PROCESNE MERITVE

Merilni sistem za merjenje procesnih veličin Kondicioniranje signala Senzor PC LabVIEW Procesna veličina(T,p,..) DAQ

Application Software (LabVIEW) Measurement Services Software Kaj je DAQ sistem? Vhodni signal Application Software (LabVIEW) V Measurement Services Software (NI-DAQmx) Conditioning Signal A/D D/A DIO TIO Izhodni signal V i A typical data acquisition system based on virtual instrumentation consists of five parts: Sensors or signals—The signals you are acquiring or generating with your data acquisition system. Signal conditioning hardware—Used to remove noise, amplify the signal, or excite sensors. This hardware is sometimes integrated with DAQ hardware. DAQ hardware—The interface between the computer and the outside world. Its primary function is to convert analog signals to digital so that the computer can interpret them. Measurement Services software—Measurement Services software forms the layer between the hardware and your application software. It should provide configuration and installation services, a programming interface, self-calibration, and other features to simplify the interface with DAQ hardware. Application-level software—This is the software program you develop using a standard programming environment such as LabVIEW, C, or Visual Basic. Step-by-Step Data Acquisition 10 ni.com

Ethernet, Serial, or Wireless DAQ Hardware opcije Ethernet, Serial, or Wireless Distributed Desktop National Instruments offers several hardware platforms for data acquisition. The most readily available platform is the desktop computer. National Instruments offers PCI data acquisition devices that plug into any desktop computer. In addition, NI provides DAQ devices for PXI/CompactPCI, which is a more rugged modular computer platform specifically for measurement and automation applications. For distributed measurements, National Instruments Compact FieldPoint platform delivers modular I/O, embedded operation, and Ethernet communication. Lastly, for portable or handheld measurements, National Instruments offers DAQ devices for USB, PCMCIA, and CompactFlash that can be used with laptops or PocketPC PDAs. PXI Portable/Handheld © National Instruments Corporation 11 Step-by-Step Data Acquisition

DAQ kartica predstavlja multifunkcijski vmesnik LabVIEW podpira NI-DAQ programe DAQ kartica ima: Analog I/O Digital I/O Counter/timer I/O Discuss components: Transducers - Convert physical measurements to electrical signals. SCXI - Signal conditioning (amplifying, linearization, etc.). DAQ Boards - Talk briefly about the boards used in the class (mention DAQ Designer to determine what boards might be needed). The LabVIEW DAQ library supports all NI DAQ boards: The same VIs are used regardless of board. Choose a DAQ board that best fits the application. LabVIEW uses NI-DAQ software: DAQ functions can be upgraded without needing to replace LabVIEW VIs. Fixes, new functions, and updates are greatly simplified.

Pri zajemanju podatkov mislimo na naslednjo klasifikacijo signalov: 1 Pri zajemanju podatkov mislimo na naslednjo klasifikacijo signalov: 1.digitalni signali -on/off signali (TTL…..) -impulzni signali (števci, merjenje časa,frekvence) 2.analogni signali -DC in počasni AC signali -časovno spremenljivi AC signali (višjefrekvenčni AC) -frekvenčno spremenljivi signali (frekvenčna analiza)

DAQ kartica ima sledeče važne parametre: -resolucija kartice (ločljivost) : (12, 16, 32, 64 bitne) -območje min. in mak. nivo vhodnega signala za pretvorbo -število kanalov -hitrost vzorčenja -tip ADC -karakteristike ojačevalnika -načini priključitve signalov (RSE, NRSE,DIFF)

Simultaneous sampling Analog Input Multiplexed Channel 0 MUX Channel 0 AMP ADC Channel 1 Channel 1 Simultaneous sampling ADC Channel 0 Channel 1 AMP The architecture of a DAQ device will affect how it samples an analog signal. National Instruments DAQ devices that perform analog input can have one of two architectures. Multiplexed—This architecture consists of one multiplexer, one instrumentation amplifier, and one Analog-to-Digital Converter (ADC). Note that all input channels share one ADC. Using only one ADC makes this architecture very cost effective, but each channel in the scan list is sampled slightly after the previous channel. M Series devices employ this architecture. Simultaneous sampling—This architecture consists of an instrumentation amplifier and an ADC for each channel. This architecture is used on the S Series devices. While this architecture is more expensive than using one ADC for all channels, it does allow for all channels to be sampled at the same time. This is important for applications like transient signal measurement and others that require exact synchronization between measurements. Step-by-Step Data Acquisition 34 ni.com

Analog Input – Sampling Rates Signal moramo vzorčiti tako, da pride do pravilne rekonstrukcuje signala Frekvenca vzorčenja : Vzorčenje mora biti 2X višje frekvence od merjenega signala. Sampling Rate is the rate at which data is sampled. The more rapidly data changes, the higher the sampling rate you must use to characterize the data accurately. Boards that have faster A/D converters can capture higher frequency signals. Aliasing is a common source of measurement error resulting from not sampling fast enough to accurately represent a signal. Assume you measure a sine wave but you choose too slow of a sampling rate. The signal appears as a lower frequency signal. This effect can either amplify or cancel other frequency components in your measurement. After you have acquired the signal, you cannot reconstruct the original signal as noise, and harmonic signals are often the source of aliased signals. An application example of this is measuring thermocouples with 50/60 Hz noise, a common problem because this noise comes from power on a standard electrical device. © National Instruments Corporation 35 Step-by-Step Data Acquisition

