Measurement Computing USB-2408 Series - Manual (Page 15)

USB-2408 Series User's Guide Functional Details
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Figure 7 shows a typical TC connection.
Figure 7. DIFF TC connection example
Noise filtering, data rate and throughput rate
Although the USB-2408 Series A/D converter has a maximum data rate of 3,750 samples per second, the actual
throughput rate you observe for voltage and temperature data is determined by these formulas.
 Maximum single-channel throughput:
 Maximum multiple-channel throughput:
where n is the number of channels
See Table 18 and Table 19 in the Specifications chapter for details.
This drop-off in throughput rate is due to the noise filtering feature in the device. You can control the amount of
the noise filtering by adjusting the data rate setting. By reducing the data rate, the averaging of samples
increases, and noise drops correspondingly.
Figure 8 illustrates this inverse relationship. This graph applies to the A/D converter only – do not expect this
level of performance from a USB-2408 Series device itself.
Figure 8. USB-2408 Series A/D converter data rate vs. noise graph
If low noise is your main concern, you can operate the USB-2408 Series device at very low data rates starting
from 2.5 samples per second (S/s). At low rates, much of the noise is averaged out of the data, and issues such
as reference noise become less important.