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OMB-DAQ-2416-4AO User's Guide Functional Details
19
Maximum multiple-channel throughput:
n
μs640
ratedata
1
1
where n is the number of channels
Refer to the tables in the Throughput rate section of the Specifications chapter for details.
This drop-off in throughput rate is due to the OMB-DAQ-2416-4AO's noise filtering feature. 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 12 below illustrates this inverse relationship. This graph applies to the A/D converter only—do not
expect this level of performance from the OMB-DAQ-2416-4AO itself.
Figure 12. OMB-DAQ-2416-4AO A/D converter data rate vs. noise graph
If low noise is your main concern, you can operate the OMB-DAQ-2416-4AO at very low data rates starting
from 2.5 S/s. At low rates, much of the noise is averaged out of the data, and issues such as reference noise
become less important.
At higher data rates, higher-frequency noise sources are not averaged out and begin to be troublesome. These
noise sources include the noise inherent in the A/D converter itself, which is not reducible.
Since thermocouples can pick up noise in your environment, select a data rate based on the primary noise
frequency. For example, to reduce the effect of 60 Hz noise, select a data rate of 60 (or a sub-multiple of 60,
such as 10 or 20).
Multiple-channel throughput rates
When setting different sample rates for different channels, be aware that the all channels will be sampled within
the same sample window based on the channel with the lowest sample rate.
For example, if you set a 10 Hz data rate for channel 0, and a 50 Hz data rate for channel 1, basically, both
channels pass the same number of samples per second to the host computer. However, more averaging is
performed on channel 0's samples; therefore, channel 0 is sampled at a higher resolution.
The OMB-DAQ-2416-4AO's A/D converter performs averaging, and the number of averages equals
30,000/data rate.
In this example, channel 0 is sampled 3000 times over 100 ms, and all samples are averaged into one sample.
Then, channel 1 is sampled 600 times over 20 ms, and samples are likewise averaged into one sample.
The final samples are available to you at a maximum rate of about 8 Hz (8.245 Hz).