Analog Input – Resolution Number of bits analog-to-digital converter (ADC) uses to represent a signal Višja resolucija – merimo lahko manjše napetostne signale Time (ms) 100 200 150 50 1.25 5.00 2.50 3.75 6.25 7.50 8.75 10.00 Amplitude (Volts) 16-Bit versus 3-Bit Resolution (5 kHz Sine Wave) 16-bit 3-bit 000 001 010 011 101 110 111 | The process of digitizing an analog signal involves representing the signal with a finite set of voltage levels. The number of voltage levels available to represent the analog signal is a function of the resolution of the analog-to-digital converter(s) (ADC) in the DAQ system. Resolution specifies the number of bits, n, that the analog-to-digital converter uses to represent the analog signal. The ADC voltage range is divided into 2n divisions or levels. Each level is assigned a digital code (incrementing binary numbers), which represents a discrete voltage in the range. The ADC returns the digital code that best fits (highest possible level without going over the actual voltage) the voltage level of the analog signal. The higher the resolution, the higher the number of digital codes—hence, the higher the actual number of voltage levels that the ADC can represent. Resolution is an unchangeable parameter of a DAQ board. Step-by-Step Data Acquisition 36 ni.com

Analog Input – nastavitev ojačanja ADC Resolution: 16-bit Range: ± 10 V 10 mV signal 32 levels of resolution Range specifies the highest and lowest voltages that the board’s ADC can accept as inputs. The analog-to-digital converter found inside most data acquisition systems is generally only capable of understanding voltages. Hence, you may need to use signal conditioning to convert the information obtained from your sensors and transducers to a voltage representation. Amplification allows you to take full advantage of all of the possible measurement values associated with the resolution of the analog-to-digital converter. Consequently, it can increase the accuracy of your measurement by a factor of 100 times or more. Amplification, one of the most common types of signal conditioning, can: Increase the amplitude of your signal Provide a better match to the input range of your ADC Improve the sensitivity of your measurement Brez ojačevalnika Step-by-Step Data Acquisition 38 ni.com

Analog Input – Range and Amplification 65,536 levels of resolution AMP X100 ADC 10 mV signal Resolution: 16-bit Range: ± 10 V Z ojačevalnikom © National Instruments Corporation 39 Step-by-Step Data Acquisition

Blok diagram multifunkcijskega vmesnika

M Series – Data Acquisition lastnosti 18-bit resolution 1.25 MS/s sampling rates Več I/O 48 digital I/O Step-by-Step Data Acquisition 12 ni.com

DAQ M Series

Postavitev sistema PC in DAQ DAQ v osebnem PC

DAQ 6008

NI USB-6008 12-Bit, 10 kS/s Low-Cost Multifunction DAQ 8 analog inputs (12-bit, 10 kS/s) 2 analog outputs (12-bit, 150 S/s); 12 digital I/O; 32-bit counter Bus-powered for high mobility; built-in signal connectivity Compatible with LabVIEW, LabWindows/CVI, and Measurement Studio for Visual Studio .NET NI-DAQmx driver software and NI LabVIEW SignalExpress LE interactive data-logging software

USB 6009 http://www.ni.com/dataacquisition/compactdaq/

NI6221 http://sine.ni.com/nips/cds/view/p/lang/en/nid/14132

LabVIEW grafično razvojno okolje What is NI LabVIEW? LabVIEW is a highly productive graphical development environment with the performance and flexibility of a programming language, as well as high-level functionality and configuration utilities designed specifically for measurement and automation applications. In general-purpose programming languages, the code is as much of a concern as the application. You must pay close attention to the syntax (commas, periods, semicolons, square brackets, curly brackets, round brackets, etc.). In contrast, with LabVIEW you use icons to represent functions, and you wire them together to determine the flow of data through your program, similar to creating flowcharts. It has all the breadth and depth of a general-purpose programming language, but it is easy to use, increasing your productivity by decreasing the time required to develop your applications. You can easily divide measurement and automation application into three main parts: acquisition, analysis, and presentation of data. LabVIEW provides a seamless way to acquire your data, perform necessary analysis on that data, and present the information in a chosen format. Throughout the seminar, we touch upon each of these three components of a measurement and automation application. Each program in LabVIEW is called a virtual instrument, or VI. The VI serves as the primary building block of a LabVIEW application, and you can use it to modularize your code for efficient design, clear and concise documentation, and simplified maintenance. Each LabVIEW VI is made up of three main components: the Front Panel, Block Diagram, and the Palettes. In the coming slides, we continue our discussion of the actual development environment of LabVIEW. 4x do 10x hitrejše programiranje in merjenje Orodja za zajemanje, analizo in prikazovanje rezultatov © National Instruments Corporation 17 Step-by-Step Data Acquisition

Konec

Today’s Demo System NI-DAQmx and LabVIEW Software SCC Signal Conditioning Carrier and Modules Sensors PCMCIA DAQCard The data acquisition system used for today’s demos includes a thermocouple and strain gage connected to an SCC signal conditioning carrier. SCC provides the sensor connectivity, excitation, amplification, and filtering. The conditioned signals are output to a shielded cable and into a plug-in DAQ device. The DAQ device converts the analog signal into digital, enabling LabVIEW to acquire, analyze, and present the data. Shielded Cable © National Instruments Corporation 19 Step-by-Step Data Acquisition