# Translations:Sampling geophysical data/2/en

Recording discrete data samples is carried out as follows: The output signal is sampled with a device that connects at each sampling instant a sample-and-hold amplifier to the amplifier output terminals. The sampling instant itself can be of the order of less than a microsecond. Next, the voltage stored on the sample-and-hold amplifier is compared with a reference voltage in an analog-to-digital converter. This reference voltage changes in a stepwise manner. As a result, the specific voltage interval, or quantum, within which the sample voltage falls can be determined and transmitted in digital form to a recording system. This process is repeated at each discrete time point — say, every 0.004 s (i.e., every 4 ms of data). At intermediate times, the value of the signal voltage is ignored. Of course, representation of a continuous signal by discrete data is an approximation. The closeness of the approximation depends on the sampling time interval as well as on the size of the quantum.