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Single-Ended and Differential Connections to Analog Inputs
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
⎯
Indicates the amount of time used for sampling a channel’s input
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 vs. Resolution
1
Speed Designation
Measurement
Duration
(Scan Period)
Maximum
Sample Rate
2
(Samples/sec)
Resolution
(Bits RMS)
(-4 V to +4 V range)
Very Slow, 50 / 60 Hz rejection
610 ms
1.6 / sec
22
Slow, 50 Hz rejection
370 ms
2.7 / sec
22
Slow, 60 Hz rejection
310 ms
3.2 / sec
22
Medium, 50 Hz rejection
130 ms
7.7
/ sec
21
Medium, 60 Hz rejection
110 ms
9.2 / sec
21
Medium
40 ms
25 / sec
19
Fast
20 ms
48 / sec
17
Very Fast
12.5 ms
80 / sec
15
Notes:
1. Each channel can have independent measurement speed and resolution.
2. The sample rates shown were obtained with continuous self-calibration disabled.
The table values do not include the use of CJC measurements.
Personal Daq User’s Manual
989394
Personal DaqView 4-11
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