In a basic pulse-echo ultrasonic instrument, the component that produces visible signals on the CRT which are used to measure distance is called:

• A. Sweep circuit
• B. Receiver circuit
• C. Marker circuit
• D. Synchronizer

Answer: (C)

The key idea is that distance is read from reference indicators on the display that show where a known depth would lie in the time axis. In a pulse-echo UT instrument, the echo’s arrival time is translated into depth using the horizontal time base, but to read that depth quickly and accurately you rely on markers—vertical reference lines or lines at set positions that correspond to specific distances. The marker circuit generates these visible indicators on the CRT, so you can directly compare an echo’s location to the markers and read off the distance. The sweep circuit provides the moving horizontal baseline for the trace, the receiver shapes and amplifies the echo, and the synchronizer coordinates timing, but none of these create the distance markers themselves. That’s why the marker circuit is the component that produces the signals you use to measure distance on the display.