The most widely used image quality indicators are three types: wire type image quality indicators, stepped hole type image quality indicators, flat hole type image quality indicators, in addition to slot type image quality indicators and dual wire image quality indicators. Image quality indicators should be made of materials that are the same as the inspected workpiece or have similar radiation absorption properties. Various image quality indicators have designed their own specific structures and detail forms, and defined their own methods for measuring radiographic sensitivity.

Wire type image quality indicator (linear image quality indicator)

The wire type image quality indicator is the most commonly used image quality indicator both domestically and internationally. It is simple in structure and easy to make, and has been widely used by countries all over the world. The International Organization for Standardization has also included wire type image quality indicators in its radiographic standards. The types and specifications of wire type image quality indicators have been basically unified.

The basic style of the wire type image quality indicator is shown in Figures 2-33. It is made of metal wires made of materials that are the same or similar to the material of the workpiece being transilluminated, arranged in parallel with the specified spacing according to the order of diameter, encapsulated in transparent materials with low radiation absorption coefficient, or directly installed on a certain frame, and equipped with certain symbols to indicate letters and numbers. Generally, the corresponding numbers of the metal wires are placed at both ends of the arranged metal wires to identify the image quality indicator of the wire type. The standards of different countries have their own regulations on the diameter and allowable deviation, length, spacing, number of wires in an image quality indicator, and marking instructions of the wires. Some standards for wire materials have made specific provisions. Wire type image quality indicators are mainly used in metal materials.