Measurement-computing Personal Daq rev.6.0 Instrukcja Użytkownika Pobierz pdf (Strona 53)

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

Speed Designation Measurement

Duration

(Scan Period)

Maximum

Sample Rate

(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.

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Measurement-computing Personal Daq rev.6.0 Instrukcja Użytkownika Strona 53