The vertical linear range of an ultrasonic instrument can be determined by obtaining responses from which reference blocks?

• A. A set of distance amplitude reference blocks
• B. Steel balls located at several different water path distances
• C. A set of area amplitude reference blocks
• D. All of the above

Answer: (C)

Vertical linear range refers to how the instrument’s amplitude (vertical) display responds proportionally to the actual echo strength. To determine this properly, you need a reference that provides echoes with known, consistent amplitude tied to a measurable quantity. Area amplitude reference blocks are designed so the echo amplitude scales with the reflector’s area, giving a reliable, repeatable signal across depths. By using these blocks, you can map and verify where the display's vertical response stays linear and where it starts to saturate.

Distance amplitude reference blocks are used to calibrate how amplitude changes with distance (the DAR response), which is about depth-related amplitude behavior rather than the vertical scale’s linearity. Steel balls at various water path distances test timing and depth calibration rather than the amplitude scale. Therefore, for establishing the vertical linear range, area amplitude reference blocks are the appropriate choice.