Section 5 – Signal Management
5.1 Channel Control and Expansion
In the OM-DAQ-USB-2401 system, the quantities and types of DAQ units used
determine the system’s channel capacity. Up to 10 OM-DAQ-USB-2401s can be
used with one host PC. See the Specifications for more detailed channel
information.
5.2 Scan Time and Resolution
5.2.1 Scan Time
Scan Time (per scan) - The amount of time used for scanning (sampling) all
selected channels’ input signal. For the OM-DAQ-USB-2401, the scan rates range
from very slow (1 hour per scan) to very fast (1 milliseconds per scan).
5.2.2 Resolution (Effective Number of Bits – ENOB, RMS)
Resolution (Effective Number of Bits - ENOB, RMS) – The number of reliable
data bits that exist for a signal’s measurement. The greater the resolution, the
more detailed the reading, for example, with increased resolution a reading of
5.12 V could become 5.11896 V. The DAQ actually provides for 24 bits of data
information; however, the accuracy of the least significant bits becomes less as
the measurement duration speeds up.
At a scan time greater than 6.5 seconds, the last 1.5 bits are considered unreliable,
resulting in a resolution of 22.5 bits. At a very fast scan time ( 1 milliseconds), the
seven most least significant bits are unreliable, resulting in 17 bit accuracy.
When you select the Scan Time you also determine the scan(sample) rate and
resolution for the applicable channel. For the DAQ’s analog input applications,
scan(sample) rates range from 0.0002778 samples/sec up to 1000 samples/sec
and corresponding resolution ranges from 22.5 to 17 bits.
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