Data Acquisition

acquisition system, is the slowest of either the board throughput, the data transferrate or, if relevant, the storage rate.In most data acquisition systems the storage rate is not significant, since the amount of datainvolved is small enough to allow it all to be stored in memory, left there, displayed ifnecessary, and stored later. The transfer rate of the link from memory to permanent datastorage is therefore not important.Where the volume of data acquired is greater than the memory available to it, andparticularly when the required throughput is very high, then alternative methods of storing thedata must be found.D/A boards convert digital signals from a host computer into an analog format for use byexternal devices such as actuators in controlling or stimulating a system or process. Theprinciple component of all D/A boards is the digital-to-analog converter (D/A Converter).D/A boards fall into two main categories:• Waveform generation boards• Analog output boardsWaveform generation D/A boardsAs their name would imply waveform generation D/A boards are used in the high speedgeneration of analog waveforms, typically in a laboratory environment for the reproduction orsimulation of noise, audio signals, power line signals and also for many other controlapplications.The functional diagram of a waveform generation D/A board is shown in Figure 5.24 andcomprises the following main components:• D/A converter (DAC)• Output amplifier/buffer• FIFO buffer• Timing system• Expansion bus interfaceEach of these components plays an important role in determining the speed, accuracy, andflexibility with which the D/A board can generate analog waveforms.Figure 5.24Functional diagram of a waveform generation D/A board