DATA ACQUISITION SYSTEM FOR XA9846763 THE 3 MW TRIGA REACTOR AT AERE SAVAR* A.O.M. ABDUL AHAD Bangladesh Atomic Energy Commission, Atomic Energy Research Establishment, Institute of Nuclear Science and Technology, Reactor Engineering and Control Division, Dhaka, Bangladesh Abstract A 3 MW TRIGA Mark II research reactor control console has been studied in detail and the channels have been selected for monitoring, display and record using the microcomputer. Information from these channels are fed to the computer through hardware like buffer, AD converter, multiplexer, etc. for continuos display and permanent records using video monitor, printer and diskettes. Besides, the information from the console, other information like operating time, power, total burnup of fuel, operating persons, etc. are also available, With very little modifications in both hardware and software, the data logging system is now running successfully. INTRODUCTION A 3 MW TRIGA Hark II research reactor has become operational at Atomic Energy Research Establishment, Savar Dhaka since September, 1986. The reactor is being used mainly for Isotope production, neutron radiography, activation analysis and for other experiments of academic use. A triple axes spectrometer has also been installed at the reactor facility. The Control and Instrumentation group of Reactor Engineering and Control Division is engaged in R & D works in automatic control based system, and control & instrumentation of nuclear reactors. Under this project a microcomputer based system is being designed and developed to automatically monitor and record all operational parameters and relevant Information of the reactor in an efficient manner. The reactor control console has been studied in detail and the channels as per attached list (Annexure 1) have been selected for monitoring, display and record using the microcomputer. Information from these channels will be fed to the computer through hardware like buffer, AD converter, multiplexer,etc for continuous display and permanent records using video monitor, printer and diskettes. Besides, the information from the console, other information like operating time, power, total burnup of fuel, operating persons , etc. will also be available. * Research carried out in association with the IAEA under Research Contract No. BGD/6360. 11 DESCRIPTION The whole system has been shown in the block diagram (Annexure 2). Except the reactor console the remaining hardware system has been provided under this contract by the International Atomic Energy Agency and the Institute of Nuclear Science and Technology at AERE Savar. The incoming signals from the reactor console will be fed to the 8*4 channel multiplexer through a high impedance input buffer. The high input impedance will keep the reactor control system undisturbed from that of the remaining system. The multiplexer will monitor the input at regular intervals and put the information into parallel port of the computer. The personal computer contains video monitor and printer for display and instantaneous records. Diskettes will be used for permanent storage of information. As seen from the system block diagram, the hardware item include interfacing systems and personal computer with accessories. The interfacing system has been designed and fabricated using locally available components as far as practicable. The computer with accessories and some other components have been provided under this contract by the International Atomic Energy Agency. INTERFACING SYSTEM The interfacing system consists of the following : 1) high Impedance Input buffer 11) 8 units of 4- channel multiplexer i i i) A/D converter iv) parallel port the brief description of which follows : i) High Impedance Input buffer The different channels of the reactor console have been identified as shown In the Annexure-1. To isolate the reactor control system from loading and other disturbances the interfacing system 1s being provided with high Input impedance buffer unit (of the order of 10" ohms). These high input Impedance for each channel will provide quite reasonable isolation of reactor electronics for such disturbances. The circuit diagram and other details are shown in C. i i) A/D converter Most measurements of dynamic variables are provided by devices that provide information 1n forms of analog electrical signals. To interface these signals with a computer or digital 12 logic circuit, it is necessary first to perform an analog to digital conversion. Conversion must be such that a unique known relationship exists between analog and digital signals. The transfer function of an ADC is such that some analog voltage is provided as input and the conversion gives a binary number which, later on is used by computer. The bread board design and testing of A/D converter has been done in the laboratory before connecting with the reactor. AD7581 which is an 8-channel A/0 converter has been used. The details are shown In C iii) Multiplexer The computer in a data acquisition system periodically samples the values of variables and allows sample variables from many sources to be input to the computer with appropriate programming. If no control function is associated with the system the computer then outputs the information for permanent storage in hard disk/diskettes and display through video monitors and printers The basic element in multiplexing is essentially a solid state switch. It takes decoded address signal and selects the data from the selected channel by closing a switch connected to that analog input line. The actual switch elements are usually Field Effect Transistor(FET) which have an ON resistance of a few hundreds ohms and an OFF resistance of hundreds to thousands of megohms. 8 units of 4-channel multiplexer have been used in the system. IC chips 4052 have been used for the same. In general, data acquisition modules accept number of analog inputs from monitored variables called channels as either differential voltage signals(2 wire) or single ended voltage signals (referred to ground) . The computer can then select any one of the channels under programme control for input of data from that channel. Single ended configuration has been used for this system. Details have been shown in C. iv) Address decoder This part of the data acquisition system accepts an input from the computer via address lines which serve to select a particular analog channel to be sampled or other components of the Interfacing unit. The details are shown in C. v) Software The programming for the interface system between the reactor instrumentation and the PC is a time consuming work. The PC being used for this work is IBM compatible using MS DOS 4.01 Version. GW BASIC was initially chosen as the programming language. However, basic software has later been changed and 13 modified to use TURBO BASIC as the programming language. TURBO BASIC has been adopted considering its speed and efficiency. It i8 to be mentioned here that the Data Acquisition System does not propose any control function' and the programme has been developed for tho system to monitor, display and store reactor parameters and Information. The main portion of the programme have been shown in C. RESULTS OBTAINED Input buffer unit The Input buffer circuits developed for use in the Data Acquisition System (DAS) is shown below. Buffer Unit The essential feature of the operational amplifier used in this type of circuits is that very little current is drawn by the input. The input current is negligibly small indicating that the input impedance is infinite. This feature ensures that the signals input to the operational amplifier will not affect or load the input source. The input Impedance of the circuits using these components is about 10" ohms.. 14 A/D converter A/D converter AD7581 has been used as shown 1n the figure DAS:A/D Converter. The chip accepts eight analog inputs and sequentially converts each input into eight bit binary words using successive approximation technique. The conversion results are stored in an 8*8 bit dual port RAM. The device runs from a 1 MHz clock. The converter require only a -10V reference and a +5V supply. Start up logic is included on the device to establish the correct sequence. Multiplexer The CD4052 dual 4-channel multiplexer has been used in the system. These are bi-directional analog switches allowing any analog input to be used as an output and visa-versa.The switches have low "ON" resistance and low "OFF" leakage current.The devices have an enable input which when high disables all switches to their "OFF" state. The circuit diagram is shown in figure DAS-1. Decoder The details are shown in figure DAS: Decoder. The circuit diagrams of the complete system have been enclosed as DAS-1, DAS-2, DAS-3, DAS-4 and DAS-5. Software Turbo Basic has been used as the programming language. The main programme has been divided into different sections. a) Data Logging This part has been developed to record the current operational information of the reactor. The actual mode shows the parameters of the reactor when the reactor is in operation. The demonstration mode shows different channels of the reactor under simulated conditions. b) Data Review This part of the programme enables reviewing of the data already stored in the memory. The recorded data of the reactor can be retrieved and used as and when required using this mode. 15 c) Printer Routine This part of the programme enables the use of the printer for making hard copies of information already logged. d)Graphic demonstration Using this mode different system of the reactor may be displayed and explained to the visitors and trainees. Systems like horizontal and vertical sections of the reactor, core plan showing the fuel and control rod arrangement, sections of the fuel element, and control rod movement have been included. CONCLUSIONS Like any reactor, TRIGA reactor is also under strict regulatory supervision and control of the National Nuclear Safety Committee(NNSC) of BAEC.