage factor).
  • Test report must document system ID, X‑ray parameters, collimator and filter details, distances, meter ID, measured values, leverage factor, deviation from reference, date and operator signature.

Applications and users

• Intended for operators and maintenance personnel of industrial X‑ray inspection systems who need a simple, repeatable routine check of voltage stability.
• Useful in manufacturing, weld inspection, aerospace, petrochemical and service labs for:
  • Periodic stability monitoring
  • Verification after repairs or component changes that may affect tube voltage
  • Operator-level constancy checks between formal calibrations

Related standards

• ISO 16526-1: Voltage divider method (absolute measurement for constant potential systems)
• ISO 16526-3: Spectrometric method (non‑invasive energy‑spectrum based measurement)

Keywords: ISO 16526-2:2011, thick filter method, X‑ray tube voltage measurement, constancy check, NDT, dose rate, leverage factor, dose meter, collimator.