Figure 5-21. Time Base.

Figure 5-20. Typical Portable Ultrasonic Instruments

Figure 5-22. Relationship of CRT Sweep to Time Base

TM-1-1500-335-23 Nondestructive Inspection Methods Manual
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T.O. 33B-1-1 5-22 The sweep, included within the “frame” in Figure 5-22, is a visual presentation of a portion of the time base. Some instruments, such as those with a CRT display, have the following controls to properly align the baseline on the display screen. Figure 5-21. Time Base. a. Horizontal. The horizontal control should be adjusted so that the horizontal baseline (sweep) begins at the left edge of the display. b. Vertical. The vertical control should be adjusted so that the horizontal time base is at zero position of the vertical scale. 5.2.1.3.3 Waveform Visibility. a. Intensity. On a CRT the intensity of the waveform should be adjusted to produce the minimum brightness that makes the waveform clearly visible. b. Background lighting. On some displays the background lighting can be continuously adjusted from 0- 100 percent for optimum waveform visibility. c. Contrast. This is another continuously adjustable control that is used in conjunction with background lighting to produce optimum waveform visibility. d. Focus. On a CRT the focus is adjusted until the baseline is sharp and clear. e. Astigmatism. On a CRT this is used in conjunction with the focus control to sharpen the peaks of the waveform after the baseline is focused. 5.2.1.3.4 Type of Waveform. a. RF (Radio-Frequency display, non-rectified). This type of waveform has the baseline at 50 percent of full screen height and shows the full waveform with both the positive and negative peaks. Although this type of waveform contains all of the signal information, it is not normally used for inspections. It is often used when developing inspection procedures to choose which of the other types of waveforms (listed below) should be used for a particular inspection. b. FW (Full-Wave rectified video display). This type of waveform shows the positive peaks and the negative peaks, but the negative peaks are reversed and made positive. c. HW+ or HWP (Positive Half-Wave rectified video display). This type shows only the positive peaks. d. HW- OR HWN (Negative Half-Wave rectified video display). This type shows only the negative peaks.

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