T.O. 33B-1-15-21Figure 5-20. Typical Portable Ultrasonic Instruments5.2.1.3 WaveformDisplayControls.An ultrasonic instrument may have one of several types of waveform display: traditional cathode ray tube (CRT), liquidcrystal display (LCD), or electroluminescent display. Controls affecting the waveform display are discussed below.5.2.1.3.1 ScaleIllumination.CAUTIONWith a CRT, if the intensity is allowed to remain at a high level for long periods, itis possible to permanently burn the display.The horizontal and vertical scales are illuminated in various ways. On some instruments the scales are scribed on thefaceplate and cannot be illuminated. On a CRT the brightness control for the scales may be integrated with a rotarypower switch or may be a separate control. Other types of display may simply have an on/off switch for illuminationcontrol.5.2.1.3.2 WaveformPositioning.The events in an ultrasonic inspection are related to time that is referenced to the pulses produced by the instrument.Figure 5-21 illustrates time as seen on a display: a horizontal line called the time base or baseline. Time starts at theleft end of the time base and progresses to the right. The horizontal line appearing on a display is called the sweep.
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