National Instruments Data Acquisition Device NI USB-621x User Manual page 155

Appendix B Troubleshooting
NI USB-621x User Manual
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
Connecting Analog Input Signals on USB-6215/6216/6218 Devices
sections of Chapter 4,
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
Use Differential Connections with Ground-Referenced Signal Sources
section of Chapter 4,
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:
Channel 0
Channel 1
Figure B-1. AI Sample Clock and AI Convert Clock
AI Convert Clock controls the convert period, which is determined by the
following equation:
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.
Analog Input.
Analog Input, for more information.
1/sample period = sample rate
Convert Period
Sample Period
1/convert period = convert rate
B-2
and
When to
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