National Instruments Data Acquisition Device NI USB-621x, Руководство пользователя

Страница: 155 / 185

Appendix B Troubleshooting
NI USB-621x User Manual B-2 ni.com
are vario u s methods of achieving this reference while maintaining a high
common-mode rejection ratio (CMRR). These methods are o u tlined 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 ro u tes directly to the gro u nd
connection point on the devices. Yo u can u se this signal if yo u need a
general analog gro u nd 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-621
x device to sample the AI channel(s)?
USB-621 x devices u se AI Sample Clock and AI Convert Clock to perform
interval sampling. As Fig u re B-1 shows, AI Sample Clock controls the
sample period, which is determined by the following eq u ation:
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 eq
u ation:
1/convert period = convert rate
This method allows m u ltiple channels to be sampled relatively q u ickly in
relationship to the overall sample rate, providing a nearly sim u ltaneo u s
effect with a fixed delay between channels.
Ch a nnel 0
Ch a nnel 1
Convert Period
Sa mple Period