Omega OMB-DAQ-54 User Manual page 54

In Personal Daq applications, thermocouples should not be connected single-ended. Doing
so can result in noise and false readings. This is especially true when acquiring other high-
amplitude signals in conjunction with thermocouple signals that are connected single-ended.
Measurement Duration Column
signal. The measurement durations range from very slow (610 milliseconds/sample) to very fast
(12.5 milliseconds/sample). Some related terms are defined as follows:
Sample rate – Samples per second. The sample rate is the number of samples that take place per second.
With a slow measurement duration of 610 milliseconds, there will only be 1.6 samples per second. With a
very fast measurement duration of 12.5 milliseconds, there will be 80 samples per second.
Resolution (Bit 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. Personal 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
measurement duration of 610 milliseconds, the last two bits are considered unreliable, resulting in a
resolution of 22 bits. At a very fast measurement duration (12.5 milliseconds), the nine least significant
bits are unreliable, resulting in 15 bit accuracy.
Speed Designation
Very Slow, 50 / 60 Hz rejection
Slow, 50 Hz rejection
Slow, 60 Hz rejection
Medium, 50 Hz rejection
Medium, 60 Hz rejection
Medium
Fast
Very Fast
1. Each channel can have independent measurement speed and resolution.
Notes:
2. The sample rates shown were obtained with continuous self-calibration disabled.
Personal Daq User's Manual
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Single-Ended and Differential Connections to Analog Inputs
⎯ Indicates the amount of time used for sampling a channel's input
Speed vs. Resolution
Measurement
Duration
(Scan Period)
610 ms
370 ms
310 ms
130 ms
110 ms
40 ms
20 ms
12.5 ms
The table values do not include the use of CJC measurements.
989394
1
Maximum Resolution
2
(Bits RMS)
Sample Rate
(-4 V to +4 V range)
(Samples/sec)
1.6 / sec 22
2.7 / sec 22
3.2 / sec 22
7.7 / sec 21
9.2 / sec 21
25 / sec 19
48 / sec 17
80 / sec 15
Personal DaqView 4-11