III. EQUIPMENT FOR ULTRASONIC APPLICATIONS

III. EQUIPMENT FOR ULTRASONIC APPLICATIONS

As with computers, the technology concerning ultrasonic equipment and systems is becoming somewhat transitory. Ultrasonic systems are either battery operated portable units, multicomponent laboratory ultrasonic systems, or something in between. Whether they are based on modern digital technology or the fast disappearing analog original, systems (often defined as instrument plus transducer and cable) basically comprise the following components. The appropriate controls are shown in the ellipses in Figure 7-25.

FIGURE 7-25: Block diagram, analog.

1. Transducer

2. Pulser (clock)

3. Receiver/amplifier

4. Display (screen)

To understand how a typical ultrasonic system operates, it is necessary to view one cycle of events, or one pulse. The sequence is as follows.

1. The clock signals the pulser to provide a short, high-voltage pulse to the transducer while simultaneously supplying a voltage to the time-base trigger module.

2. The time-base trigger starts the spot in the CRT on its journey across the screen.

3. The voltage pulse reaches the transducer and is converted into mechanical vibrations (see piezoelectricity ), which enter the test piece. These vibrations (energy) now travel along their sound path through the test piece. All this time, the spot is moving horizontally across the CRT.

4. The energy in the test piece now reflects off the interface (back wall) back toward the transducer, where it is reconverted into a voltage. (The reconverted voltage is a fraction of its original value.)

5. This voltage is now received and amplified by the receiver/amplifier