Isolated 4-20 mA Current-Loop System in the Experiment of Coal Pyrolysis in H-plasma Producing Acety

Joumal of Donghua University( Eng. Ed. )Vol 26, No 5(2009) 519Isolated 4-20 mA Current-Loop System in the Experiment of CoalPyrolysis in H-plasma Producing Acetyleneshen Jie(沈洁), LUO Jia-rong(罗家融)2, CHEN Long-wei(陈龙威), MENG Yue-dong(孟月东),SHU Xing-sheng(舒兴胜), FANG Shi-dong(方世东)1 Institute of Plasma Physics, Chinese Academy of Sciences. Hefei 230031, China2 College of Science, Donghua University, Shanghai 201620, Chinaof thissystematic approach to design high performance sigrloop prevents signal distortion and instrumentation damageconditioning circuits, an to show how to implement the due to electrical noises or voltage spikes and ground loopcurrent. Galvanic isolation eliminates the problemscircuits by using isolation amplifier. The basic principle and by ground potential differences in the plant and reduces thetypical applicable circuits of the 4-20 ma current loop ones caused by electromagnetic interference. The isolatedcircuit are presented. And the experimental testing data of and safe signal subsystem ground e the signal to a cleanisolation chip T1100N, the current-limiting circuit and filter 4-20 mA current loop can separthe circuits are analyzedKey words: signal isolation; coul Pyrolysis i plasma torch1 ExperimentalCLC number: O4-39Document code: AArticle id:1672-5220(2009)05-0519-03li The basic isolated 4-20 mA systemFigure I shows the basic isolated 4-20 mA system. Anintegrated circuit is necessary to assemble complete isolatedIntroduction4-20 mA current-loop system. The isolated 4-20 mAcurrent-loop system includes two-wire transmitter, twAcetylene is one of the most important organiA current-loop isolation module T1100lchemical materials. Producing acetylene from coal protection and filter module, and low cost isolation DCpyrolysis in hydrogen-plasma torch is environmentally DC power supply module.friendly with promising applications .TechnicalThe outstanding characteristic of 4-20 mA currerparameters, including the pulverized coal flux, the loop is that they do not require any additional power supplyhydrogen flow rate and the plasma torch power, which because the modules are completely powered by the 4-20have different effects on acetylene concentration, have mA output current loop. In the system,differentbeen researched 2.3). The power-supply system has been transmitters convert the signals of flow rate, temperaturedesigned with a 4 Mw silicon controlled rectifier, whose and pressure into two-wire 4-20 mA current-loop signalsrated output voltage is 5 000 V and rated output current is The 4-20 mA current loop has become the general800 A]. This would ensure that the 2 MW plasma torchcan work stably and safely.From transmitter(Input)4·20 mA OutpDuring the experiment, the signals of process4·20mA1-5Vparameters, including the coal flux, the hydrogen and thenitrogen flow rate, the cooling water temperature of theT】100Nplasma torch, the ektexine temperature of plasma torcDIreaction chamber and the pressure at all plasma torch layersma current loop by different24vToTtransmitters. As the plasma torch operates under theV25mA/EMI 24LA-DCMV124ND2Cormvertercondition of high voltage and large current, there arehazardous high voltages and electrical noises, which maketa acquisition system unsafe and arouse errors in中国煤化工CNMHGReceived date: 2008-12-19Foundation items: Core-University Program(CUP) and Knowledge Innovation Project and Key Project of CAS (No. KJCX-L07)Correspondence should be addressed to SHEN Jie. E-mail: shenjie(a, ip520Joumal of Donghua University(Eng. Ed. )Vol 26. No 5 (2009)standard for analog signal transmission 6. because of its noise in switching power supply is composed of the PWMimmunity to noise and line resistance. Current isolation frequency ripple and switching noise. The ripple noise canmodule inputs are signals coming from transmitters, and be filtered by an LC filter. A filtering capacitor andthe outputs are always galvanically isolated 4-20 mA loop inductor should be added to the dC/DC output end. Asproportional toshown in Fihe Fl is fast-acting fuse, and the dI isThe key specifications of TIjooN are 0.1the diode to protect against voltage reverse polaritynonlinearity, 2 kHz signal bandwidth, isolation3 kva,0.22 HA/C temperature drift, and wide voltage input. 2 Results and Discussion1.2 The basic principle of isolated 4-20 mAcurrent loop sysIn the isolated system, different transducers output 4Tl100N current loop isolation chip is a kind of 20 mA current that indicates the flow rate, temperatureisolation interface that contains current signal modulation- and pressure signals. The output current of transducer anddemodulation and coupled isolation circuit. The currente isolated 4-20 mA-output current are measuredsignal on the input drives an oscillator circuit that generates respectively. From Table I(the testing data of TilooN arethe output signal through a transformer, resulting in from Highway., LTD, testing report), we can see that thegalvanic isolation between the input and the output. A isolated output current is almost consistent with the inputconverter modulates the incoming signal to a stream of Bits current and we can draw a conclusion that the isolateand protects the Bits against outside disturbances, which system has the property of high linearity and low error.allows the demodulated signal to be converted to an analogTable 1 The testing data of TI1oon atoutput signal