Data Acquisition Dr inż. ZDZISŁAW PÓLKOWSKI Polkowice, 2015 University of Pitesti Dolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki w Polkowicach Simedre Mirel-Adrian

Introduction Data acquisition involves gathering signals from measurement sources and digitizing the signals for storage, analysis, and presentation on a PC. Data acquisition systems come in many different PC technology forms to offer flexibility when choosing your system. You can choose from PCI, PXI, PCI Express, PXI Express, PCMCIA, USB, wireless, and Ethernet data acquisition for test, measurement, and automation applications. Consider the following five components when building a basic data acquisition system (Figure 1): Transducers and sensors Signals Signal conditioning DAQ hardware Driver and application software

What Is Data Acquisition? Data acquisition (DAQ) is the process of measuring an electrical or physical phenomenon such as voltage, current, temperature, pressure, or sound,flow rate with a computer. Data acquisition systems, as the name implies, are products and/or processes used to collect information to document or analyze some phenomenon. In the simplest form, a technician logging the temperature of an oven on a piece of paper is performing data acquisition. As technology has progressed, this type of process has been simplified and made more accurate, versatile, and reliable through electronic equipment. Equipment ranges from simple recorders to sophisticated computer systems. Data acquisition products serve as a focal point in a system, tying together a wide variety of products, such as sensors that indicate temperature, flow, level, or pressure.

Transducers Data acquisition begins with the physical phenomenon to be measured. This physical phenomenon could be the temperature of a room, the intensity of a light source, the pressure inside a chamber, the force applied to an object, or many other things. An effective data acquisition system can measure all of these different phenomena. A transducer is a device that converts a physical phenomenon into a measurable electrical signal, such as voltage or current. The ability of a data acquisition system to measure different phenomena depends on the transducers to convert the physical phenomena into signals measurable by the data acquisition hardware. Transducers are synonymous with sensors in data acquisition systems. There are specific transducers for many different applications, such as measuring temperature, pressure, or fluid flow. Table 1 shows a short list of some common phenomena and the transducers used to measure them

Signals The appropriate transducers convert physical phenomena into measurable signals. However, different signals need to be measured in different ways. For this reason, it is important to understand the different types of signals and their corresponding attributes. Signals can be categorized into two groups: Analog Signals An analog signal can exist at any value with respect to time. A few examples of analog signals include voltage, temperature, pressure, sound, and load. The three primary characteristics of an analog signal are level, shape, and frequency.

Digital Signals A digital signal cannot take on any value with respect to time. Instead, a digital signal has two possible levels: high and low. Digital signals generally conform to certain specifications that define the characteristics of the signal. They are commonly referred to as transistor-to-transistor logic (TTL). TTL specifications indicate a digital signal to be low when the level falls within 0 to 0.8 V, and the signal is high between 2 and 5 V. The useful information that you can measure from a digital signal includes the state and the rate.

Data Acquisition System Block Diagram :

Data acquisition and control hardware :

Types of Data Acquisition Three general usage types: Laboratory Distributed Portable Laboratory and distributed DAQ systems are normally put in a permanent location as these are comprised of relatively large or bulky hardware and connect to desktop PCs in some way. These systems depend upon the PC to access, process, and analyze input data and prepare it for some type of presentation. Portable DAQ systems, on the other hand, are small, lightweight units that are easily carried by hand and work with laptops or, even, no computer at all when installed at a location or site to only record data.

Laboratory and distributed data-acquisition systems typically adhere to industry-based packaging standards. For instance, some laboratory systems are mounted in standard 19-inch racks while distributed systems often use track mountings. A subset of these systems includes a host computer that accommodates data- acquisition plug-in boards. Portable systems, in contrast, have no real standardized form -- they may come in various sizes and shapes, but they are typically small and light. Further, portable systems are additionally classified as either stand-alone units or those which connect to a PC. Stand-alone units are self-contained data loggers and don't need a PC connection to function. Most modern data-acquisition systems, regardless of form factor, do their intended tasks very well; i.e., they acquire and process data. All systems have several factors in common; they need signal conditioners to convert sensor signals and other electrical inputs to a form that a processor can handle.

COMPONENTS OF DAQ The purpose of any data acquisition system is to gather useful measurement data for characterization, monitoring, or control. The specific parameters of your application will dictate the resolution, accuracy, channel count, and speed requirements for a data acquisition system. Each data acquisition system has unique functionality to serve application-specific requirements, all systems share common components that include, Signals & sensors signal conditioning DAQ hardware computer with software.