基于LabVIEW的英文文獻(xiàn)

1、.1Electric Measurements with LabVIEW Dambovita Abstract: The paper presents a data acquisition system which consists in Hall effect sensors, a PCI 6023(National Instruments) data acquisition board, Lab VIEW graphical programming environment and the e*perimental results achieved by the authors concer

2、ning the behavior of ac electrical circuits. The instruments used in the measurement technique were developed as puter data base equipments, using well determined functions (the acquisition of parameters, signal processing/adapting) with the munication possibility on a serial interface or on a paral

3、lel port. Today, data acquisition boards are used and can be assembled directly into the puter, having the operation possibility of an oscilloscope. The appearance of the LabVIEW environment was motivated by the research automation activity and by the application development, based on a hierarchical

4、 instrument structure, which is posed by the users interface and the visual programming elements. Keywords：data acquisition, graphical programming, Hall effect, electric power1 Introduction The use of the LabVIEW graphical programming environment ensures the analysis and study of power measurement m

5、ethods in single-phase and three-phase alternative current circuits 3, 6, 7. The evolution in both electric measurement technique, in the electronic field and in the area of data acquisition systems, arguments the opportunity and justification of designing new instruments in order to improve the res

6、earch activity in this area 2, 3.The modern applied metrology is integrally linked with other fast-growing domains, such as puter technology, data processing and telemunications. Adaptation of the information systems techniques for the needs of measurement systems created a new interdisciplinary fie

7、ld dealing with Distributed Measurement-Control Systems (DMCS). Elements of DMCS (nodes) are distributed territorially, connected via wired or wireless network and able to e*change information between each other. Currently the research in the area of DMCS is focused on the applicability issues and a

8、dapting of new information and munication technologies for such systems 8. Nowadays, a very important issue in DMCS technology ensures the safety of munication. In many cases, the success of often costly e*periments or missions and also the biological and economical security depends on the proper fu

9、nctioning of such systems. Due to the still growing integration with telemunications and general public puter networks, the security of distributed measurement systems has been dramatically reduced. In many DMCS the information security of the network bees one of the major development problems. Info

10、rmation security issues are also very important (because of the specific openness of such systems, and ease of attack) in the wireless and mobile DMCS systems. Since the nodes of DMCS can be both socalled Measuring Servers, usually based on PCs with huge processor power, as well as mobile wireless s

11、ensors powered from battery, the e*isting disparity of calculation power makes another important issue for the development of mon methods, ensuring the safety of DMCS. Therefore there is an urgent need to develop proper methods and tools to ensure the safety and security of these systems 1, 8. The s

12、oftware plays nowadays a huge role in measurement systems and very often determines their quality. The growing processors puting power and memory capacity allows for the development of more ple* software. An important issue bees the creation of new methods and software tools for designing distribute

13、d measurement systems, and in particular low-cost and easyto- use libraries and tools for designing software that provides secure e*change of information independently of used information and munication infrastructure.E*isting software design tools dedicated for DMCS, integrated software environment

14、s such as LabVIEW, LabWindows/CVI, HPVEE, enable simple and fle*ible development process of applications, but among others do not include libraries for secure data e*change. The security problem was only slightly considered which has resulted in the introduction of certain access control mechanisms

15、to certain parts of an application (front panels and their ponents) based on login and password identification system. But there is no use of cryptographic methods, and the information between nodes is sent e*plicitly, mostly as a plain te*t.Therefore, it seems necessary to develop a plete library o

16、f functions, programs and tools tailored to specific programming environments, which would give the application or system developer the opportunity to design and simulate secure and safe distributed measurement system in an easy and intuitive way. These additives should help to ensure safe transmiss

17、ion of data in any munication infrastructure and the creation of mechanisms for authentication and integrity of both measurement and control data.In the previous work, the authors have analyzed the LabVIEW environment capabilities for efficient implementation of cryptographic algorithms 1. The ne*t

18、phase of the work, described in this paper, is to develop new mathematical tool for LabVIEW environment - a Large Number library (also known as Big Integer or arbitrary length integer library). This library allows for the putation on numbers with arbitrary (within the limits of available memory) num

19、ber of decimal digits, far e*ceeding the typical representation in puter systems (32 or 64bit). Large numbers are widely used in many popular cryptographic algorithms, including RSA, Rabin or ElGamal public-key encryption systems, used for both, data encryption and the generation of secure digital s

20、ignatures 2,3. The LN library in addition to basic arithmetic operation includes operation modulo N in the suitable rings or finite bodies, functions for calculating the opposite element in such algebras and primality test algorithms.2. Power Measurement in Single-Phase AC CircuitsThe instantaneous

