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

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

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

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

Data Acquisition System Block Diagram modern electronic instrumentation unit 5

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

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

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

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

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

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

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

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

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

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

modern electronic instrumentation unit 5

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

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

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