Advanced Instrumentation and
Experimental Methods
Module code DME 811
Dr Riaz A Mufti
(B.Sc, M.Sc Eng (UK), PhD (UK), CEng (UK), MIMechE (UK), P.E (PEC))
Data Acquisition Hardware and Software
DAQ Hardware Overview
Topics
• Hardware setup
• Components of a DAQ device Software
• Connection types Data
Acquisition
Signal
Conditioning
Signal
Transducer
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Data Acquisition Hardware
DAQ Hardware turns your PC into a measurement and
automation system
Your Signal
Sensors Signal Computer
Connector DAQ Device
• Any type • PCI/PXI • Windows
• Direct
• PCIe/PXIe • Linux
Connection
• USB • Mac (DAQmx
• Terminal Block
Base)
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Configuration Considerations Analog Signal
• Analog Input
− Resolution
− Range
− Amplification
− Code Width
− Mode (Differential, RSE, or NRSE)
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Resolution
• Number of bits the ADC uses to represent a signal
• Resolution determines how many different voltage changes
can be measured
• Example: 12-bit resolution
# of levels = 2resolution = 212 = 4,096 levels
• Larger resolution = more precise representation of your
signal
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Resolution Example
• 3-bit resolution can represent 8 voltage levels
• 16-bit resolution can represent 65,536 voltage levels
16-Bit vs. 3-Bit Resolution
(5kHz Sine Wave)
10.00
111
8.75
110 16-bit resolution
7.50
101
6.25
Amplitude 100 3-bit resolution
5.00
(volts) 011
3.75
010
2.50
001
1.25
000
0 | | | | |
0 50 100 150 200
Time (ms)
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Device Range
• Minimum and maximum voltages the ADC can digitize
• DAQ devices often have different available ranges
➢ 0 to +10 volts
➢ –10 to +10 volts
• Pick a range that your signal fits in
• Smaller range = more precise representation of your signal
− Allows you to use all of your available resolution
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Range = 0 to +10 volts
Range Example 10.00
(5kHz Sine Wave)
111
8.75
Proper Range 7.50
110
101
– Using all 8 levels to Amplitude 6.25
5.00
100 3-bit resolution
(volts) 011
3.75
represent your signal 2.50
010
001
1.25 000
0| | | | |
0 50 100 150 200
Time (ms)
Range = -10 to +10 volts
(5kHz Sine Wave)
10.00 111
7.50
5.00
110
101 3-bit resolution
Improper Range
2.50
Amplitude 0 100
011
– Only using 4 levels to
(volts) -2.50
-5.00
010 represent your signal
001
-7.50 000
-10.00 | | | | |
50 100 150 200
Time (ms)
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Amplification
• Max and min settings amplify or attenuate
the signal for best fit in ADC range
• Settings are 0.5, 1, 2, 5, 10, 20, 50, or 100
for most devices
• You don’t choose the amplification directly
− Choose the input limits of your signal in
LabVIEW or the DAQ Assistant
− Proper amplification chosen by NI-DAQmx
• Proper amplification = more precise
representation of your signal
− Allows you to use all of your available
resolution
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Amplification Example
• Input limits of the signal = 0 to 5 Volts
• Range Setting for the ADC = 0 to 10 Volts
• Amplification applied by Instrumentation Amplifier = 2
Different Amplifications for 16-bit Resolution
(5kHz Sine Wave)
10.00
8.75
Amplification = 2
7.50
6.25
Amplitude Your Signal
5.00
(volts) Amplification = 1
3.75
2.50
1.25
0 | | | | |
0 50 100 150 200
Time (ms)
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Code Width
Code Width is the smallest change in the signal, which your system can detect
(determined by resolution, range, and amplification)
range
code width =
amplification * 2 resolution
Smaller Code Width = more precise representation of your signal
Example: 12-bit device, range = 0 to 10V, amplification = 1
range 10
= = 2.4 mV
amplification * 2 resolution 1* 212
20
Increase range: = 4.8 mV
1 * 212
10
Increase amplification: = 24 μV
100 * 212
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