Multiplexed Versus Simultaneous Sampling

NI-DAQmx 18.6 Help


Edition Date: January 2019
Part Number: 370466AH-01
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Devices use either multiplexed or simultaneous sampling. Simultaneous sampling devices have an ADC for each analog channel and can sample from all channels at the same time, as shown in the following figure.



Multiplexed sampling devices have a single ADC for all analog input channels. These devices use both a sample clock and a convert clock. The sample clock initiates the acquisition of a sample from all channels in the scan list. The convert clock causes the ADC conversion for each individual channel. The following figure depicts a three-channel analog input task on a device that uses multiplexed sampling. Notice that, unlike S Series devices, the samples are not digitized simultaneously.



The convert clock must run faster than the sample clock to achieve the specified sample rate. For instance, if you specify a sample rate of 10 S/s for 8 analog input channels, the convert clock must run at least eight times the sample rate (80 Hz) to ensure that each channel is sampled 10 times a second. At faster sampling rates, you must also take settling time between channels into account.

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