with an extremely high degree of accuracydifferent temperatureTo satisfy the requirements of long distance transmissionwith little distortion, less input equivalent resistance25℃0℃25℃55℃75℃Input/mAenables a wide input signal voltage rangeOutput/mThe input and the output of isolated system are3.99793.99793.99954.00003.9997protected against transient voltage peak, and the supply is4.84.79724.79824.79914.79964.8001protected against reverse polarity. The transient voltage5.59755.5.59905.59995.5999suppressor(TVS)is a device used to protect vulnerable7.27.19687,19777.19897.19987.1996circuits from electrical overstress that caused by1211.995511.997011.998211.999411.9994electrostatic discharge, inductive load switching and2020.000020.003020.003020.003020.0080duced lightning u. Within the TvS, damaging voltagespikes are limited by clamping or avalanche action of siliconInput fix FLUKE525APn junction that reduces the amplitude of the transient to a Output fix KEITHLEY Model 2000 Multimeternondestructive levelThe suppressor should be as physically close to theThe plasma reaction chamber is shown in Fig 3. Thevulnerable component's ground return as possible 8 The V-shaped plasma torch is on top of the mixing chamberlower the parasitic inductance between the ground plane ofCoal powders are injected into the mixing chamber throughthe component to be protected and the TVs is, the more the flat nozzles well below the plasma plume so as not toeffective the suppressor will beintensively influence the stability of the plasma due to thedramatic local pressure increase caused by coal pyrolysis atN4001LM317+24VL木50v/0.lFD2Fig. 2 The circuit of the EM1-24LReactonAs shown in Fig. 2, the EMI-24L module includes a- Thermocoupleurrent-limited circuit and a simple LC filter to reduce theimpact of ripple noise from DC- DC power supply output中国煤化工The current-limited circuit can supply 25 mA persistentcurrent(1. 25 V,50 n=25 mA). which is used to preventCNMHGthe following circuits from creating a short circuit andH|目triggering the dc-Dc power supply overload. The rippleFig 3 Plasma reaction chamberJoumal of Donghua University(Eng. Ed. ) Vol 26. No 5(2009) 521high temperature. Reaction chamber is mainly used to current loop system in computer data acquisition systemincrease the yield of acetylene by increasing the reaction the closed loop control process. and the input and outputtime of coal powders in high-temperature hydrogen plasma circuits of the automated instruments The isolated 4-20jet. The ektexine temperature of reaction chamber is ma current loop system presented in the paper has themeasured by two w-Re thermocouples. In order to reduce property of low cost, high linearity and low error. It canhe decomposition of the acetylene to hydrogen and soot, a satisfy the needs of different customersquenching and separator system is installed at the bottom ofthe reaction chamberAcknowledgementsAs shown in Fig. 4, during the experiment, theektexine temperature of plasma torch reaction chamber hasThe authors would like to thank HUANG Chubeen measured by using the w-Re thermocouple, from Guangzhou Highway., LTD. for providing valuabletransducer and the 4-20 mA current loop isolator. The helpoltage and the current of plasma torch are 3 000 V and600 A respectively. Without the isolator, it's very difficult Referencesto measure the ektexine temperature because of highvoltage, large current and electromagnetic interference. 1 Bao Wei-ren, Li Yong-kang, Chang Li-ping. Study onThe temperature data are very important because theMain Factors Influencing Acetylene Formation during Coaltemperature of reaction chamberbe computativePyrolysis in Arc Plasma [J]. Process Safery andaccording to reaction chamber ektexine temperatureEnvironmental Protection, 2006,84(B3): 222-226Thermodynamic data show that acetylene is the only stable [2] Bitter D, Baumann H, Klein J. Relatiom between Coalhydrocarbon molecule above 1 500 C and below aboutProperites and Acetylene Yield in Plasma Pyrolsis [J]1 200 c its thermodynamic stability decreases rapidly lowel,1985,64(10);1370-1374.3] Rau E, Seglin L, Heating of Coal with Light Pulses [J].which means that the reaction temperature should becontrolled within the certain scope of the temperature [4 ]Chen Fei-yun, Zhang Ming, Fu Peng, erwhich is convenient to the acetylene productionProduction by H-Plasma Pyrolysis Coal [J]and Technology, 2006. 8(5): 591[5] Peng Jing-xiang. Applications ofs000Electronic& Computer Design World. 2000,(9): 24-26[6] Mark Stitt R, Kunst Burr David. Ic Building Blocks fromComplete Isolated 4-20 mA Current Loop Systems [EB/Cd].(2000)[2008].www.focusti.comcn/cn/lit/an/400[7] Bruce Hartwig. What Is a Silicon Transient VoltSuppressor and How Does It Work [EB/CD].(2004[2008].www.vishay.com16:06:2516:3:066:19:4616:26:27[8] Jon Schleisner, TVS Placement the Critical Path to theLeadingEdge[eb/cd].(2002)[2008].wwW.vishay.comFig. The ektexine temperature of plasma torch reaction chamber[9] Chen Long-wei, Meng Yue-dong, Shen Jie, et al. Coalsis to Acetylene Using DC3 ConclusionsEffects of System Variables on Acetylene Concentration[J]. Journal of Physics D: Applied Physics, 2009Experimental data show that the isolated 4-20current-loop system works stably and reliably in[10] Krukonis V J, Gannon R E, Modell M. Deuterium andexperiment of coal pyrolysis in H-plasma producingCarbon-13 Tagging Studies of the Plasma Pyrolysis of Coal]Dals,Tx,USA,1974:29-41acetylene. It is neceto add the isolated 4-20 mA中国煤化工CNMHG