Horizontal Linearity of Instrument

T.O. 33B-1-1 1-58 1.8.2.2 Horizontal Linearity of Instrument. 1.8.2.2.1 Definitions. a. Horizontal Limit is the maximum readable length of horizontal deflection that is determined either by an electrical or a physical limit in the A-scan presentation of an ultrasonic testing instrument. Horizontal limit is expressed as the maximum observed deflection in inches from the left side, or the start, of the horizontal line representing the time base. The horizontal limit is full scale. b. Horizontal Linearity Range is the range of horizontal deflection in which a constant relationship exists between the incremental horizontal displacement of vertical indications on the A-scan presentation and the incremental time required for reflected waves to pass through a known length in a uniform transmission medium. The acceptable horizontal linearity range is 85 percent of the Horizontal Linearity Range. 1.8.2.2.2 Procedure for Determining Horizontal Linearity. In lieu of any specific linearity requirement, the horizontal linearity may be checked as follows: a. Use the IIW block and a straight beam search unit (see Figure 1-12). Figure 1-12. Use of IIW Block Horizontal Linearity. b. Place the search unit on the IIW block and adjust the gain, sweep, and sweep delay to obtain six back reflections on the CRT. The first back reflection should be located at the left side of the base line (the initial pulse will be off screen), and the 6th back reflection should be located at the right side of the base line.