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Multichannel Scanning Considerations

Last Modified: May 14, 2018

The NI ELVIS III can scan multiple channels at the recommended multichannel sampling rate with different input ranges. However, you must consider several issues when designing your measurement system to ensure high accuracy of your measurements.

In multichannel scanning applications, accuracy is affected by settling time. When your workstation switches from one analog input channel to another analog input channel, the channel MUX must be switched. If the new analog input channel has a different mode and input range, both the mode and gain selector must be changed in order to set the analog input to the new mode and input range. A certain amount of settling time is required for the analog input circuitry to settle to within an accuracy target after the changes in the channel MUX, mode selector, and gain selector happen. Settling time refers to the time it takes the gain selector to amplify the input signal to the desired accuracy before it is sampled by the ADC. Refer to the Analog Input specifications for specifics.

There are several external factors that can increase the settling time at the desired multichannel sampling rate, which decreases the accuracy of your measurements. To ensure fast settling times, do the following:
  • Use low impedance sources.
  • Use short high-quality cabling.
  • Avoid switching from a large to a small input range.

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