Acquiring a Waveform of Data Using an External Scan Clock

You generally acquire waveforms by using the board's internal clock. However, you may need to use an external clock to synchronize the measurements to an external source. Using an external scan clock initiates one scan of data (that is, one set of multiple channels) for each pulse on the scan clock. You may also want to use an external scan clock if an irregular sampling period is necessary, as the scan clock input can handle any TTL pulse train up to the maximum scan frequency. This maximum scan clock rate is the same (max_sample_rate_of_the_board / number_of_channels) limitation as with the internal clock.

Using an external scan clock, for each pulse of the scan clock, the internal channel clock times conversions on every channel on in the scan list. The inter-channel delay, or the period between each channel's acquisition, defaults to the maximum speed of the board to obtain a minimum phase delay between each of the channels. In most cases, this minimum phase delay is ideal because you're sampling all channels at nearly the same time. Without more than one A/D converter, however, this is not possible.

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