1. Data Acquisition (DAQ)
Hardware and software
modern electronic instrumentation unit 5

2. modern electronic instrumentation unit 5
Data Acquisition (DAQ)
Data acquisition is the process of collecting and measuring electrical signals and sending them to a computer for processing.
DAQ systems capture, measure, and analyze physical phenomena from the real world
modern electronic instrumentation unit 5

3. Classification of signal
Analog- DC
- Waveform (time domain)
Waveform (frequency domain)
Digital -- level
Pulse and Wave-train
Vary slowly with time
Require precise timing
Require Powerful PC
Simple Digital I/O
modern electronic instrumentation unit 5

4. modern electronic instrumentation unit 5
A data acquisition system consists of many components that are integrated to:
Sense physical variables (use of transducers)
Condition the electrical signal to make it readable by an A/D board
Convert the signal into a digital format acceptable by a computer
Process, analyze, store, and display the acquired data with the help of software
modern electronic instrumentation unit 5

5. Data Acquisition System Block Diagram
modern electronic instrumentation unit 5

6. modern electronic instrumentation unit 5
Transducers
Sense physical phenomena and translate it into electric signals.
Examples:
Temperature
Pressure
Light
Force
Displacement
Level
Electric signals
ON/OFF switch
modern electronic instrumentation unit 5

7. modern electronic instrumentation unit 5
Signal Conditioning
Electrical signals are conditioned so they can be used by an analog input board. The following features may be available:
Amplification
Isolation
Filtering
Linearization
modern electronic instrumentation unit 5

8. modern electronic instrumentation unit 5
Analog
Signal is continuous
Example: strain gage. Most transducers produce analog signals
Digital
Signal is either ON or OFF
Example: light switch.
modern electronic instrumentation unit 5

9. modern electronic instrumentation unit 5
A/D converter
The trade-off usually falls between 1- Resolution (bits) & Code Width 2- Sampling rate (samples/second) 3- Number of channels, and data transfer rate (usually limited by “bus” type: USB, PCI, PXI, etc.).
modern electronic instrumentation unit 5

10. modern electronic instrumentation unit 5
Resolution
Precision of the analog to digital conversion process is dependent upon the number (n) of bits the ADC of the DAQ uses.
The higher the resolution, the higher the number of divisions the voltage range is broken into (2^n), and therefore, the smaller the detectable voltage changes.
modern electronic instrumentation unit 5

11. modern electronic instrumentation unit 5
Code width
Code width is the smallest change in a signal that a DAQ system can detect
• Calculated using the formula
Code width
Where D is DAQ device input range and n is the resolution
• Larger resolution implies smaller code width and Larger resolution implies smaller code width and more accurate representation of the signal
modern electronic instrumentation unit 5

12. modern electronic instrumentation unit 5
Code Width
For example, a 12-bit DAQ device with a 0 to 10 V input range detects a 2.4 mV change, while the same device with a -10 to 10 V input range would detect a change of 4.8 mV.
modern electronic instrumentation unit 5

13. modern electronic instrumentation unit 5
Sampling Rate
Determines how often conversions take place.
The higher the sampling rate, the better.
Analog
Input
4 Samples/cycle
8 Samples/cycle
16 Samples/cycle
modern electronic instrumentation unit 5

14. modern electronic instrumentation unit 5
For accurate frequency representation:
Sample at least 2x the highest frequency signal being measured
• For accurate shape representation
– Sample 5–10x the highest frequency signal being measured.
modern electronic instrumentation unit 5

15. modern electronic instrumentation unit 5
Connecting to board
Three options available
Differential (Diff)
Referenced to a common signal reference (Non-referenced Single Ended -NRSE)
Referenced to a safety ground (Referenced Single Ended-RSE)
modern electronic instrumentation unit 5

16. modern electronic instrumentation unit 5

17. Data Acquisition Software
It can be the most critical factor in obtaining reliable, high performance operation.
Transforms the PC and DAQ hardware into a complete DAQ, analysis, and display system.
Different alternatives:
Programmable software.
Data acquisition software packages.
modern electronic instrumentation unit 5

18. Programmable Software
Involves the use of a programming language, such as:
C++, Visual C++
BASIC, Visual Basic + Add-on tools (such as VisuaLab with VTX)
Fortran C#
Advantage: flexibility
Disadvantages: complexity and steep learning curve
Programmable software involves the use of a programming language, such as C, C++, Fortran, or many other languages. The advantage of writing custom software for data acquisition is that the programmer has ultimate flexibility in what the software does. The disadvantage is that this is complex and has a steep learning curve.
modern electronic instrumentation unit 5

19. Data Acquisition Software
Does not require programming.
Enables developers to design the custom instrument best suited to their application.
Examples: TestPoint, SnapMaster, LabView, DADISP, DASYLAB, etc.
The alternative is to use data acquisition software. This does not require traditional programming. Developers can design custom instruments best suited to their application. Examples are Testpoint, SnapMaster, LabView, DADISP, DASYLAB, and others.
modern electronic instrumentation unit 5