Omega Engineering OM-DAQ-USB-2401 manual Automatic Calibration, Calibration/Scan Arrangement

Software 4

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 an 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 decreases as the measurement duration speeds up.

NOTE:

When measuring variable input signals (as opposed to relatively steady input signals), the variable signals will require more samples/sec to obtain a realistic signal representation.

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 millisecond), the seven 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 (1 hr/scan) up to 1000 samples/sec (m/scan), and corresponding resolution ranges from 22.5 to 17 bits.

4.10 Automatic Calibration

The DAQ unit contains a built-in source for performing automatic self- calibrations. These calibrations can be performed between scans periodically throughout the measurement process, as indicated in the following figure. Such calibration ensures accurate measurements, even in environments that experience significant temperature fluctuations. The figure below shows an initial calibration followed by the scan/calibrate, scan/calibrate pattern.

NOTE:

The continuous calibration feature is built into the DAQ system. With Auto-Calibration enabled, you may experience slower sample rates especially with multiple chanels turned on.

INITIAL CALIBRATION

SCAN

CALIBRATION

SCAN

CALIBRATION

SCAN

CALIBRATION

0

SCAN PERIOD

TIME

Figure 4-27. Calibration/Scan Arrangement

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