T.O. 33B-1-1 5-20 R Z Z Z Z = - + 2 1 2 1 2 100 Where: R = percentage of energy reflected at the interface. Z₂ = acoustic impedance of the discontinuity Z₁ = acoustic impedance of the test material Example:  A tungsten inclusion is found in a piece of titanium.  How much energy will be reflected at the interface if 100% of the sound energy strikes the tungsten? Known from: Table 5-2 Acoustic impedance of tungsten (Z₂) = 14.20 (10⁴ lb/in² - sec) Acoustic impedance of titanium (Z₁) = 3.94 (10⁴ lb/in² - sec) Solution: R = - +     =     = = = 14 20 3 94 14 20 3 94 100 10 26 18 14 100 0 5656 100 0 32 100 32% 2 2 2 . . . . . . (   . ) . Therefore, 32% of the energy will be reflected at the interface by the tungsten inclusion.  A crack would reflect virtually 100% of the energy because it is filled with air. SECTION II ULTRASONIC EQUIPMENT AND MATERIALS 5.2 ULTRASONIC EQUIPMENT AND MATERIALS. 5.2.1 Basic Ultrasonic Instruments. 5.2.1.1 General Description. All  ultrasonic  instruments  basically  perform  the  functions  of  generating,  receiving  and  displaying  pulses  of  electrical energy  that  have  been  converted  to  and  from  pulses  of  ultrasonic  energy  by  a  transducer/search  unit  attached  to  an instrument.  By properly adjusting an instrument an operator can measure the amplitude of displayed pulse signals and determine the time/distance relationships between generated and received signals.  Detailed instructions for operation of individual models shall be obtained by consulting the operating and maintenance manual for the specific instrument being used. 5.2.1.2 Physical Characteristics of Instrument Controls. The physical nature of the instrument controls varies with the type and age of the instrument.  Older instruments have rotary knobs for fine adjustments, slide switches for coarse adjustments and screwdriver rotary controls for infrequent adjustments of waveform position and visibility.  Newer instruments have push buttons or a sealed membrane keypad both  to  select  the  desired  control  from  a  displayed  menu  and  to  make  the  respective  adjustments  (see  Figure  5-20). Alternatively,  some  menu  driven  instruments  have  a  single  rotary  ("smart")  knob  for  making  adjustments  after  a control has been selected from the menu.