Analogue-to-digital

The sample frequency of the ADC (analogue to digital converter) should be 8 times higher than the test frequency (centre frequency of the spectrum). In dependence of the application, different ADC- boards are used. A standard board (20520) provides 8 bit resolution and up to 100 Msamples/s in single shot mode. For manual tests, up to 400 Msamples/s can be reached in the repetition mode. For scanning systems with high frequencies boards up to 400 Msamples/s (single shot) are available. 

In order to test a wide range of materials a series of ultrasonic pulser/receiver boards has been developed. In combination with an ADC-board (analogue-to-digital converter) a PC can be converted to a high performance ultrasonic system not only for manual testing but also for automatic testing and imaging systems. 

Fig. 6. Impact of field bus on wiring costs, where A/D and D/A correspond to analogue-to-digital and digital-to-analogue converters, respectively LCU = local control unit and I/P = current-to-pressure transducer, (a) DCS without remote terminal rooms (b) DCS with remote terminal rooms and...

C = transmitter D = signal transmission E = analogue-to-digital converter(A/D) F = digital-to-analogue converter (D/A) ... 

LVDT—linear variable differential transformer, A/D—analogue to digital, VDU—visual... 

A second factor that can influence quantitation is digital resolution in the intensity direction (or vertical scale in the graph). This is due to the analogue to digital converter (ADC) and sometimes can be experimentally corrected by changing the receiver gain. However, for most modern instrumentation this limitation is not so serious and, therefore, will not be discussed in detail below, but is illustrated in Problem 3.7. 

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