Appendix B Troubleshooting
NI USB-621x User Manual B-2 ni.com
reference. There are various methods of achieving this reference while
maintaining a high common-mode rejection ratio (CMRR). These methods
are outlined in the Connecting Analog Input Signals on
USB-6210/6211/6212 Devices and Connecting Analog Input Signals on
USB-6215/6216/6218 Devices sections of Chapter 4, Analog Input.
AI GND is an AI common signal that routes directly to the ground
connection point on the devices. You can use this signal if you need a
general analog ground connection point to the device. Refer to the When to
Use Differential Connections with Ground-Referenced Signal Sources
section of Chapter 4, Analog Input, for more information.
How can I use the AI Sample Clock and AI Convert Clock signals on a
USB-621x device to sample the AI channel(s)?
USB-621x devices use AI Sample Clock and AI Convert Clock to perform
interval sampling. As Figure B-1 shows, AI Sample Clock controls the
sample period, which is determined by the following equation:
1/sample period = sample rate
Figure B-1. AI Sample Clock and AI Convert Clock
AI Convert Clock controls the convert period, which is determined by the
following equation:
1/convert period = convert rate
This method allows multiple channels to be sampled relatively quickly in
relationship to the overall sample rate, providing a nearly simultaneous
effect with a fixed delay between channels.
Channel 0
Channel 1
Convert Period
Sample Period
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