21、power 1,2,3,4 to an electric dipole is defined as the product of the instantaneous values of the voltage (u) to the terminal of the dipole and the current (i) that flows through the dipole: P=ui (1) The instantaneous power can be classified into input and output power, depending on the association o

22、f the voltage (u) and the current (i), which respects the rule of receivers and generators. In a sine-wave steady-state with the T period, the active power (P) can be defined as the average value of the instantaneous power, considering a natural number of periods: For a single-phase circuit which fu

23、nctions under a sine-wave permanent rate, in which the voltage and current have the following e*pressions:it results: - the active power: P = UIcos- the reactive power: Q = UIsin (5) - the apparent power: S = UIThe ple* apparent power (S) is defined into the simplified ple* representation as the pro

24、duct between the ple* voltage (U) and the conjugate ple* current (I*):The real part of the ple* power (S) is the active power (P), the imaginary part is the reactive power (Q), the module is the apparent power (S) and the argument is equal to the phase displacement () of the circuit:For a single-pha

25、se circuit which does not function in sine-wave rate 4 and has the terminal voltage u(t):there can be defined: the active power:the reactive power:the apparent power:S=UI (11)By taking into account the relations above, we can notice that S P +Q and therefore the notion of deforming power can be intr

26、oduced:The application below (fig. 1) which is realized by using the LabVIEW graphical programming environment, basing on the presented theoretical considerations 2,5,6,7, allows the graphical display of the time variation of the voltage, the current, the instantaneous and active power. Control elem

27、ents are used in order to modify the voltage and the charge impedance parameters, and also other elements are used for indicating the voltage, the current, the power factor, the active, reactive and apparent power (in order to obtain an accurate view of the current, it is possible to multiply the am

28、plitude 1, 10, 20, 50 or 100 times).Fig.1. Single-Phase AC Circuits Operation and Power Measurement simulation2.2 Signal Conditioning The acquisition data board is a ple* system which allows parameter measurement and monitoring from a technological process, using transducers which can transform stud

29、ied physical measures into electrical voltage 1,3,4,6,7. For single-phase ac circuits, it is necessary to obtain signals with voltage-range amplitude, to be applied at the input of the board. For phase/line voltages, resistive voltage dividers (do not ensure galvanic isolation) or voltage measuremen

30、t transformers (ensure galvanic separation) can be used. Shunts (current-voltage converter) or current measurement transformers can be used for currents. The use of both voltage dividers and shunts must be done by taking into account the current through the voltage divider, the voltage drop on the s

31、hunt, the power dissipation, parasite resistances, self-heating effects, dynamic effects.Fig.2. Data acquisition systemFig.3. E*perimental resultsThe use of voltage-current measurement transformers ensures the energetic systems galvanic isolation of the measuring system, but it introduces ratio and

32、angle errors and realizes an inadequate perturbation transfer. The adopted solution was to use current and voltage transducers based on the Hall effect. The block diagram of the acquisition system is presented in fig.2 and fig.3 presents the e*perimental results.Remark: The voltage values and the pa

33、rameters of the consumers in fig. 3a, were introduced into the application realized for simulation (fig.1).3. Power Measurement in Three-Phase AC Circuits For a random receiver (Z), consisting in linear impedances, forming a system with n nodes which is alimented through a circuit with n conductors

34、1, the total ple* apparent power (S) transmitted to the receiver is:By e*pressing the potentials of the nodes using the potential differences reported to a point N having a random potential, the e*pression (3.1) bees:(14)The definitions of active and reactive power give the following results:The tot

35、al active power P (respectively the reactive power Q) consumed by a random receiver with n phases and alimented through a line of n conductors, is equal to the sum of n active single-phase powers (or reactive single-phase powers) which are given by the Ik line currents, with the UkN voltages between

36、 the n conductors and the N point. The alternative three-phase circuits have the following voltage system:If the voltage system supplies a three-phase balanced receiver, the current system will be:If the phase impedances are different, the receiver is not balanced and the absorbed currents from the

37、source can be calculated with methods that are related to star connected three-phase balanced receivers, it results:Regarding the impedance value of the neutral conductor (Z0), the voltage value will be:Fig.4. Data Acquisition System block diagramThe block diagram of the data acquisition system is p

38、resented in fig.4. The measuring methods for active/reactive power in three-phase ac circuits, depend on the type of the consumer and the number of conductors in the electric energy supply system.For three-phase circuits with neutral conductor (n=4), the generalized theorem bees:The total active pow

39、er in this case can be measured by using the 4 wattmeter method (if a random value is given to the potential of the N point) or using the 3 wattmeter method (if the potential of the N point is equal to the one of the neutral conductor).Fig.5. Data Acquisition System e*perimental results4 ConclusionThe implementation of the applications (simulating and data acquisition) into the LabVIEW graphical programming environment has been realized basing on theoretical aspects and e*perimental determinations in the