Design Of Automatic Test And Pairing System For PT1000Based On LabVIEW

As a measure of heat consuming, heat meter has been increasinglyused in architectural buildings and other places to provide a scientific basisfor heat metering and charging. A matched pair of temperature sensorswhich is used to measure the temperature difference and installed withinthe heat meter plays a key role in the correct measurement of heat. Themajority way of detecting and matching temperature sensor in our countryis still the manualbasis, which is inefficient and error-prone. With the rapiddevelopment of electronic industrial measurement technology and dataprocessing technology, new testing methods and instruments continue toemerge. LabVIEW, developed by National Instruments as therepresentative of the new virtual instrument technology, shows thedirection of development for the next generation of automatic test systems,also provides the technical means for detection and automatic matchingprocess of emperature sensors used in heat meters.On the basis of virtual instrument technology, the designed systemuses LabVIEW graphical programming language to realize the functions ofreading, matching, processing and preserving resistance data of PT1000. Amatching algorithm is designed by the definition of "relationship value"concept to analyse the influence of one PT1000to the pairing of othercombinations, which decises the pairing order and ensures high pairingrate. In addition, the program uses a two-dimensional array to organizelarge amounts of data and facilitate the use of the Office Toolkits Toolbox,through which Excel format reports can be directly generated to save thepairing results. The program also uses the software architecture VISA andother techniques and methods that commonly used in LabVIEW to achieve communication between computer serial port and microcontroller.In terms of hardware, the system designs weak signal detection circuit,data acquisition circuit and serial communication circuit. On the basis ofthe analysis of major interference sources, a four-wire thermal resistanceconnection is used to eliminate lead resistance, and two infinite gainmultiple feedback active filters in series are designed to eliminate noisesignal above50HZ. Finally the system realizes communication betweenupper computer and lower tcomputer through RS-485mode.Practice has proved that the program interface of the system isfriendly and easy-to-use. It also features high measurement accuracy andpairing rate and achieves good results.This article is divided into six chapters:The first chapter discusses the background and significance of thisresearch project,and introduces the principle of heat meters, commonlyused detection methods of thermal resistance and the development of thevirtual instrument technology.The second chapter introduces functions required for the system andthe whole idea for hardware and software respectively.The third chapter reasearchs and introduces in detail about the basicmeasurement circuits of the temperature sensor including weak signaldetection circuit, data acquisition circuit and serial communication circuiton the basis of characteristics of PT1000platinum resistance sensor.The fourth chapter describes the system software in detail, includingthe overall structure, the realization of functional modules and programinterface. Mainly highlights the matching algorithm and processingmethods for the laege amount of data.The fifth chapter shows operation of the system in field andemphasizes the precautions when using. Measurement results are alsoanalyzed.The sixth chapter summarizes concisely about the full text and showsmain work in the whole process of design and implementation. Also proposes improvements and prospects of applications and development ofvirtual instrument technology.