A reference bar is provided to check the instrument zero. The pulse time for the bar isengraved on it. Apply a smear of grease to the transducer faces before placing it on the opposite ends of the bar. Adjust the ‘SET REF’ control until thereference bar transit time is obtained on the instrument read-out.
Having determined the most suitable test points on the materialto be tested, make careful measurement of the path length ‘L’. Apply couplant to the surfaces of the transducers and press it hard onto the surface ofthe material. Do not move the transducers while a reading is being taken, as this can generate noise signals and errors in measurements. Continueholding the transducers onto the surface of the material until a consistent reading appears on the display, which is the time in microsecond for theultrasonic pulse to travel the distance ‘L’. The mean value of the display readings should be taken when the units digit hunts between two values.