DAQslides
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Transcript of DAQslides
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BJ Furman SJSU MAE
ME 120 Experimental Methods
Data Acquisition
BJ Furman30SEP02
BJ Furman SJSU MAE
Introduction Data Acquisition (DAQ)
the means by which physical signals, such as voltage,current, pressure, and temperature, are converted into digitalformats and brought into the computer.(LabView Measurements Manual,http://www.ni.com/pdf/manuals/322661a.pdf)
Instrument-based
E.g., Digital oscilloscope
Computer-based
DAQ card that plugs directly into the computer bus andinterfaces to signals directly from transducers or signal
conditioning hardware Ex. NI 6024E
Mixed
Signal analyzer instrument connected to a GP-IB card in a PC
Remote DAQ module connected to a PC
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BJ Furman SJSU MAE
DAQ System Components
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf)
BJ Furman SJSU MAE
Signal I/OAnalog vs. Digital
Analog signal amplitude can take on values over acontinuous range
Ex. Temperature, pressure
Digital signal amplitude takes on only discretevalues
Ex. Logic level 0 or 5 V
Input vs. Output
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf )
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BJ Furman SJSU MAE
Resolution of DAQ Device
Resolution=the smallest increment of voltagechange that can be determined by the device
Determined by the number of bits in the A/D or D/Aconverter and the full-scale range of the device
3-bit vs. 16-bit A/D resolution with 0 to 10 V range
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf )
1 1
16-bit 16
1.0 10 V 1.0 10 V0.15 mV
2 65536
= = =
1 1
3-bit 3
1.0 10 V 1.0 10 V1.25 V
2 8
= = =
What is e3-bit when the
range is 10 to 10 V?
BJ Furman SJSU MAE
Device Range 0 to 10 V range vs. 10 V to 10 V range
3-bit 310 V 10 V 1.25 V2 8
= = =3-bit 3
10 10 V 20 V 2.50 V2 8
= = =
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf)
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BJ Furman SJSU MAE
Effects of Device Limit Settings
0 to 10 Vvs. 0 to 5 V
To maximizeresolution,what shouldyou do?
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf)
BJ Furman SJSU MAE
Grounded vs. Floating Signal Sources Grounded signal sources have
voltage signals that are referencedto a system ground
Ex. Earth ground through 3rd prong
Floating signal sources havevoltage signals that are not
connected to an absolute reference Ex. Battery, thermocouple
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BJ Furman SJSU MAE
Configuring the DAQ Device
Three basic configurations: Differential
Referenced Single-Ended (RSE)
Non-Referenced Single Ended (NRSE)
What are the differences between these? Use differential mode when:
The input signal is low level (less than 1 V).
The leads connecting the signal to the device are greater than 3m (10 ft).
The input signal requires a separate ground-reference point or
return signal. The signal leads travel through noisy environments.
Note: requires 2 channels per!
BJ Furman SJSU MAE
Differential Mode
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf)
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BJ Furman SJSU MAE
Referenced Single-Ended Inputs
Use Referenced Single-Ended mode when: The input signal is high level (greater than 1 V).
The leads connecting the signal to the device are less
than 10 ft (3 m).
The input signal is floating
BJ Furman SJSU MAE
Referenced Single-Ended Mode (RSE)
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf)
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BJ Furman SJSU MAE
Non-Referenced Single-Ended Inputs (NRSE)
Use Non-Referenced Single-Ended mode when: The input signal is high level (greater than 1 V).
The leads connecting the signal to the device are less
than 10 ft (3 m).
The input signal is referenced to ground
BJ Furman SJSU MAE
Non-Referenced Single-Ended Mode
(LabView Measurements Manual, http://www.ni.com/pdf/manuals/322661a.pdf)
